Cue familiarity is represented in monkey medial prefrontal cortex during visuomotor association learning.

To examine functional roles of the medial prefrontal cortex (mPFC) in visuomotor association learning, neuronal activity in the mPFC of a behaving monkey was recorded during this learning. The monkey was presented a cueing visual stimulus, and required to push, pull or turn a manipulator according to the cue following a delay period. Under the control condition, three cues (circle, triangle and square) instructed the monkey to the three responses in a block of trials. After 2 months of training the animal was familiar with these cue-response associations. Under the learning condition, two of the three familiar cues and one novel cue were presented in a block. The monkey initially did not know what the novel cue instructed at first and learned a new cue-response association by trial and error. Neurons in the mPFC showed marked responses to cue presentation, and cue responses changed depending on whether cues were familiar or novel. A group of mPFC neurons responded to novel cues, but not to familiar cues. Another group of neurons responded to familiar cues, but not to novel cues. In a subgroup of these familiar cue-selective neurons, cue response was increased under the learning condition compared to the control condition. These results suggest that mPFC neurons differentiate between familiar and novel instructions, and that the neurons responsive to familiar stimuli enhance their modulations when both familiar and novel instructions have to be processed during task performance.

Organization of prefrontal outflow toward frontal motor-related areas in macaque monkeys.

Linkage between the prefrontal cortex and the primary motor cortex is mediated by nonprimary motor-related areas of the frontal lobe. In an attempt to analyse the organization of the prefrontal outflow from area 46 toward the frontal motor-related areas, we investigated the pattern of projections involving the higher-order motor-related areas, such as the presupplementary motor area (pre-SMA) and the rostral cingulate motor area (CMAr). Tracer injections were made into these motor-related areas (their forelimb representation) on the medial wall that had been identified electrophysiologically. The following data were obtained from a series of tract-tracing experiments in Japanese monkeys. (i) Only a few neurons in area 46 were retrogradely labelled from the pre-SMA and CMAr; (ii) terminal labelling from area 46 occurred sparsely in the pre-SMA and CMAr; (iii) a dual labelling technique revealed that the sites of overlap of anterograde labelling from area 46 and retrograde labelling from the pre-SMA and CMAr were evident in the rostral parts of the dorsal and ventral premotor cortices (PMdr and PMvr); (iv) and tracer injections into the PMdr produced neuronal cell labelling in area 46 and terminal labelling in the pre-SMA and CMAr. The present results indicate that a large portion of the prefrontal signals from area 46 is not directly conveyed to the pre-SMA and CMAr, but rather indirectly by way of the PMdr and PMvr. This suggests that area 46 exerts its major influence on the cortical motor system via these premotor areas.

Pallidal activity is involved in visuomotor association learning in monkeys.

In order to examine whether the basal ganglia are involved in arbitrary visuomotor association, we recorded neuronal activity in the internal segment of the globus pallidus (GPi) of monkeys during a conditional visuomotor learning task. Two monkeys were presented a cueing visual stimulus, and following a delay period required to push, pull or turn a manipulator according to the cue. GPi neurons showed changes in activity during the delay period when the animals performed the task on the basis of a familiar stimulus-response association. Those changes in delay activity were enhanced as the monkeys were learning a new visuomotor association. The enhancement of the changes was selective to a following response. These results suggest that the basal ganglia are involved in arbitrary visuomotor association, especially during the learning of new associations.

Neuroanatomical discrimination between manipulating and maintaining processes involved in verbal working memory; a functional MRI study.

