Theoretical proposal for restoration of hand motor function based on plasticity of motor-cortical interhemispheric interaction and its developmental rule.

After stroke, the poorer recovery of motor function of upper extremities compared to other body parts is a longstanding problem. Based on our recent functional MRI evidence on healthy volunteers, this perspective paper proposes systematic hand motor rehabilitation utilizing the plasticity of interhemispheric interaction between motor cortices and following its developmental rule. We first discuss the effectiveness of proprioceptive intervention on the paralyzed (immobile) hand synchronized with voluntary movement of the intact hand to induce muscle activity in the paretic hand. In healthy participants, we show that this bilateral proprioceptive-motor coupling intervention activates the bilateral motor cortices (= bilaterally active mode), facilitates interhemispheric motor-cortical functional connectivity, and augments muscle activity of the passively-moved hand. Next, we propose training both hands to perform different movements, which would be effective for stroke patients who becomes able to manage to move the paretic hand. This bilaterally different movement training may guide the motor cortices into left-right independent mode to improve interhemispheric inhibition and hand dexterity, because we have shown in healthy older adults that this training reactivates motor-cortical interhemispheric inhibition (= left-right independent mode) declined with age, and can improve hand dexterity. Transition of both motor cortices from the bilaterally active mode to the left-right independent mode is a developmental rule of hand motor function and a common feature of motor function recovery after stroke. Hence, incorporating the brain's inherent capacity for spontaneous recovery and adhering to developmental principles may be crucial considerations in designing effective rehabilitation strategies.

Volume electron microscopy analysis of synapses in primary regions of the human cerebral cortex.

Functional and structural studies investigating macroscopic connectivity in the human cerebral cortex suggest that high-order associative regions exhibit greater connectivity compared to primary ones. However, the synaptic organization of these brain regions remains unexplored. In the present work, we conducted volume electron microscopy to investigate the synaptic organization of the human brain obtained at autopsy. Specifically, we examined layer III of Brodmann areas 17, 3b, and 4, as representative areas of primary visual, somatosensorial, and motor cortex. Additionally, we conducted comparative analyses with our previous datasets of layer III from temporopolar and anterior cingulate associative cortical regions (Brodmann areas 24, 38, and 21). 9,690 synaptic junctions were 3D reconstructed, showing that certain synaptic characteristics are specific to particular regions. The number of synapses per volume, the proportion of the postsynaptic targets, and the synaptic size may distinguish one region from another, regardless of whether they are associative or primary cortex. By contrast, other synaptic characteristics were common to all analyzed regions, such as the proportion of excitatory and inhibitory synapses, their shapes, their spatial distribution, and a higher proportion of synapses located on dendritic spines. The present results provide further insights into the synaptic organization of the human cerebral cortex.

Sensory and motor cortices parcellations estimated via distance-weighted sparse representation with application to autism spectrum disorder.

BACKGROUND: Motor impairments and sensory processing abnormalities are prevalent in autism spectrum disorder (ASD), closely related to the core functions of the primary motor cortex (M1) and the primary somatosensory cortex (S1). Currently, there is limited knowledge about potential therapeutic targets in the subregions of M1 and S1 in ASD patients. This study aims to map clinically significant functional subregions of M1 and S1. METHODS: Resting-state functional magnetic resonance imaging data (NTD = 266) from Autism Brain Imaging Data Exchange (ABIDE) were used for subregion modeling. We proposed a distance-weighted sparse representation algorithm to construct brain functional networks. Functional subregions of M1 and S1 were identified through consensus clustering at the group level. Differences in the characteristics of functional subregions were analyzed, along with their correlation with clinical scores. RESULTS: We observed symmetrical and continuous subregion organization from dorsal to ventral aspects in M1 and S1, with M1 subregions conforming to the functional pattern of the motor homunculus. Significant intergroup differences and clinical correlations were found in the dorsal and ventral aspects of M1 (p < 0.05/3, Bonferroni correction) and the ventromedial BA3 of S1 (p < 0.05/5). These functional characteristics were positively correlated with autism severity. All subregions showed significant results in the ROI-to-ROI intergroup differential analysis (p < 0.05/80). LIMITATIONS: The generalizability of the segmentation model requires further evaluation. CONCLUSIONS: This study highlights the significance of M1 and S1 in ASD treatment and may provide new insights into brain parcellation and the identification of therapeutic targets for ASD.

