Organization of multisynaptic inputs from prefrontal cortex to primary motor cortex as revealed by retrograde transneuronal transport of rabies virus

Chemogenetic dissection of a prefrontal-hypothalamic circuit for socially subjective reward valuation in macaques

The value of one's own reward is affected by the reward of others, serving as a source for envy. However, it is not known which neural circuits mediate such socially subjective value modulation. Here, we chemogenetically dissected the circuit from the medial prefrontal cortex (MPFC) to the lateral hypothalamus (LH) while male macaques were presented with visual stimuli that concurrently signaled the prospects of one's own and others' rewards. We found that functional disconnection between the MPFC and LH rendered animals significantly less susceptible to others' but not one's own reward prospects. In parallel with this behavioral change, inter-areal coordination, as indexed by coherence and Granger causality, decreased primarily in the delta and theta bands. These findings demonstrate that the MPFC-to-LH circuit plays a crucial role in carrying information about upcoming other-rewards for subjective reward valuation in social contexts.

Divergent topographic projection of cerebral cortical areas to overlapping cerebellar lobules through distinct regions of the pontine nuclei

The massive axonal projection from the cerebrum to the cerebellum through the pontine nuclei supports the cerebrocerebellar coordination of motor and nonmotor functions. However, the cerebrum and cerebellum have distinct patterns of functional localization in their cortices. We addressed this issue by bidirectional neuronal tracing from 22 various locations of the pontine nuclei in the mouse in a comprehensive manner. Cluster analyses of the distribution patterns of labeled cortical pyramidal cells and cerebellar mossy fiber terminals classified all cases into six groups located in six different subareas of the pontine nuclei. The lateral (insular), mediorostral (cingulate and prefrontal), and caudal (visual and auditory) cortical areas of the cerebrum projected to the medial, rostral, and lateral subareas of the pontine nuclei, respectively. These pontine subareas then projected mainly to the crus I, central vermis, and paraflocculus divergently. The central (motor and somatosensory) cortical areas projected to the centrorostral, centrocaudal and caudal subareas of the pontine nuclei, which then projected mainly to the rostral and caudal lobules with a somatotopic arrangement. The results indicate a new pontine nuclei-centric view of the corticopontocerebellar projection: the generally parallel corticopontine projection to pontine nuclei subareas is relayed to the highly divergent pontocerebellar projection terminating in overlapping specific lobules of the cerebellum. Consequently, the mode of the pontine nuclei relay underlies the cerebellar functional organization.

The ventral striatum contributes to the activity of the motor cortex and motor outputs in monkeys

The ventral striatum (VSt) is thought to be involved in the vigor of motivated behavior and is suggested to be a limbic-motor interface between limbic areas involved in motivational processes and neural circuits regulating behavioral outputs. However, there is little direct evidence demonstrating the involvement of the VSt in motor control for motivated behaviors. To clarify the functional role of the VSt in motor control, we investigated the effect of reversible pharmacological inactivation of the VSt on the oscillatory activity of the sensorimotor cortices and motor outputs in two macaque monkeys. VSt inactivation reduced movement-related activities of the primary motor cortex and premotor area at 15–120 Hz and increased those at 5–7 Hz. These changes were accompanied by reduced torque outputs but had no effect on the correct performance rate. The present study provides direct evidence that the VSt regulates activities of the motor cortices and motor output.

Origin of Multisynaptic Corticospinal Pathway to Forelimb Segments in Macaques and Its Reorganization After Spinal Cord Injury

Removal of the monosynaptic corticospinal pathway (CSP) terminating within the forelimb segments severely impairs manual dexterity. Functional recovery from the monosynaptic CSP lesion can be achieved through the remaining multisynaptic CSP toward the forelimb segments. In the present study, we applied retrograde transsynaptic labeling with rabies virus to a monkey model of spinal cord injury. By injecting the virus into the spinal forelimb segments immediately after the monosynaptic CSP lesion, we showed that the contralateral primary motor cortex (M1), especially its caudal and bank region (so-called “new” M1), was the principal origin of the CSP linking the motor cortex to the spinal forelimb segments disynaptically (disynaptic CSP). This forms a striking contrast to the architecture of the monosynaptic CSP that involves extensively other motor-related areas, together with M1. Next, the rabies injections were made at the recovery period of 3 months after the monosynaptic CSP lesion. The second-order labeled neurons were located in the ipsilateral as well as in the contralateral “new” M1. This indicates that the disynaptic CSP input from the ipsilateral “new” M1 is recruited during the motor recovery from the monosynaptic CSP lesion. Our results suggest that the disynaptic CSP is reorganized to connect the ipsilateral “new” M1 to the forelimb motoneurons for functional compensation after the monosynaptic CSP lesion.