We used functional magnetic resonance imaging (fMRI) to investigate neural correlates of processes concerning store and manipulation in verbal working memory. We prepared a revised lag 1 digit span, digit span and a simple number detection task. Specific activities in association with manipulating process were identified in the right middle (BA 9/46) and left precentral gyrus (BA 6). Activated areas specific to maintaining process were detected in the right middle (right BA 11/10) and medial (BA 6) frontal gyri, the right inferior parietal lobule (BA 40), and the left middle (BA 9) and inferior frontal gyri (BA 44). The process-nonspecific activated areas common to two processes were identified in the right inferior frontal gyrus (BA 47) and the left superior parietal lobule (BA 7). Using the signal percent change of each subject, we calculated the correlation coefficients among each activated area. The results of this analysis showed that two processes of verbal working memory were clearly discriminated. The two essential processes of manipulation and maintenance in working memory seem to activate process-specific and overlapping (process-nonspecific) areas, but the patterns of combination were definitely different.

Organization of inputs from cingulate motor areas to basal ganglia in macaque monkey.

The cingulate motor areas reside within regions lining the cingulate sulcus and are divided into rostral and caudal parts. Recent studies suggest that the rostral and caudal cingulate motor areas participate in distinct aspects of motor function: the former plays a role in higher-order cognitive control of movements, whereas the latter is more directly involved in their execution. Here, we investigated the organization of cingulate motor areas inputs to the basal ganglia in the macaque monkey. Identified forelimb representations of the rostral and caudal cingulate motor areas were injected with different anterograde tracers and the distribution patterns of labelled terminals were analysed in the striatum and the subthalamic nucleus. Corticostriatal inputs from the rostral and caudal cingulate motor areas were located within the rostral striatum, with the highest density in the striatal cell bridges and the ventrolateral portions of the putamen, respectively. There was no substantial overlap between these input zones. Similarly, a certain segregation of input zones from the rostral and caudal cingulate motor areas occurred along the mediolateral axis of the subthalamic nucleus. It has also been revealed that corticostriatal and corticosubthalamic input zones from the rostral cingulate motor area considerably overlapped those from the presupplementary motor area, while the input zones from the caudal cingulate motor area displayed a large overlap with those from the primary motor cortex. The present results indicate that a parallel design underlies motor information processing in the cortico-basal ganglia loop derived from the rostral and caudal cingulate motor areas.

Relationship between the states of spinal impact injuries and magnetically evoked EMGs in rats.

The relationship between the states of spinal impact injuries and magnetically evoked electromyograms (EMGs) were studied in rats. Impact injuries to the spinal cord were induced at a depth of 0.25-2.0 mm by insertion of a cylinder tip measuring 2 mm in diameter into the lumbar vertebrae L1-L2. Magnetically induced electromyograms for the brain and lumbar vertebrae L4-L5 were recorded from the tibialis anticus and the gastrocnemius muscles. H-reflex was not induced by the spinal cord injury (SCI) at a depth of 0.25 mm, although motor evoked potential (MEP) was observed. Continuous waves following the M-response were observed in the SCI at a depth of 0.25 mm. Elevation of the threshold, reduction of its latency and decrease in amplitude of the M-responses were observed at an injury depth of 0.5 mm or deeper. With SCI magnitude from mild (0.5 mm depth) to severe (1.0 mm depth), the amplitudes of the M-response were decreased, and the latency of the M-response was shorter than that of the control. The F-response was accelerated in severe SCI. Our results indicated that there was a relationship between extensive injury legions and the H-reflex F- and M-responses in magnetically evoked EMGs. Magnetically evoked EMGs are useful for monitoring the states of SCI.

Changes in spinal cord function caused by injuries at different levels of the lumbar spinal cord.

We examined the impact of spinal cord injury to a depth of 0.5 mm at L1-L2 (upper lumbar cord injury) and in L6-S1 (lower cord injury) in Wistar rats. Upper lumbar cord injury resulted in the disappearance of the motor evoked potential (MEP) of the gastrocnemius muscle during transcranial magnetic stimulation, while the threshold was decreased in rats with lower cord injury. During magnetic stimulation of L4-L5, the M-response threshold was decreased in rats with upper lumbar cord injury, while the amplitude was increased. In lower cord injury, the pattern of H-response recruitment curves differed from that in controls. Our results indicated that MEP and the spinal reflex are influenced not only by upper lumbar cord injury but also by lower cord injury.