Visual effects on tactile stimulation and its perception: A pilot study using near-infrared spectroscopy.

In rubber hand illusion, visual information affects tactile information, whereas in the mirror box illusion, visual information has the opposite effect. However, its underlying mechanisms are not fully understood. As one of the reasons, non-invasive neuroimaging techniques, such as functional magnetic resonance, positron emission tomography, and electroencephalography, often fail to detect complex and fragile responses in the sensory-motor cortex. Using near-infrared spectroscopy (NIRS), we examined neural activity during tactile tracing on a sine-shaped acrylic board to investigate the effects of (1) visual information and (2) the spatial frequency of the sine shape on brain activity. We used spatial frequencies of 2-3 and 20-30 Hz as low- and high-tactile stimuli, respectively. Two types of experiments, with and without an acrylic board, were conducted. Participants performed the tracing tasks with their index finger at 1 Hz of temporal frequency of a 200 mm length of the acrylic board as main tasks and only space moving without touching as a control task. We show effect of visual information on neural activation, including not only activation intensity but also activation patterns.•Testing of mutual effects of vision and haptics.•Testing of sensory-motor paradox using NIRS.•A high NIRS sensitivity to stimulus-induced hemodynamic change.

Regular cannabis use modulates gamma activity in brain regions serving motor control.

BACKGROUND: People who regularly use cannabis exhibit altered brain dynamics during cognitive control tasks, though the impact of regular cannabis use on the neural dynamics serving motor control remains less understood. AIMS: We sought to investigate how regular cannabis use modulates the neural dynamics serving motor control. METHODS: Thirty-four people who regularly use cannabis (cannabis+) and 33 nonusers (cannabis-) underwent structured interviews about their substance use history and performed the Eriksen flanker task to map the neural dynamics serving motor control during high-density magnetoencephalography (MEG). The resulting neural data were transformed into the time-frequency domain to examine oscillatory activity and were imaged using a beamforming approach. RESULTS: MEG sensor-level analyses revealed robust beta (16-24 Hz) and gamma oscillations (66-74 Hz) during motor planning and execution, which were imaged using a beamformer. Both responses peaked in the left primary motor cortex and voxel time series were extracted to evaluate the spontaneous and oscillatory dynamics. Our key findings indicated that the cannabis+ group exhibited weaker spontaneous gamma activity in the left primary motor cortex relative to the cannabis- group, which scaled with cannabis use and behavioral metrics. Interestingly, regular cannabis use was not associated with differences in oscillatory beta and gamma activity, and there were no group differences in spontaneous beta activity. CONCLUSIONS: Our findings suggest that regular cannabis use is associated with suppressed spontaneous gamma activity in the left primary motor cortex, which scales with the degree of cannabis use disorder symptomatology and is coupled to behavioral task performance.

Motor cortex is responsible for motoric dynamics in striatum and the execution of both skilled and unskilled actions.

Striatum and its predominant input, motor cortex, are responsible for the selection and performance of purposive movement, but how their interaction guides these processes is not understood. To establish its neural and behavioral contributions, we bilaterally lesioned motor cortex and recorded striatal activity and reaching performance daily, capturing the lesion's direct ramifications within hours of the intervention. We observed reaching impairment and an absence of striatal motoric activity following lesion of motor cortex, but not parietal cortex control lesions. Although some aspects of performance began to recover after 8-10 days, striatal projection and interneuronal dynamics did not-eventually entering a non-motor encoding state that aligned with persisting kinematic control deficits. Lesioned mice also exhibited a profound inability to switch motor plans while locomoting, reminiscent of clinical freezing of gait (FOG). Our results demonstrate the necessity of motor cortex in generating trained and untrained actions as well as striatal motoric dynamics.

