RESUMO
Objective.Motor neuroprostheses require the identification of stimulation protocols that effectively produce desired movements. Manual search for these protocols can be very time-consuming and often leads to suboptimal solutions, as several stimulation parameters must be personalized for each subject for a variety of target motor functions. Here, we present an algorithm that efficiently tunes peripheral intraneural stimulation protocols to elicit functionally relevant distal limb movements.Approach.We developed the algorithm using Bayesian optimization (BO) with multi-output Gaussian Processes (GPs) and defined objective functions based on coordinated muscle recruitment. We applied the algorithm offline to data acquired in rats for walking control and in monkeys for hand grasping control and compared different GP models for these two systems. We then performed a preliminary online test in a monkey to experimentally validate the functionality of our method.Main results.Offline, optimal intraneural stimulation protocols for various target motor functions were rapidly identified in both experimental scenarios. Using the model that performed best, the algorithm converged to stimuli that evoked functionally consistent movements with an average number of actions equal to 20% of the search space size in both the rat and monkey animal models. Online, the algorithm quickly guided the observations to stimuli that elicited functional hand gestures, although more selective motor outputs could have been achieved by refining the objective function used.Significance.These results demonstrate that BO can reliably and efficiently automate the tuning of peripheral neurostimulation protocols, establishing a translational framework to configure peripheral motor neuroprostheses in clinical applications. The proposed method can also potentially be applied to optimize motor functions using other stimulation modalities.
Assuntos
Movimento , Extremidade Superior , Algoritmos , Animais , Teorema de Bayes , Haplorrinos , RatosRESUMO
Motor cortical areas from both hemispheres play a role during functional recovery after a unilateral spinal cord injury (SCI). However, little is known about the morphologic and phenotypical differences that a SCI could trigger in corticospinal (CS) neurons of the ipsilesional and contralesional hemisphere. Using an SMI-32 antibody which specifically labeled pyramidal neurons in cortical Layers V, we investigated the impact of a unilateral cervical cord lesion on the rostral part (F6) and caudal part (F3) of the supplementary motor area (SMA) in both hemispheres of eight adult macaque monkeys compared with four intact control monkeys. We observed in F3 (but not in F6) interindividual variable and adaptive interhemispheric asymmetries of SMI-32-positive Layer V neuronal density and dendritic arborization, which are strongly correlated with the extent of the SCI as well as the duration of functional recovery, but not with the extent (percentage) of functional recovery.
Assuntos
Córtex Motor , Traumatismos da Medula Espinal , Animais , Haplorrinos , Macaca , Recuperação de Função FisiológicaRESUMO
A restricted lesion of the hand area in the primary motor cortex (M1) leads to a deficit of contralesional manual dexterity, followed by an incomplete functional recovery, accompanied by plastic changes in M1 itself and in other cortical areas on both hemispheres. Using the marker SMI-32 specific to pyramidal neurons in cortical layers III and V, we investigated the impact of a focal unilateral M1 lesion (hand representation) on the rostral part (F6) and caudal part (F3) of the supplementary motor area (SMA) in both hemispheres in nine adult macaque monkeys compared with four intact control monkeys. The M1 lesion induced a consistent interhemispheric asymmetry in density of SMI-32-positive neurons in F3 layer V (statistically significant in 8 of 9 lesioned monkeys), highly correlated with the lesion volume and with the duration of functional recovery, but not with the extent of functional recovery itself. Such interhemispheric asymmetry was neither present in the intact monkeys, as expected, nor in F6 in all monkeys. In addition, the M1 lesion also impacted on the basal dendritic arborization of F3 layer V neurons. Neuronal density was clearly less affected by the M1 lesion in F3 layer III compared with layer V. We interpret the remote effect of M1 lesion onto the density of SMI-32-positive neurons and dendritic arborization in the SMAs bilaterally as the consequence of multiple factors, such as changes of connectivity, diaschisis and various mechanisms involved in cortical plasticity underlying the functional recovery from the M1 lesion.SIGNIFICANCE STATEMENT The motor system of macaque monkeys, in addition to be similarly organized as in humans, is a good candidate to study the impact of a focal lesion of the main contributor to voluntary movements, the primary motor cortex (M1), on non-primary motor cortical areas also involved in manual dexterity, both at behavioral and structural levels. Our results show that a unilateral permanent lesion of M1 hand area in nine monkeys affects the interhemispheric balance of the number of SMI-32-positive pyramidal neurons in the cortical layer V of the supplementary motor area, in a way strongly correlated to the lesion volume and duration of the incomplete functional recovery.