Organization of somatic motor inputs from the frontal lobe to the pedunculopontine tegmental nucleus in the macaque monkey.

To reveal the somatotopy of the pedunculopontine tegmental nucleus that functions as a brainstem motor center, we examined the distribution patterns of corticotegmental inputs from the somatic motor areas of the frontal lobe in the macaque monkey. Based on the somatotopical map prepared by intracortical microstimulation, injections of the anterograde tracers, biotinylated dextran amine and wheat germ agglutinin-conjugated horseradish peroxidase, were made into the following motor-related areas: the primary motor cortex, the supplementary and presupplementary motor areas, the dorsal and ventral divisions of the premotor cortex, and the frontal eye field. Data obtained from the present experiments were as follows: (i) Corticotegmental inputs from orofacial, forelimb, and hindlimb representations of the primary motor cortex tended to be arranged orderly from medial to lateral in the pedunculopontine tegmental nucleus. However, the distribution areas of these inputs considerably overlapped; (ii) The major input zones from distal representations of the forelimb and hindlimb regions of the primary motor cortex were located medial to those from their proximal representations, although there was a substantial overlap between the distribution areas of distal versus proximal limb inputs; (iii) The main terminal zones from the forelimb regions of the primary motor cortex, the supplementary and presupplementary motor areas, and the dorsal and ventral divisions of the premotor cortex appeared to overlap largely in the mediolaterally middle aspect of the pedunculopontine tegmental nucleus; and (iv) Corticotegmental input from the frontal eye field was scattered over the pedunculopontine tegmental nucleus.Thus, the present results indicate that the pedunculopontine tegmental nucleus is likely to receive partly separate but essentially convergent cortical inputs not only from multiple motor-related areas representing the same body part, but also from multiple regions representing diverse body parts. This suggests that somatotopical representations are intermingled rather than segregated in the pedunculopontine tegmental nucleus.

Protection against dopaminergic nigrostriatal cell death by excitatory input ablation.

The importance of enhanced glutamatergic neurotransmission in the basal ganglia and related structures has recently been highlighted in the development of Parkinson's disease. The pedunculopontine tegmental nucleus (PPN) is the major origin of excitatory, glutamatergic input to dopaminergic nigrostriatal neurons of which degeneration is well known to cause Parkinson's disease. Based on the concept that an excitatory mechanism mediated by glutamatergic neurotransmission underlies the pathogenesis of neurodegenerative disorders, we made an attempt to test the hypothesis that removal of the glutamatergic input to the nigrostriatal neurons by PPN lesions might prevent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism in the macaque monkey. The PPN was lesioned unilaterally with microinjection of kainic acid, and, then, MPTP was administered systemically. In these monkeys, the degree of parkinsonian motor signs was behaviourally evaluated, and the histological changes in the dopaminergic nigrostriatal system were analysed by means of tyrosine hydroxylase immunohistochemistry. The present results revealed that nigrostriatal cell loss and parkinsonian motor deficits were largely attenuated in the MPTP-treated monkey group whose PPN had been lesioned, compared with the control, MPTP-treated monkey group with the PPN intact. This clearly indicates that the onset of MPTP neurotoxicity is suppressed or delayed by experimental ablation of the glutamatergic input to the nigrostriatal neurons. Such a protective action of excitatory input ablation against nigrostriatal cell death defines evidence that nigral excitation driven by the PPN may be implicated in the pathophysiology of Parkinson's disease.

Corticostriatal and corticosubthalamic input zones from the presupplementary motor area in the macaque monkey: comparison with the input zones from the supplementary motor area.