A multisynaptic pathway from the ventral midbrain toward spinal motoneurons in monkeys

Abstract

Motivation boosts motor performance. Activity of the ventral midbrain (VM), consisting of the ventral tegmental area (VTA), the substantia nigra pars compacta (SNc) and the retrorubral field (RRF), plays an important role in processing motivation. However, little is known about the neural substrate bridging the VM and the spinal motor output. We hypothesized that the VM might exert a modulatory influence over the descending motor pathways. By retrograde transneuronal labelling with rabies virus, we demonstrated the existence of multisynaptic projections from the VM to the cervical enlargement in monkeys. The distribution pattern of spinal projection neurons in the VM exhibited a caudorostral gradient, in that the RRF and the caudal part of the SNc contained more retrogradely labelled neurons than the VTA and the rostral part of the SNc. Electrical stimulation of the VM induced muscle responses in the contralateral forelimb with a delay of a few milliseconds following the responses of the ipsilateral primary motor cortex (M1). The magnitude and number of evoked muscle responses were associated with the stimulus intensity and number of pulses. The muscle responses were diminished during M1 inactivation. Thus, the present study has identified a multisynaptic VM–spinal pathway that is mediated, at least in part, by the M1 and might play a pivotal role in modulatory control of the spinal motor output.

Key points

Motivation to obtain reward is thought to boost motor performance, and activity in the ventral midbrain is important to the motivational process.

Little is known about a neural substrate bridging the ventral midbrain and the spinal motor output.

Retrograde trans‐synaptic experiments revealed that the ventral midbrain projects multisynaptically to the spinal cord in macaque monkeys.

Ventral midbrain activation by electrical stimulation generated cortical activity in the motor cortex and forelimb muscle activity.

A multisynaptic ventral midbrain–spinal pathway most probably plays a pivotal role in modulatory control of the spinal motor output.

Cortico-Cerebellar Hyper-Connections and Reduced Purkinje Cells Behind Abnormal Eyeblink Conditioning in a Computational Model of Autism Spectrum Disorder

Empirical evidence suggests that children with autism spectrum disorder (ASD) show abnormal behavior during delay eyeblink conditioning. They show a higher conditioned response learning rate and earlier peak latency of the conditioned response signal. The neuronal mechanisms underlying this autistic behavioral phenotype are still unclear. Here, we use a physiologically constrained spiking neuron model of the cerebellar-cortical system to investigate which features are critical to explaining atypical learning in ASD. Significantly, the computer simulations run with the model suggest that the higher conditioned responses learning rate mainly depends on the reduced number of Purkinje cells. In contrast, the earlier peak latency mainly depends on the hyper-connections of the cerebellum with sensory and motor cortex. Notably, the model has been validated by reproducing the behavioral data collected from studies with real children. Overall, this article is a starting point to understanding the link between the behavioral and neurobiological basis in ASD learning. At the end of the paper, we discuss how this knowledge could be critical for devising new treatments.

Role of the nucleus accumbens in functional recovery from spinal cord injury

Post brain damage depression impedes functional recovery. On the other hand, higher motivation facilitates functional recovery after damage to the central nervous system, but the neural mechanism of psychological effects on functional recovery is unclear. The nucleus accumbens (NAcc), a motivation center, has not been considered directly involved in motor function. Recently, it was demonstrated that the NAcc makes a direct contribution to motor performance after spinal cord injury by facilitating motor cortex activity. In this perspective, we first summarize our investigation of role of NAcc in motor control during the recovery course after spinal cord injury, followed by a discussion of the current knowledge regarding the relationship between the recovery and NAcc after neuronal damage.

The Role of the Medial Prefrontal Cortex in Moderating Neural Representations of Self and Other in Primates

As a frontal node in the primate social brain, the medial prefrontal cortex (MPFC) plays a critical role in coordinating one's own behavior with respect to that of others. Current literature demonstrates that single neurons in the MPFC encode behavior-related variables such as intentions, actions, and rewards, specifically for self and other, and that the MPFC comes into play when reflecting upon oneself and others. The social moderator account of MPFC function can explain maladaptive social cognition in people with autism spectrum disorder, which tips the balance in favor of self-centered perspectives rather than taking into consideration the perspective of others. Several strands of evidence suggest a hypothesis that the MPFC represents different other mental models, depending on the context at hand, to better predict others' emotions and behaviors. This hypothesis also accounts for aberrant MPFC activity in autistic individuals while they are mentalizing others.