The effect of resection of gliomas of the primary motor and sensory cortex on functional recovery and seizure outcome: A 10-year retrospective study.

Background: Gliomas, the most common primary brain tumors, pose surgical challenges in eloquent cortex regions due to potential deficits affecting patients' quality of life (QOL) and increased mortality risk. This study investigates motor and sensory recovery postresection of Rolandic cortex gliomas in 40 patients, alongside seizure outcomes and the efficacy of intraoperative techniques such as awake craniotomy. Methods: This was a 10-year monocentric retrospective study based on the experience of a neurosurgeon in the resection of Rolandic gliomas and its impact on 40 patients' QOL in a period from 2011 to 2020. The primary outcomes were tumor recurrence and the efficacy of the surgery defined as survival status, seizure status, and sensory and motor neurological deficits. Data collection included demographic, tumor, and surgical outcome variables. The extent of resection (EOR) was classified as gross total resection (GTR) (EOR ≥95%) or subtotal resection (EOR <95%). Statistical analysis involved descriptive statistics and inferential tests for outcome comparisons. Results: Patients were aged an average of 42.3 ± 14 years and distributed between 72.5% of males and 27.5% of females. The most common presentation was seizures (65%). The tumor was located in the frontal lobe at 65%, the motor at 75%, and the top tumor pathology was oligodendroglioma (42.5%). The recurrence rate in the study was 20% (8 of 40), and the 1-year survival rate was 92.5%. After the resection, significant improvement was shown in Karnofsky's performance status (P = 0.007), in normal daily activities (P = 0.001), in fine motor skills (P = 0.020), and work hobbies (P = 0.046). No statistically significant improvement was shown in seizures and deficit rates. Recurrence was not associated with the demographic characteristics, clinical presentation, tumor-related characteristics (location, area, side, and mutation), tumor resection, and adjuvant treatment (P > 0.05). Conclusion: GTR of Rolandic gliomas can be achieved with the use of meticulous stimulation mapping, and complete functional recovery is attainable despite common belief.

Cortical activation in REM behavior disorder mimics voluntary movement. An electroencephalography study.

OBJECTIVES: Motor symptoms of Parkinson's disease improve during REM sleep behavior disorder movement episodes. Our aim was to study cortical activity during these movement episodes, in patients with and without Parkinson's disease, in order to investigate the cortical involvement in the generation of its electromyographic activity and its potential relationship with Parkinson's disease. METHODS: We looked retrospectively in our polysomnography database for patients with REM sleep behavior disorder, analyzing fifteen patients in total, seven with idiopathic REM sleep behavior disorder and eight associated with Parkinson's disease. We selected segments of REM sleep with the presence of movements (evidenced by electromyographic activation), and studied movement-related changes in cortical activity by averaging the electroencephalographic signal (premotor potential) and by means of time/frequency transforms. RESULTS: We found a premotor potential and an energy decrease of alpha-beta oscillatory activity preceding the onset of electromyographic activity, together with an increase of gamma activity for the duration of the movement. All these changes were similarly present in REM sleep behavior disorder patients with and without Parkinson's disease. CONCLUSIONS: Movement-related changes in electroencephalographic activity observed in REM sleep behavior disorder are similar to those observed during voluntary movements, regardless of the presence of Parkinson's disease motor symptoms. SIGNIFICANCE: These results suggest a main involvement of the cortex in the generation of the movements during REM sleep.

Repeated spaced cortical paired associative stimulation promotes additive plasticity in the human parietal-motor circuit.