The presupplementary motor area (pre-SMA) is a cortical motor-related area which lies in the medial wall of the frontal lobe, immediately anterior to the supplementary motor area (SMA). This area has been considered to participate in the control of complex forelimb movements in a way different from the SMA. In an attempt to analyze the patterns of projections from the pre-SMA to the basal ganglia, we examined the distributions of pre-SMA inputs in the striatum and the subthalamic nucleus and compared them with the SMA input distributions. To detect morphologically the terminal fields from the pre-SMA and the forelimb region of the SMA, anterograde tracers were injected into such areas that had been identified electrophysiologically in the macaque monkey. Corticostriatal inputs from the pre-SMA were distributed mainly in the striatal cell bridges connecting the rostral aspects of the caudate nucleus and the putamen, as well as in their neighboring striatal portions. These input zones were located, with no substantial overlap, rostral to corticostriatal input zones from the SMA forelimb region. Corticosubthalamic input zones from the pre-SMA were almost localized in the medial aspect of the nucleus, where corticosubthalamic inputs from the SMA forelimb region were also distributed predominantly. However, the major terminal fields from the pre-SMA were centered ventrally to those from the SMA. The present results indicate that the corticostriatal and corticosubthalamic input zones from the pre-SMA appear to be segregated from the SMA-derived input zones. This implies the possibility of parallel processing of motor information from the pre-SMA and SMA in the cortico-basal ganglia circuit.

Pallidal and cerebellar inputs to thalamocortical neurons projecting to the supplementary motor area in Macaca fuscata: a triple-labeling light microscopic study.

We investigated the interrelationship between the supplementary motor area (SMA) thalamocortical projection neurons and the pallidothalamic and cerebellothalamic territories in the monkey (Macaca fuscata) using a combination of three tracers in a triple labeling paradigm. Thalamic labeling was analyzed following injections of the anterograde tracers, biotinylated dextran amine (BDA) into the internal segment of the globus pallidus (GPi) and wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the contralateral cerebellar interpositus and dentate nuclei. In addition, the retrograde tracer cholera toxin subunit B (CTB) was injected into the physiologically identified hand/arm representation of SMA. The tissue was processed sequentially using different chromogens in order to visualize all three tracers in a single section. We found that the SMA thalamocortical neurons occupied a wide band extending from the ventral anterior nucleus pars principalis (VApc) through the ventral lateral nucleus pars oralis (VLo) and the ventral lateral nucleus pars medialis (VLm) and into to the ventral lateral nucleus pars caudalis (VLc) including a portion of ventral posterior lateral nucleus pars oralis (VPLo) and nucleus X. The heaviest CTB labeling was found in VLo with dense plexuses of BDA labeled pallidothalamic fibers and swellings often observed superimposed upon retrogradely labeled CTB cells. In addition, dense foci of cerebellothalamic WGA-HRP anterograde label were observed coinciding with the occasional retrogradely CTB labeled neurons in VLc and transitional zones between VApc, VLo and VPLo. Our light microscopic results suggest that the SMA receives thalamic inputs with afferents largely derived from GPi and minor inputs originating from the cerebellum.

Corticostriatal projections from distal and proximal forelimb representations of the monkey primary motor cortex.

Corticostriatal projections from one distal and two proximal subregions in the forelimb representation of the primary motor cortex (MI) were examined in the macaque monkey. The distal and proximal subregions in the anterior bank of the central sulcus (distal and proximal-bank subregions) and the proximal subregion in the surface of the precentral gyrus (proximal-surface subregion) of the MI were identified using intracortical microstimulation. Different anterograde tracers were then injected into two of these three forelimb subregions of the MI. In the ipsilateral putamen, the distribution areas of corticostriatal fibers from the distal, proximal-bank and proximal-surface subregions were arranged from ventrolateral to dorsomedial in this order. These corticostriatal input zones were largely segregated from one another.

Morphology of thyroid vascular casts of hypertensive rats.