Assuntos
Lateralidade Funcional/fisiologia , Córtex Motor/patologia , Córtex Motor/fisiologia , Destreza Motora/fisiologia , Desempenho Psicomotor/fisiologia , Fatores Etários , Animais , Craniotomia/métodos , Macaca fascicularis , Macaca mulatta , Córtex Motor/citologiaRESUMO
Cortico-cortical connectivity has become a major focus of neuroscience in the last decade but most of the connectivity studies focused on intrahemispheric circuits. Little has been reported about information acquired and processed in the premotor cortex and its functional connection with its homotopic counterpart in the opposite hemisphere via the corpus callosum. In non-human primates (macaques) lateralization is not well documented and its exact role is still unknown. The present study confirms in two macaques the existence of homotopic contralateral projections and completes the picture by further exploring heterotopic (non-motor) callosal projections. This was tested by injecting retrograde tracers in the premotor cortical areas PMv and PMd (targets). Our method consisted of identifying the connections with all the homo- and heterotopic cortical areas located in the contralateral hemisphere. The results showed that PMd and PMv receive multiple low-density labeled inputs from the opposite heterotopic prefrontal, parietal, motor, insular and temporal regions. Such unexpected collection of transcallosal inputs from heterotopic areas suggests that the premotor areas communicate with other modalities through long distance low-density networks which could have important implications in the understanding of sensorimotor and multimodal integration.
Assuntos
Corpo Caloso/citologia , Córtex Motor/citologia , Animais , Lateralidade Funcional , Macaca fascicularis , Macaca mulatta , Vias Neurais/citologia , Técnicas de Rastreamento Neuroanatômico , Neurônios/citologia , FotomicrografiaRESUMO
In the context of an autologous adult neural cell ecosystem (ANCE) transplantation study, four intact adult female macaque monkeys underwent a unilateral biopsy of the dorsolateral prefrontal cortex (dlPFC) to provide the cellular material needed to obtain the ANCE. Monkeys were previously trained to perform quantitative motor (manual dexterity) tasks, namely, the "modified-Brinkman board" task and the "reach and grasp drawer" task. The aim of the present study was to extend preliminary data on the role of the prefrontal cortex in motor habit and test the hypothesis that dlPFC contributes to predict the grip force required when a precise level of force to be generated is known beforehand. As expected for a small dlPFC biopsy, neither the motor performance (score) nor the spatiotemporal motor sequences were affected in the "modified-Brinkman board" task, whereas significant changes (mainly decreases) in the maximal grip force (force applied on the drawer knob) were observed in the "reach and grasp drawer" task. The present data in the macaque monkey related to the prediction of grip force are well in line with the previous fMRI data reported for human subjects. Moreover, the ANCE transplantation strategy (in the case of stroke or Parkinson's disease) based on biopsy in dlPFC does not generate unwanted motor consequences, at least as far as motor habit and motor performance are concerned in the context of a sequential grasping a small objects, which does not require the development of significant force levels.
Assuntos
Habituação Psicofisiológica/fisiologia , Força da Mão/fisiologia , Atividade Motora/fisiologia , Córtex Pré-Frontal/fisiologia , Desempenho Psicomotor/fisiologia , Animais , Feminino , Lateralidade Funcional , Processamento de Imagem Assistida por Computador , Macaca fascicularis , Imageamento por Ressonância Magnética , Córtex Pré-Frontal/diagnóstico por imagem , Amplitude de Movimento Articular/fisiologiaRESUMO
The present study was aimed at developing a new strategy to design and anchor custom-fitted implants, consisting of a head fixation device and a chronic recording chamber, on the skull of adult macaque monkeys. This was done without the use of dental resin or orthopedic cement, as these modes of fixation exert a detrimental effect on the bone. The implants were made of titanium or tekapeek and anchored to the skull with titanium screws. Two adult macaque monkeys were initially implanted with the head fixation device several months previous to electrophysiological investigation, to allow optimal osseous-integration, including growth of the bone above the implant's footplate. In a second step, the chronic recording chamber was implanted above the brain region of interest. The present study proposes two original approaches for both implants. First, based on a CT scan of the monkey, a plastic replicate of the skull was obtained in the form of a 3D print, used to accurately shape and position the two implants. This would ensure a perfect match with the skull surface. Second, the part of the implants in contact with the bone was coated with hydroxyapatite, presenting chemical similarity to natural bone, thus promoting excellent osseous-integration. The longevity of the implants used here was 4 years for the head fixation device and 1.5 years for the chronic chamber. There were no adverse events and daily care was easy. This is clear evidence that the present implanting strategy was successful and provokes less discomfort to the animals.