OBJECTIVE: Repeated spaced sessions of repetitive transcranial magnetic stimulation (TMS) to the human primary motor cortex can lead to dose-dependent increases in motor cortical excitability. However, this has yet to be demonstrated in a defined cortical circuit. We aimed to examine the effects of repeated spaced cortical paired associative stimulation (cPAS) on excitability in the motor cortex. METHODS: cPAS was delivered to the primary motor cortex (M1) and posterior parietal cortex (PPC) with two coils. In the multi-dose condition, three sessions of cPAS were delivered 50-min apart. The single-dose condition had one session of cPAS, followed by two sessions of a control cPAS protocol. Motor-evoked potentials were evaluated before and up to 40 min after each cPAS session as a measure of cortical excitability. RESULTS: Compared to a single dose of cPAS, motor cortical excitability significantly increased after multi-dose cPAS. Increasing the number of cPAS sessions resulted in a cumulative, dose-dependent effect on excitability in the motor cortex, with each successive cPAS session leading to notable increases in potentiation. CONCLUSION: Repeated spaced cPAS sessions summate to increase motor cortical excitability induced by single cPAS. SIGNIFICANCE: Repeated spaced cPAS could potentially restore abilities lost due to disorders like stroke.

Investigating brain structure and tDCS response in obsessive-compulsive disorder.

Obsessive-Compulsive Disorder (OCD) is characterized by intrusive thoughts and repetitive behaviors, with associated brain abnormalities in various regions. This study explores the correlation between neural biomarkers and the response to transcranial Direct Current Stimulation (tDCS) in OCD patients. Using structural MRI data from two tDCS trials involving 55 OCD patients and 28 controls, cortical thickness, and gray matter morphometry was analyzed. Findings revealed thicker precentral and paracentral areas in OCD patients, compared to control (p < 0.001). Correlations between cortical thickness and treatment response indicated a significant association between a thinner precentral area and reduced Yale-Brown Obsessive Compulsive Scale (YBOCS) scores (p = 0.02). While results highlight the complexity of treatment response predictors, this study sheds light on potential neural markers for tDCS response in OCD patients. Further investigations with larger datasets are warranted to better understand the underpinnings of these biomarkers and their implications for personalized treatment approaches.

The effects of combining sensorimotor training with transcranial direct current stimulation on the anticipatory and compensatory postural adjustments in patients with chronic low back pain.

PURPOSE: To investigate the effects of concurrent sensorimotor training (SMT) and transcranial direct current stimulation (tDCS) on the anticipatory and compensatory postural adjustments (APAs and CPAs) in patients with chronic low back pain (CLBP). METHOD: The interventions included (1) SMT plus tDCS and (2) SMT plus sham tDCS. Outcome measures were the normalized integrals of electromyography activity (NIEMG) during the phases of anticipatory and compensatory, and muscle onset latency. The investigated muscles were ipsilateral and contralateral multifidus (MF), transversus abdominus/internal oblique (TrA/IO), and gluteus medius (GM). RESULTS: Between-group comparisons demonstrated that ipsilateral TrA/IO NIEMG during CPA1 (p = 0.010) and ipsilateral GM NIEMG during CPA1 (p = 0.002) and CPA2 (p = 0.025) were significantly lower in the SMT combined with tDCS than in the control group. Furthermore, this group had greater NIEMG for contralateral GM during APA1 than the control group (p = 0.032). Moreover, the onset latency of contralateral TrA/IO was significantly earlier after SMT combined with tDCS (p = 0.011). CONCLUSIONS: Both groups that received SMT showed positive effects, but anodal tDCS had an added value over sham stimulation for improving postural control strategies in patients with CLBP. Indeed, SMT combined with tDCS leads to stronger APA and less demand for CPA. RCT REGISTRATION NUMBER: IRCT20220228054149N1. REGISTRATION DATE: 2022-04-04.

Evidence suggests that reduced excitability in the sensory and motor cortex is linked to chronic and recurring lower back pain.Increasing the excitability of these two areas using anodal transcranial direct current stimulation (tDCS), in conjunction with sensorimotor training (SMT), may improve anticipatory and compensatory postural control strategies.This study showed that the combination of SMT with tDCS targeting the sensory and motor cortex notably enhances motor preparation and refines postural control strategies in patients with chronic unilateral lumbar radiculopathy.Rehabilitation professionals are encouraged to integrate SMT with tDCS into treatment protocols to enhance the ability of individuals with back pain to handle postural disturbances in daily life, thereby potentially alleviating the persistence of their symptoms.Incorporating brain stimulation enhances the effectiveness of SMT for patients with chronic unilateral lumbar radiculopathy.