Thyroid vascular casts were made by injecting a resin, Mercox, into 3 types of hypertensive rats (spontaneously hypertensive rats, SHR, stroke-prone SHR, SHRSP, malignant SHRSP, M-SHRSP), and the vascular casts were observed by scanning electron microscopy (SEM). There was no difference in the general morphology of the vascular casts between SHR and the control (Wistar Kyoto rats, WKY). However, the density and the diameter of blood vessels in SHRSP and M-SHRSP were significantly different from those in WKY, and abnormal vasculatures that formed protrusions with free endings were observed in M-SHRSP. It was concluded that thyroid vascular networks in hypertensive rats were transformed into abnormal formations with decreased capillary diameter in parallel with the progress of hypertension.

Corticostriatal projections from the somatic motor areas of the frontal cortex in the macaque monkey: segregation versus overlap of input zones from the primary motor cortex, the supplementary motor area, and the premotor cortex.

It is an important issue to address the mode of information processing in the somatic motor circuit linking the frontal cortex and the basal ganglia. In the present study, we investigated the extent to which corticostriatal input zones from the primary motor cortex (MI), the supplementary motor area (SMA), and the premotor cortex (PM) of the macaque monkey might overlap in the putamen. Intracortical microstimulation was performed to map the MI, SMA, and dorsal (PMd) and ventral (PMv) divisions of the PM. Then, two different anterograde tracers were injected separately into somatotopically corresponding regions of two given areas of the MI, SMA, PMd, and PMv. With respect to the PMd and PMv, tracer injections were centered on their forelimb representations. Corticostriatal input zones from hindlimb, forelimb, and orofacial representations of the MI and SMA were, in this order, arranged from dorsal to ventral within the putamen. Dense input zones from the MI were located predominantly in the lateral aspect of the putamen, whereas those from the SMA were in the medial aspect of the putamen. On the other hand, corticostriatal inputs from forelimb representations of the PMd and PMv were distributed mainly in the dorsomedial sector of the putamen. Thus, the corticostriatal input zones from the MI and SMA were considerably segregated though partly overlapped in the mediolateral central aspect of the putamen, while the corticostriatal input zone from the PM largely overlapped that from the SMA, but not from the MI.

Corticostriatal input zones from the supplementary motor area overlap those from the contra- rather than ipsilateral primary motor cortex.

To investigate the degree of convergence of corticostriatal inputs from the primary motor cortex (MI) and the supplementary motor area (SMA), we analyzed the extent to which corticostriatal inputs from forelimb representations of these motor-related areas spatially overlap in the macaque monkey. Of particular interest was that corticostriatal input zones from SMA overlapped those from MI of the contralateral hemisphere more extensively than from MI of the ipsilateral hemisphere.

Reevaluation of ipsilateral corticocortical inputs to the orofacial region of the primary motor cortex in the macaque monkey.

An anatomical approach to possible areas in the cerebral cortex involved in somatic motor behavior is to analyze the cortical areas containing neurons that connect directly to the primary motor cortex (MI). To define the cortical areas related to orofacial movements, we examined the distribution of cortical neurons that send their axons to the orofacial region of the MI in the macaque monkey. Injections of retrograde tracers into the electrophysiologically identified orofacial region of the MI revealed that labeled neurons were distributed in the following cortical areas: the orbital cortex (area 12), insular cortex, frontoparietal operculum (including the deep part of the cortical masticatory area and the secondary somatosensory cortex), ventral division of the premotor cortex (especially in its lateral part), orofacial region of the supplementary motor area, rostral division of the cingulate motor area (CMA), and CMA on the ventral bank. A number of labeled neurons were also seen in the MI around the injection sites and in the parietal cortex (including the primary somatosensory cortex and area 7b). No labeled neurons were found in the dorsal division of the premotor cortex. Fluorescent retrograde double labeling further revealed virtually no overlap of distribution between cortical neurons projecting to the orofacial and forelimb regions of the MI. Based on the present results, we discuss the functional diversity of the cortical areas related to orofacial motor behavior and the somatotopical organization in the premotor areas of the frontal cortex.

Excitotoxic lesions of the pedunculopontine tegmental nucleus produce contralateral hemiparkinsonism in the monkey.