Assuntos
Eletrofisiologia/instrumentação , Eletrofisiologia/métodos , Neurociências/instrumentação , Neurociências/métodos , Próteses e Implantes , Animais , Hidroxiapatitas , Macaca , Crânio , TitânioRESUMO
In adult macaque monkeys subjected to an incomplete spinal cord injury (SCI), corticospinal (CS) fibers are rarely observed to grow in the lesion territory. This situation is little affected by the application of an anti-Nogo-A antibody which otherwise fosters the growth of CS fibers rostrally and caudally to the lesion. However, when using the Sternberger monoclonal-incorporated antibody 32 (SMI-32), a marker detecting a non-phosphorylated neurofilament epitope, numerous SMI-32-positive (+) fibers were observed in the spinal lesion territory of 18 adult macaque monkeys; eight of these animals had received a control antibody infusion intrathecally for 1 month after the injury, five animals an anti-Nogo-A antibody, and five animals received an anti-Nogo-A antibody together with brain-derived neurotrophic factor (BDNF). These fibers occupied the whole dorso-ventral axis of the lesion site with a tendency to accumulate on the ventral side, and their trajectories were erratic. Most of these fibers (about 87%) were larger than 1.3 µm and densely SMI-32 (+) stained. In the undamaged spinal tissue, motoneurons form the only large population of SMI-32 (+) neurons which are densely stained and have large diameter axons. These data therefore suggest that a sizeable proportion of the fibers seen in the lesion territory originate from motoneurons, although fibers of other origins could also contribute. Neither the presence of the antibody neutralizing Nogo-A alone, nor the presence of the antibody neutralizing Nogo-A combined with BDNF influenced the number or the length of the SMI-32 (+) fibers in the spinal lesion area. In summary, our data show that after a spinal cord lesion in adult monkeys, the lesion site is colonized by fibers, a large portion of which presumably originate from motoneurons.
Assuntos
Proteínas da Mielina/imunologia , Fibras Nervosas/fisiologia , Regeneração Nervosa/fisiologia , Recuperação de Função Fisiológica/fisiologia , Traumatismos da Medula Espinal/patologia , Animais , Anticorpos/uso terapêutico , Fator Neurotrófico Derivado do Encéfalo/uso terapêutico , Proteoglicanas de Sulfatos de Condroitina/metabolismo , Modelos Animais de Doenças , Feminino , Injeções Espinhais , Macaca , Masculino , Proteínas da Mielina/metabolismo , Fibras Nervosas/efeitos dos fármacos , Regeneração Nervosa/efeitos dos fármacos , Proteínas de Neurofilamentos/metabolismo , Proteínas Nogo , Recuperação de Função Fisiológica/efeitos dos fármacos , Traumatismos da Medula Espinal/tratamento farmacológico , Traumatismos da Medula Espinal/fisiopatologiaRESUMO
The insula of Reil represents a large cortical territory buried in the depth of the lateral sulcus and subdivided into 3 major cytoarchitectonic domains: agranular, dysgranular, and granular. The present study aimed at reinvestigating the architectonic organization of the monkey's insula using multiple immunohistochemical stainings (parvalbumin, PV; nonphosphorylated neurofilament protein, with SMI-32; acetylcholinesterase, AChE) in addition to Nissl and myelin. According to changes in density and laminar distributions of the neurochemical markers, several zones were defined and related to 8 cytoarchitectonic subdivisions (Ia1-Ia2/Id1-Id3/Ig1-Ig2/G). Comparison of the different patterns of staining on unfolded maps of the insula revealed: 1) parallel ventral to dorsal gradients of increasing myelin, PV- and AChE-containing fibers in middle layers, and of SMI-32 pyramidal neurons in supragranular layers, with merging of dorsal and ventral high-density bands in posterior insula, 2) definition of an insula "proper" restricted to two-thirds of the "morphological" insula (as bounded by the limiting sulcus) and characterized most notably by lower PV, and 3) the insula proper is bordered along its dorsal, posterodorsal, and posteroventral margin by a strip of cortex extending beyond the limits of the morphological insula and continuous architectonically with frontoparietal and temporal opercular areas related to gustatory, somatosensory, and auditory modalities.