Sex differences in motor learning flexibility are accompanied by sex differences in mushroom spine pruning of the mouse primary motor cortex during adolescence.

Background: Although males excel at motor tasks requiring strength, females exhibit greater motor learning flexibility. Cognitive flexibility is associated with low baseline mushroom spine densities achieved by pruning which can be triggered by α4ßδ GABAA receptors (GABARs); defective synaptic pruning impairs this process. Methods: We investigated sex differences in adolescent pruning of mushroom spine pruning of layer 5 pyramidal cells of primary motor cortex (L5M1), a site essential for motor learning, using microscopic evaluation of Golgi stained sections. We assessed α4GABAR expression using immunohistochemical and electrophysiological techniques (whole cell patch clamp responses to 100 nM gaboxadol, selective for α4ßδ GABARs). We then compared performance of groups with different post-pubertal mushroom spine densities on motor learning (constant speed) and learning flexibility (accelerating speed following constant speed) rotarod tasks. Results: Mushroom spines in proximal L5M1 of female mice decreased >60% from PND35 (puberty onset) to PND56 (Pubertal: 2.23 ± 0.21 spines/10 µm; post-pubertal: 0.81 ± 0.14 spines/10 µm, P < 0.001); male mushroom spine density was unchanged. This was due to greater α4ßδ GABAR expression in the female (P < 0.0001) because α4 -/- mice did not exhibit mushroom spine pruning. Although motor learning was similar for all groups, only female wild-type mice (low mushroom spine density) learned the accelerating rotarod task after the constant speed task (P = 0.006), a measure of motor learning flexibility. Conclusions: These results suggest that optimal motor learning flexibility of female mice is associated with low baseline levels of post-pubertal mushroom spine density in L5M1 compared to male and female α4 -/- mice.

Cholinergic modulation of interhemispheric inhibition in the mouse motor cortex.

Interhemispheric inhibition of the homotopic motor cortex is believed to be effective for accurate unilateral motor function. However, the cellular mechanisms underlying interhemispheric inhibition during unilateral motor behavior remain unclear. Furthermore, the impact of the neuromodulator acetylcholine on interhemispheric inhibition and the associated cellular mechanisms are not well understood. To address this knowledge gap, we conducted recordings of neuronal activity from the bilateral motor cortex of mice during the paw-reaching task. Subsequently, we analyzed interhemispheric spike correlation at the cell-pair level, classifying putative cell types to explore the underlying cellular circuitry mechanisms of interhemispheric inhibition. We found a cell-type pair-specific enhancement of the interhemispheric spike correlation when the mice were engaged in the reaching task. We also found that the interhemispheric spike correlation was modulated by pharmacological acetylcholine manipulation. The local field responses to contralateral excitation differed along the cortical depths, and muscarinic receptor antagonism enhanced the inhibitory component of the field response in deep layers. The muscarinic subtype M2 receptor is predominantly expressed in deep cortical neurons, including GABAergic interneurons. These results suggest that GABAergic interneurons expressing muscarinic receptors in deep layers mediate the neuromodulation of interhemispheric inhibition in the homotopic motor cortex.

Electroacupuncture alleviates motor dysfunction by regulating neuromuscular junction disruption and neuronal degeneration in SOD1G93A mice.