Dopaminergic nigrostriatal neurons, degeneration of which causes Parkinson's disease, are known to receive excitatory input almost exclusively from the pedunculopontine tegmental nucleus (PPN). We report here that excitotoxic lesions of the PPN produce abnormal motor signs relevant to hemiparkinsonism in the macaque monkey. Under the guidance of extracellular unit recordings, the electrophysiologically identified PPN was injected unilaterally with kainic acid. These PPN-lesioned monkeys exhibited mild to moderate levels of flexed posture and hypokinesia in the upper and lower limbs contralateral to the lesion. In most of the monkeys, such pathophysiological events were gradually improved and became stationary in 1-2 weeks. The hemiparkinsonian symptoms observed after PPN destruction might be ascribed to a decrease in nigrostriatal neuron activity due to excitatory input ablation.

Dopaminergic modulation of neuronal activity in the monkey putamen through D1 and D2 receptors during a delayed Go/Nogo task.

Using multibarreled glass micropipettes, we recorded single-unit activity in the putamen, and iontopho retically applied D1 and D2 dopamine receptor agonists (SKF38393, quinpirole) and antagonists (SCH23390, sulpiride) while two monkeys were performing a delayed Go/Nogo task. The putaminal neurons exhibited changes in activity during various task periods (hold, cue, delay, response, and reward periods) in both Go and Nogo trials. Of 296 task-related putaminal neurons, 87 showed activity changes in Go trials only (Go type), 74 in Nogo trials only (Nogo type), 99 in both trials during the same task periods (Both type), and 36 in both trials but during different task periods (Different type). These 296 neurons were examined as regards the effects of both D1 and D2 agonists and/or antagonists, and 234 neurons responded to either D1 - or D2-related substances or both. Among them 41% of neurons responded to the D1 substances only (D1 group), 36% responded to the D2 substances only (D2 group), and 23% responded to both D1 and D2 substances (D1D2 group). During the iontophoretic application of the D1 and D2 substances, most of the responding neurons changed their task-related activity but not their baseline firing rates. The D1 agonist increased the activity in 19 neurons and decreased it in 105 neurons. On the other hand, the D2 agonist increased the activity in 54 neurons and decreased it in 50 neurons. The D1 and D2 substances modulated the activity in both Go and Nogo trials. Each of the three D1/D2 groups (D1, D2, and D1D2 groups) contained all four Go/Nogo types (Go, Nogo, Both, and Different types) of neurons. Percentages of each Go/Nogo type of neuron were comparable among the three D1/D2 groups. The D1 and D2 substances modulated the activity related to various task periods. Each of the three D1/D2 groups included neurons activated during the cue, delay, response, or reward period in Go and Nogo trials. Distributions of the neurons related to each task period were similar among the D1/D2 groups. These results suggest that dopamine can modulate the activity of single putaminal neurons through both D1 and D2 receptors and that the dopaminergic modulation through the two receptors in the putamen affects similar types of signals in behavioral control.

Corticosubthalamic input zones from forelimb representations of the dorsal and ventral divisions of the premotor cortex in the macaque monkey: comparison with the input zones from the primary motor cortex and the supplementary motor area.

Employing double anterograde axonal tracing in combination with intracortical microstimulation, we examined the distribution patterns of corticosubthalamic inputs from forelimb representations of the dorsal (PMd) and ventral (PMv) divisions of the premotor cortex in the macaque monkey. The inputs from the PMd and PMv were distributed mainly in the medial aspect of the subthalamic nucleus (STN), in which their distribution areas overlapped each other. By the same experimental approach, we further compared corticosubthalamic input zones from the PMd/PMv with those from the primary motor cortex (MI) and the supplementary motor area (SMA). The input zones from the PMd/PMv and SMA largely overlapped in the medial aspect of the STN, whereas the input zones from the PMd/PMv and MI were virtually segregated mediolaterally in the STN.