Assuntos
Mapeamento Encefálico , Córtex Cerebral/anatomia & histologia , Córtex Cerebral/metabolismo , Acetilcolinesterase/metabolismo , Animais , Macaca fascicularis , Macaca mulatta , Bainha de Mielina/metabolismo , Fibras Nervosas/metabolismo , Fibras Nervosas/fisiologia , Vias Neurais/fisiologia , Proteínas de Neurofilamentos/metabolismo , Neurônios/citologia , Neurônios/metabolismo , Parvalbuminas/metabolismoRESUMO
In order to interact with the multisensory world that surrounds us, we must integrate various sources of sensory information (vision, hearing, touch...). A fundamental question is thus how the brain integrates the separate elements of an object defined by several sensory components to form a unified percept. The superior colliculus was the main model for studying multisensory integration. At the cortical level, until recently, multisensory integration appeared to be a characteristic attributed to high-level association regions. First, we describe recently observed direct cortico-cortical connections between different sensory cortical areas in the non-human primate and discuss the potential role of these connections. Then, we show that the projections between different sensory and motor cortical areas and the thalamus enabled us to highlight the existence of thalamic nuclei that, by their connections, may represent an alternative pathway for information transfer between different sensory and/or motor cortical areas. The thalamus is in position to allow a faster transfer and even an integration of information across modalities. Finally, we discuss the role of these non-specific connections regarding behavioral evidence in the monkey and recent electrophysiological evidence in the primary cortical sensory areas.
Assuntos
Vias Aferentes/anatomia & histologia , Córtex Auditivo/anatomia & histologia , Vias Neurais/anatomia & histologia , Vias Aferentes/fisiologia , Animais , Córtex Auditivo/fisiologia , Comportamento , Comportamento Animal , Mapeamento Encefálico/métodos , Córtex Cerebral/anatomia & histologia , Eletrofisiologia/métodos , Haplorrinos , Humanos , Modelos Biológicos , Modelos Neurológicos , Córtex Motor/fisiologia , Vias Neurais/fisiologia , Tálamo/fisiologiaRESUMO
The present study describes in primates the effects of a spinal cord injury on the number and size of the neurons in the magnocellular part of the red nucleus (RNm), the origin of the rubrospinal tract, and evaluates whether a neutralization of Nogo-A reduces the lesioned-induced degenerative processes observed in RNm. Two groups of monkeys were subjected to unilateral section of the spinal cord affecting the rubrospinal tract; one group was subsequently treated with an antibody neutralizing Nogo-A; the second group received a control antibody. Intact animals were also included in the study. Counting neurons stained with a monoclonal antibody recognizing non-phosphorylated epitopes on neurofilaments (SMI-32) indicated that their number in the contralesional RNm was consistently inferior to that in the ipsilesional RNm, in a proportion amounting up to 35%. The lesion also induced shrinkage of the soma of the neurons detected in the contralesional RNm. Infusing an anti-Nogo-A antibody at the site of the lesion did not increase the proportion of SMI-32 positive rubrospinal neurons in the contralesional RNm nor prevent shrinkage.
Assuntos
Anticorpos Monoclonais/farmacologia , Proteínas da Mielina/antagonistas & inibidores , Neurônios/patologia , Tratos Piramidais/patologia , Núcleo Rubro/patologia , Traumatismos da Medula Espinal/patologia , Animais , Axotomia , Vértebras Cervicais , Lateralidade Funcional/fisiologia , Humanos , Macaca , Proteínas de Neurofilamentos/efeitos dos fármacos , Proteínas NogoRESUMO
The present study aimed at investigating the time span it takes to remove a static mechanical allodynia (SMA) in humans suffering from chronic peripheral neuropathic pain. Forty-three subjects were included in the study and, during somatosensory rehabilitation, their SMA territory was precisely mapped. They then underwent distant vibrotactile counter stimulation (DVCS) treatment. It was observed that, with DVCS, SMA disappeared in all cases, and was transformed into an underlying hypoaesthesia. It was found that the "tenderness to touch" symptom (which is SMA) was located in the same territory as the underlying hypoaesthesia, which was located on a part of the cutaneous territory of a partially damaged nerve. These results demonstrate that treating patients suffering from neuropathic pain with DVCS revealed a skin territory of denervation that was previously masked by SMA. Thus, SMA can be considered as a paradoxical painful hypoaesthesia. Furthermore, mapping SMA is a valuable source of information for our understanding of abnormal sensory processing in neuropathic pain patients. We conclude that the mapping of the zone of hypersensitivity on the skin in humans suffering from chronic peripheral neuropathic pain improves diagnosis. The mapping of the zone of hypersensitivity is a tool to presume which branch of the peripheral nerve is damaged. The location of the axonal lesions is at the periphery, while the mechanism of pain sensitization is probably central and referred peripherally to the skin by a painful hypoaesthesia.