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disease characterized by the progressive destruction of the neuromuscular junction (NMJ) and the degeneration of motor neurons, eventually leading to atrophy and paralysis of voluntary muscles responsible for motion and breathing. NMJs, synaptic connections between motor neurons and skeletal muscle fibers, are extremely fragile in ALS. To determine the effects of early electroacupuncture (EA) intervention on nerve reinnervation and regeneration following injury, a model of sciatic nerve injury (SNI) was first established using SOD1G93A mice, and early electroacupuncture (EA) intervention was conducted at Baihui (DU20), and bilateral Zusanli (ST36). The results revealed that EA increased the Sciatic nerve Functional Index, the structural integrity of the gastrocnemius muscles, and the cross-sectional area of muscle fibers, as well as up-regulated the expression of acetylcholinesterase and facilitated the co-location of α7 nicotinic acetate choline receptors and α-actinin. Overall, these results suggested that EA can promote the repair and regeneration of injured nerves and delay NMJ degeneration in SOD1G93A-SNI mice. Moreover, analysis of the cerebral cortex demonstrated that EA alleviated cortical motor neuron damage in SOD1G93A mice, potentially attributed to the inhibition of the cyclic GMP-AMP synthase-stimulator of interferon genes pathway and the release of interferon-ß suppressing the activation of natural killer cells and the secretion of interferon-γ, thereby further inhibiting microglial activation and the expression of inflammatory factors. In summary, EA delayed the degeneration of NMJ and mitigated the loss of cortical motor neurons, thus delaying disease onset, accompanied by alleviation of muscle atrophy and improvements in motor function in SOD1G93A mice.

Investigating the Effects of Repetitive Paired-Pulse Transcranial Magnetic Stimulation on Visuomotor Training Using TMS-EEG.

I-wave periodicity repetitive paired-pulse transcranial magnetic stimulation (iTMS) can modify acquisition of a novel motor skill, but the associated neurophysiological effects remain unclear. The current study therefore used combined TMS-electroencephalography (TMS-EEG) to investigate the neurophysiological effects of iTMS on subsequent visuomotor training (VT). Sixteen young adults (26.1 ± 5.1 years) participated in three sessions including real iTMS and VT (iTMS + VT), control iTMS and VT (iTMSControl + VT), or iTMS alone. Motor-evoked potentials (MEPs) and TMS-evoked potentials (TEPs) were measured before and after iTMS, and again after VT, to assess neuroplastic changes. Irrespective of the intervention, MEP amplitude was not changed after iTMS or VT. Motor skill was improved compared with baseline, but no differences were found between stimulus conditions. In contrast, the P30 peak was altered by VT when preceded by control iTMS (P < 0.05), but this effect was not apparent when VT was preceded by iTMS or following iTMS alone (all P > 0.15). In contrast to expectations, iTMS was unable to modulate MEP amplitude or influence motor learning. Despite this, changes in P30 amplitude suggested that motor learning was associated with altered cortical reactivity. Furthermore, this effect was abolished by priming with iTMS, suggesting an influence of priming that failed to impact learning.

Motor cortex activation mediates associations between striatal dopamine depletion and manual dexterity in Parkinson's disease.

INTRODUCTION: Parkinson's disease (PD) presents with a progressive decline in manual dexterity, attributed to dysfunction in the basal ganglia-thalamus-cortex loop, influenced by dopaminergic deficits in the striatum. Recent research suggests that the motor cortex may play a pivotal role in mediating the relationship between striatal dopamine depletion and motor function in PD. Understanding this connection is crucial for comprehending the origins of manual dexterity impairments in PD. Therefore, our study aimed to explore how motor cortex activation mediates the association between striatal dopamine depletion and manual dexterity in PD. MATERIALS AND METHODS: We enrolled 26 mildly affected PD patients in their off-medication phase to undergo [18F]FDOPA PET/CT scans for evaluating striatal dopaminergic function. EEG recordings were conducted during bimanual anti-phase finger tapping tasks to evaluate motor cortex activity, specifically focusing on Event-Related Desynchronization in the beta band. Manual dexterity was assessed using the Purdue Pegboard Test. Regression-based mediation analysis was conducted to examine whether motor cortex activation mediates the association between striatal dopamine depletion and manual dexterity in PD. RESULTS: Mediation analysis revealed a significant direct effect of putamen dopamine depletion on manual dexterity for the affected hand and assembly tasks (performed with two hands), with motor cortex activity mediating this association. In contrast, while caudate nucleus dopamine depletion showed a significant direct effect on manual dexterity, motor cortex mediation on this association was not observed. CONCLUSION: Our study confirms the association between striatum dopamine depletion and impaired manual dexterity in PD, with motor cortex activity mediating this relationship.