Assuntos
Hiperestesia/fisiopatologia , Hiperestesia/reabilitação , Hipestesia/fisiopatologia , Mecanorreceptores/fisiopatologia , Neuralgia/reabilitação , Limiar da Dor/fisiologia , Doenças do Sistema Nervoso Periférico/reabilitação , Pele/inervação , Vibração/uso terapêutico , Doença Crônica , Seguimentos , Humanos , Medição da Dor/métodos , Resultado do TratamentoRESUMO
The corticothalamic projection includes a main, modulatory projection from cortical layer VI terminating with small endings whereas a less numerous, driving projection from layer V forms giant endings. Such dual pattern of corticothalamic projections is well established in rodents and cats for many cortical areas. In non-human primates (monkeys), it has been reported for the primary sensory cortices (A1, V1, S1), the motor and premotor cortical areas and, in the parietal lobe, also for area 7. The present study aimed first at refining the cytoarchitecture parcellation of area 5 into the sub-areas PE and PEa and, second, establishing whether area 5 also exhibits this dual pattern of corticothalamic projection and what is its precise topography. To this aim, the tracer biotinylated dextran amine (BDA) was injected in area PE in one monkey and in area PEa in a second monkey. Area PE sends a major projection terminating with small endings to the thalamic lateral posterior nucleus (LP), ventral posterior lateral nucleus (VPL), medial pulvinar (PuM) and, but fewer, to ventral lateral posterior nucleus, dorsal division (VLpd), central lateral nucleus (CL) and center median nucleus (CM), whereas giant endings formed restricted terminal fields in LP, VPL and PuM. For area PEa, the corticothalamic projection formed by small endings was found mainly in LP, VPL, anterior pulvinar (PuA), lateral pulvinar (PuL), PuM and, to a lesser extent, in ventral posterior inferior nucleus (VPI), CL, mediodorsal nucleus (MD) and CM. Giant endings originating from area PEa formed restricted terminal fields in LP, VPL, PuA, PuM, MD and PuL. Furthermore, the origin of the thalamocortical projections to areas PE and PEa was established, exhibiting clusters of neurons in the same thalamic nuclei as above, in other words predominantly in the caudal thalamus. Via the giant endings CT projection, areas PE and PEa may send feedforward, transthalamic projections to remote cortical areas in the parietal, temporal and frontal lobes contributing to polysensory and sensorimotor integration, relevant for visual guidance of reaching movements for instance.
Assuntos
Córtex Cerebral/fisiologia , Lobo Parietal/fisiologia , Tálamo/fisiologia , Animais , Autorradiografia , Biotina/análogos & derivados , Interpretação Estatística de Dados , Dextranos , Corantes Fluorescentes , Imuno-Histoquímica , Macaca fascicularis , Macaca mulatta , Sondas Moleculares , Terminações Nervosas/fisiologia , Vias Neurais/fisiologia , Conjugado Aglutinina do Germe de Trigo-Peroxidase do Rábano SilvestreRESUMO
The present study was designed to complete two previous reports [Loquet, G., Rouiller, E.M., 2002. Neural adaptation to pulsatile acoustical stimulation in the cochlear nucleus of the rat. Hear. Res. 171, 72-81; Loquet, G., Meyer, K., Rouiller, E.M., 2003. Effects of intensity of repetitive acoustic stimuli on neural adaptation in the ventral cochlear nucleus of the rat. Exp. Brain Res. 153, 436-442] on neural adaptation properties in the auditory system of the rat. Again, auditory near-field evoked potentials (ANEPs) were recorded in response to 250-ms trains of clicks from an electrode chronically implanted in the ventral cochlear nucleus (VCN). Up to now, our interest had focused on the adaptive behavior of the first one (N1) of the two negative ANEP components. A re-examination of our data for the second negative component (N2) was now undertaken. Results show that the adaptation time course observed for N2 displayed the same three-stage pattern previously reported for N1. Similarly, adaptation became more pronounced and occurred faster as stimulus intensity and/or repetition rate were increased. Based on latency data which suggest N1 and N2 to be mainly due to the activity of auditory-nerve (AN) fibers and cochlear nucleus neurons, respectively, it was concluded that neural adaptation assessed by gross-potentials was similar in the AN and VCN. This finding is meaningful in the context of our search to restore normal adaptation phenomena via electro-auditory hearing with an auditory brainstem implant on the same lines as our work in cochlear implants.
Assuntos
Estimulação Acústica/métodos , Nervo Coclear/fisiologia , Núcleo Coclear/fisiologia , Plasticidade Neuronal , Adaptação Fisiológica , Animais , Potenciais Evocados Auditivos do Tronco Encefálico , Masculino , Vias Neurais/fisiologia , Ratos , Ratos Long-Evans , Tempo de Reação , Período Refratário EletrofisiológicoRESUMO
The effects of a unilateral interruption of the dorsolateral funiculus at cervical level on the survival of neurons in the motor cortex were investigated in macaque monkeys. The lesion was made on the left side at the transition region between the 7(th) and 8(th) cervical segments, above the motoneurons controlling hand muscles. As a result, the homolateral hand became paretic, although an incomplete recovery of manual dexterity took place during 2 months post-lesion. A quantitative anatomical assessment of pyramidal neurons in layer V was performed in the hindlimb area of the primary motor cortex and in the supplementary motor area (SMA proper). The pyramidal neurons were visualized using the marker SMI-32 and thus included the subpopulation of corticospinal neurons. These quantitative data demonstrated that the vast majority of the axotomized corticospinal (CS) neurons did not degenerate. Rather, their somata shrank, compared to the opposite hemisphere or to intact monkeys. This conclusion is in contrast to some previous studies in monkeys that argued for a substantial degeneration of motor cortex neurons as a result of transection of the corticospinal tract; yet in agreement with others that concluded the survival of most CS neurons. The survival of the majority of CS axotomized neurons is also consistent with the observation of numerous CS axons 1 mm above the cervical hemisection.
Assuntos
Córtex Motor/fisiopatologia , Tratos Piramidais/lesões , Tratos Piramidais/fisiopatologia , Degeneração Retrógrada/fisiopatologia , Traumatismos da Medula Espinal/fisiopatologia , Medula Espinal/fisiopatologia , Animais , Anticorpos , Axônios/patologia , Axônios/fisiologia , Axônios/ultraestrutura , Axotomia , Biomarcadores/metabolismo , Contagem de Células , Morte Celular/fisiologia , Tamanho Celular , Sobrevivência Celular/fisiologia , Vértebras Cervicais , Lateralidade Funcional/fisiologia , Mãos/inervação , Mãos/fisiopatologia , Macaca mulatta , Córtex Motor/patologia , Neurônios Motores/patologia , Paresia/etiologia , Paresia/patologia , Paresia/fisiopatologia , Células Piramidais/patologia , Tratos Piramidais/patologia , Recuperação de Função Fisiológica/fisiologia , Degeneração Retrógrada/etiologia , Degeneração Retrógrada/patologia , Medula Espinal/patologia , Traumatismos da Medula Espinal/patologia , Fatores de TempoRESUMO
To study neural adaptation as a function of stimulus intensity, auditory near-field evoked potentials were recorded from the ventral cochlear nucleus in awake Long Evans rats. Responses to 250-ms trains of repetitive clicks (pulse rates ranging from 100 to 1000 pulses per second) were collected at stimulus intensities of 5, 10, 30, 50 and 70 dB SPL. The amplitude of the first negative (N1) component of the average evoked potentials to individual pulses in the train was measured by using a subtraction method. The N1 responses were normalized with respect to the highest cochlear nucleus potential observed in the train, and then plotted as a function of click position in the train. As expected, the general trend of the curves was an exponential decay reaching a plateau more or less rapidly as a function of both intensity and rate of stimulation. Fitting these curves with exponential decay equations revealed that the rapid time constant decreased for increasing stimulus intensities whereas the short-term time constant is relatively independent of intensity. The amount of adaptation (expressed as the ratio of the plateau to the first peak amplitude) was substantially less prominent at low intensities (5-10 dB SPL) and low rates (100-200 pulses per second) than at higher intensities and high rates. These results indicate that adaptation patterns obtained in the ventral cochlear nucleus by using near-field evoked potentials exhibit properties comparable to those already present at the level of the auditory nerve.