Cortico-basal ganglia plasticity in motor learning.

One key function of the brain is to control our body's movements, allowing us to interact with the world around us. Yet, many motor behaviors are not innate but require learning through repeated practice. Among the brain's motor regions, the cortico-basal ganglia circuit is particularly crucial for acquiring and executing motor skills, and neuronal activity in these regions is directly linked to movement parameters. Cell-type-specific adaptations of activity patterns and synaptic connectivity support the learning of new motor skills. Functionally, neuronal activity sequences become structured and associated with learned movements. On the synaptic level, specific connections become potentiated during learning through mechanisms such as long-term synaptic plasticity and dendritic spine dynamics, which are thought to mediate functional circuit plasticity. These synaptic and circuit adaptations within the cortico-basal ganglia circuitry are thus critical for motor skill acquisition, and disruptions in this plasticity can contribute to movement disorders.

Immersive virtual reality in orthopedic hand therapy.

Emerging advances in immersive virtual reality incorporating optical hand-tracking present promising potential for application in orthopedic hand therapy. The system is designed to analyze hand movements, enabling users to "use" their hands virtually in any fabricated setting. This article, supplemented with videos, examines practical applications of immersive virtual reality in routine hand therapy and provides a scientific presentation of the interaction of immersive virtual reality with our physiological and neurological systems. Indications for immersive virtual reality use, critical evaluations and recommendations are comprehensively discussed. Immersive virtual reality has the potential to evolve into a standard treatment modality in orthopedic hand therapy.

Functional states of prelimbic and related circuits during the acquisition of a GO/noGO task in rats.

GO/noGO tasks enable assessing decision-making processes and the ability to suppress a specific action according to the context. Here, rats had to discriminate between 2 visual stimuli (GO or noGO) shown on an iPad screen. The execution (for GO) or nonexecution (for noGO) of the selected action (to touch or not the visual display) were reinforced with food. The main goal was to record and to analyze local field potentials collected from cortical and subcortical structures when the visual stimuli were shown on the touch screen and during the subsequent activities. Rats were implanted with recording electrodes in the prelimbic cortex, primary motor cortex, nucleus accumbens septi, basolateral amygdala, dorsolateral and dorsomedial striatum, hippocampal CA1, and mediodorsal thalamic nucleus. Spectral analyses of the collected data demonstrate that the prelimbic cortex was selectively involved in the cognitive and motivational processing of the learning task but not in the execution of reward-directed behaviors. In addition, the other recorded structures presented specific tendencies to be involved in these 2 types of brain activity in response to the presentation of GO or noGO stimuli. Spectral analyses, spectrograms, and coherence between the recorded brain areas indicate their specific involvement in GO vs. noGO tasks.

Goal-directed action preparation in humans entails a mixture of corticospinal neural computations.

The seemingly effortless ability of humans to transition from thinking about actions to initiating them relies on sculpting corticospinal output from primary motor cortex. This study tested whether canonical additive and multiplicative neural computations, well-described in sensory systems, generalize to the corticospinal pathway during human action preparation. We used non-invasive brain stimulation to measure corticospinal input-output across varying action preparation contexts during instructed-delay finger response tasks. Goal-directed action preparation was marked by increased multiplicative gain of corticospinal projections to task-relevant muscles and additive suppression of corticospinal projections to non-selected and task-irrelevant muscles. Individuals who modulated corticospinal gain to a greater extent were faster to initiate prepared responses. Our findings provide physiological evidence of combined additive suppression and gain modulation in the human motor system. We propose these computations support action preparation by enhancing the contrast between selected motor representations and surrounding background activity to facilitate response selection and execution.