Assuntos
Adaptação Psicológica/fisiologia , Vias Auditivas/fisiologia , Percepção Auditiva/fisiologia , Núcleo Coclear/fisiologia , Potenciais Evocados Auditivos/fisiologia , Estimulação Acústica , Animais , Nervo Coclear/fisiologia , Masculino , Periodicidade , Ratos , Ratos Long-Evans , Tempo de Reação/fisiologiaRESUMO
Previous anatomical experiments have demonstrated the existence of a direct, bilateral projection from the auditory cortex (AC) to the cochlear nucleus (CN). However, the precise relationship between the origin of the projection in the AC and the distribution of axon terminals in the CN is not known. Moreover, the influence of this projection on CN principal cells has not been studied before. The aim of the present study was two-fold. First, to extend the anatomical data by tracing anterogradely the distribution of cortical axons in the CN by means of restricted injections of biotinylated dextran amine (BDA) in physiologically characterized sites in the AC. Second, in an in vitro isolated whole brain preparation (IWB), to assess the effect of electrical stimulation of the AC on CN principal cells from which intracellular recordings were derived. BDA injections in the tonotopically organized primary auditory cortex and dorsocaudal auditory field at high and low best frequency (BF) sites resulted in a consistent axonal labeling in the ipsilateral CN of all injected animals. In addition, fewer labeled terminals were observed in the contralateral CN, but only in the animals subjected to injections in low BF region. The axon terminal fields consisting of boutons en passant or terminaux were found in the superficial granule cell layer and, to a smaller extent, in the three CN subdivisions. No axonal labeling was seen in the CN as result of BDA injection in the secondary auditory area (dorsocaudal belt). In the IWB, the effects of ipsilateral AC stimulation were tested in a population of 52 intracellulary recorded and stained CN principal neurons, distributed in the three CN subdivisions. Stimulation of the AC evoked slow late excitatory postsynaptic potentials (EPSPs) in only two cells located in the dorsal CN. The EPSPs were induced in a giant and a pyramidal cell at latencies of 20 ms and 33 ms, respectively, suggesting involvement of polysynaptic circuits. These findings are consistent with anatomical data showing sparse projections from the AC to the CN and indicate a limited modulatory action of the AC on CN principal cells.
Assuntos
Córtex Auditivo/citologia , Vias Auditivas/citologia , Percepção Auditiva/fisiologia , Biotina/análogos & derivados , Núcleo Coclear/citologia , Terminações Pré-Sinápticas/ultraestrutura , Animais , Córtex Auditivo/fisiologia , Vias Auditivas/fisiologia , Tamanho Celular/fisiologia , Núcleo Coclear/fisiologia , Dendritos/fisiologia , Dendritos/ultraestrutura , Dextranos , Estimulação Elétrica , Potenciais Pós-Sinápticos Excitadores/fisiologia , Feminino , Lateralidade Funcional/fisiologia , Cobaias , Masculino , Terminações Pré-Sinápticas/fisiologia , Tempo de Reação/fisiologia , Transmissão Sináptica/fisiologiaRESUMO
In the past decade, there have been considerable advances in understanding the neuronal bases of sensory and motor map reorganisation in adults and it is now clear that cortical representations are not invariant and stable, but rather, are dynamic and can continuously be modified. In human subjects, substantial advances in this field have been possible because of the spectacular development of non-invasive imaging and brain stimulation techniques. This review addresses specific questions about the capacity of motor maps in adult primates, including man, to change in response to behaviourally relevant experiences or as a result of central or peripheral lesion. The first part of this review deals with recent progress in understanding the role of the primary motor cortex (M1) in both motor control and cognition. The organisation and function of multiple "non-primary" motor areas located rostrally to the primary motor cortex and in the cingulate cortex are also discussed. This review then focuses on advances made in understanding motor cortex plasticity in different conditions. Firstly, since representations in M1 have been shown to change after motor learning, the contribution of M1 in motor learning has been insinuated; arguments against and in favour of this view are discussed. In addition, data suggesting that intracortical circuitry of M1 may play a role in map reorganisation following motor learning are also evaluated. Secondly, a large body of evidence from both animal and human observations is reviewed that confirms that M1 representations can also be altered as a result of changes in availability of effectors or following sensory deprivation. The mechanisms underlying such a plasticity of cortical maps following peripheral lesions are increasingly well understood. Thirdly, we discuss data showing that a corticospinal system lesion can lead to a complete reorganisation of the area allocated to the hand representation in the primary motor cortex or to a reorganization of the whole network of motor areas responsible for voluntary movements. As a conclusion, therapeutical perspectives that result from a better understanding of those various mechanisms responsible for motor map plasticity are briefly discussed.
Assuntos
Antipsicóticos/uso terapêutico , Encefalopatias/terapia , Mapeamento Encefálico , Fenômenos Eletromagnéticos/métodos , Córtex Motor/anatomia & histologia , Córtex Motor/fisiologia , Plasticidade Neuronal/fisiologia , Animais , Encéfalo/fisiologia , Encefalopatias/fisiopatologia , Encefalopatias/psicologia , Cognição/fisiologia , Estimulação Elétrica , Eletroencefalografia , Humanos , Primatas , Terminologia como AssuntoRESUMO
To assess whether striatal and pallidal neurones may contribute to bimanual co-ordination, two macaque monkeys were trained to perform a delayed conditional sequence of co-ordinated pull and grasp movements, executed either bimanually or unimanually. Most of the 58 task-related neurones, recorded from the caudate nucleus, putamen, external and internal divisions of the globus pallidus, exhibited an activity related to the execution of the movements. Only a quarter of neurones displayed preparatory activity. The majority of units exhibited a significant modulation of activity in unimanual trials irrespective of the hand used to perform the task. In bimanual trials, one-third of units exhibited discharge patterns reflecting a bimanual synergy, suggesting a possible role for basal ganglia in inter-limb co-operation.
Assuntos
Corpo Estriado/fisiologia , Globo Pálido/fisiologia , Mãos/fisiologia , Macaca mulatta/fisiologia , Atividade Motora/fisiologia , Neurônios/fisiologia , Animais , Lateralidade Funcional , Distribuição AleatóriaRESUMO
Single neuronal activity was recorded from the dorsal premotor cortex (PMd), the cingulate motor area (CMA) and the posterior parietal cortex (PPC) in two Macaca fascicularis trained to perform a delayed conditional sequence of coordinated pull and grasp movements. The monkey had to perform three types of trials instructed in a random manner: (i) bimanually, using the two hands in a coordinated sequence of movements; (ii) unimanually, using the left hand only; (iii) unimanually, using the right hand only. The aim of this study was first to assess the bilateral relationships of the three cortical areas for unimanual motor control. Second, to establish whether the three cortical areas contain units reflecting bimanual synergy. A total of 255 task-related neurons were recorded from the PMd, CMA and PPC, where most neurons exhibited a significant modulation of activity in both contralateral and ipsilateral unimanual trials (bilateral neurons: 85, 77 and 61%, respectively). Lower proportions of neurons in PMd (7%), CMA (16%) and PPC (6%) were active in unimanual contralateral trials, but not in unimanual ipsilateral trials. The reverse (modulation of activity in ipsilateral but not contralateral unimanual trials) represented 5% of neurons in PMd, 7% in CMA and 3% in PPC. When comparing unimanual and bimanual trials to search evidence for bimanual coordination, 57% of PMd task-related neurons were classified as bimanual, defined as units in which the activity observed in bimanual trials could not be predicted from that associated with unimanual trials when comparing the same events related to the same arm. The proportion of bimanual neurons in CMA (56%) was comparable to that found in PMd (55%), whereas PPC exhibited a higher proportion of bimanual neurons (74%). Furthermore, comparison of the present data with our previous results regarding the supplementary (SMA) and primary (M1) motor cortical areas shows that there is no statistically significant difference between PMd, CMA, SMA and M1 with respect to the proportions of bimanual neurons. Altogether, these results suggest that the five cortical areas PMd, CMA, PPC, SMA and M1 are participating to the control of sequential bimanually coordinated movements. Inter-limb coordination may thus be controlled by a widely distributed network including several cortical and sub-cortical areas.
Assuntos
Giro do Cíngulo/fisiologia , Córtex Motor/fisiologia , Movimento/fisiologia , Lobo Parietal/fisiologia , Animais , Eletrofisiologia , Lateralidade Funcional/fisiologia , Giro do Cíngulo/citologia , Mãos/inervação , Mãos/fisiologia , Macaca fascicularis , Córtex Motor/citologia , Neurônios Motores/fisiologia , Lobo Parietal/citologia , Desempenho Psicomotor/fisiologia , Movimentos Sacádicos/fisiologiaRESUMO
Recent anatomical tracing methods have revealed new principles underlying the organization of corticothalamic connections in the mammalian nervous system. These data demonstrated the distribution of two types of synaptic contacts in the corticothalamic projection: small (<1 microm) and giant (2-10 microm) axon terminals. We compare the organization of corticothalamic projections in the auditory, somatosensory, visual, and motor systems of a variety of mammalian species, including the monkey. In all these systems and species, both types of corticothalamic terminals have been observed. Small endings formed the major corticothalamic terminal field, whereas giant terminals were less numerous and formed additional terminal fields together with small terminals. After comparing their spatial distribution, as well as the degree of reciprocity between the corticothalamic and thalamocortical projections, different roles are proposed for small and giant endings. Small terminals are typically present in the projection serving the feed-back control of the cerebral cortex on the thalamic nucleus from which it receives its main projection. In contrast, giant terminals are involved in feed-forward projections by which activity from a cortical area is distributed, via the thalamus, to other parts of the cerebral cortex. The cross-species and cross-systems comparison reveals differences in the mode of feed-forward projection, which may be involved in the activation of other parts of the same cortical area or form part of a projection that activates other cortical areas.