Morphological features of large layer V pyramidal neurons in cortical motor-related areas of macaque monkeys: analysis of basal dendrites

In primates, large layer V pyramidal neurons located in the frontal motor-related areas send a variety of motor commands to the spinal cord, giving rise to the corticospinal tract, for execution of skilled motor behavior. However, little is known about the morphological diversity of such pyramidal neurons among the areas. Here we show that the structure of basal dendrites of the large layer V pyramidal neurons in the dorsal premotor cortex (PMd) is different from those in the other areas, including the primary motor cortex, the supplementary motor area, and the ventral premotor cortex. In the PMd, not only the complexity (arborization) of basal dendrites, i.e., total dendritic length and branching number, was poorly developed, but also the density of dendritic spines was so low, as compared to the other motor-related areas. Regarding the distribution of the three dendritic spine types identified, we found that thin-type (more immature) spines were prominent in the PMd in comparison with stubby- and mushroom-type (more mature) spines, while both thin- and stubby-type spines were in the other areas. The differential morphological features of basal dendrites might reflect distinct patterns of motor information processing within the large layer V pyramidal neurons in individual motor-related areas.

Socially relative reward valuation in the primate brain

Reward valuation in social contexts is by nature relative rather than absolute; it is made in reference to others. This socially relative reward valuation is based on our propensity to conduct comparisons and competitions between self and other. Exploring its neural substrate has been an active area of research in human neuroimaging. More recently, electrophysiological investigation of the macaque brain has enabled us to understand neural mechanisms underlying this valuation process at single-neuron and network levels. Here I show that shared neural networks centered at the medial prefrontal cortex and dopamine-related subcortical regions are involved in this process in humans and nonhuman primates. Thus, socially relative reward valuation is mediated by cortico-subcortically coordinated activity linking social and reward brain networks.

How the Cerebellum and Prefrontal Cortex Cooperate During Trace Eyeblinking Conditioning

Several data have demonstrated that during the widely used experimental paradigm for studying associative learning, trace eye blinking conditioning (TEBC), there is a strong interaction between cerebellum and medial prefrontal cortex (mPFC). Despite this evidence, the neural mechanisms underlying this interaction are still not clear. Here, we propose a neurophysiologically plausible computational model to address this issue. The model is constrained on the basis of two critical anatomo-physiological features: (i) the cerebello-cortical organization through two circuits, respectively, targeting M1 and mPFC; (ii) the different timing in the plasticity mechanisms of these parallel circuits produced by the granule cells time sensitivity according to which different subpopulations are active at different moments during conditioned stimuli. The computer simulations run with the model suggest that these features are critical to understand how the cooperation between cerebellum and mPFC supports motor areas during TEBC. In particular, a greater trace interval produces greater plasticity changes at the slow path synapses involving mPFC with respect to plasticity changes at the fast path involving M1. As a consequence, the greater is the trace interval, the stronger is the mPFC involvement. The model has been validated by reproducing data collected through recent real mice experiments.

Representation of distinct reward variables for self and other in primate lateral hypothalamus

Motivation is affected by rewards to both oneself and others. Which brain regions separately monitor self-rewards and other-rewards? It has been thought that higher-order, neocortical regions, such as the medial prefrontal cortex, monitor behavioral information in agent-selective manners. Here, we show that a subcortical region called the lateral hypothalamus (LH), an evolutionarily old structure in the vertebrate brain, also contains agent-specific reward information and further integrates it into a subjective reward value. This other-reward–dependent value signal is causally used for adaptive behavior, because deactivation of LH cells totally eliminates the motivational impact of other-rewards. Our findings indicate that the LH is an integral component of social brain networks and shapes socially motivated behavior via functional coordination with neocortical regions.

The lateral hypothalamus (LH) has long been implicated in maintaining behavioral homeostasis essential for the survival of an individual. However, recent evidence suggests its more widespread roles in behavioral coordination, extending to the social domain. The neuronal and circuit mechanisms behind the LH processing of social information are unknown. Here, we show that the LH represents distinct reward variables for “self” and “other” and is causally involved in shaping socially motivated behavior. During a Pavlovian conditioning procedure incorporating ubiquitous social experiences where rewards to others affect one’s motivation, LH cells encoded the subjective value of self-rewards, as well as the likelihood of self- or other-rewards. The other-reward coding was not a general consequence of other’s existence, but a specific effect of other’s reward availability. Coherent activity with and top-down information flow from the medial prefrontal cortex, a hub of social brain networks, contributed to signal encoding in the LH. Furthermore, deactivation of LH cells eliminated the motivational impact of other-rewards. These results indicate that the LH constitutes a subcortical node in social brain networks and shapes one’s motivation by integrating cortically derived, agent-specific reward information.

The Ventral Striatum is a Key Node for Functional Recovery of Finger Dexterity After Spinal Cord Injury in Monkeys

In a recent study, we demonstrated that the ventral striatum (VSt) controls finger movements directly during the early recovery stage after spinal cord injury (SCI), implying that the VSt may be a part of neural substrates responsible for the recovery of dexterous finger movements. The VSt is accepted widely as a key node for motivation, but is not thought to be involved in the direct control of limb movements. Therefore, whether a causal relationship exists between the VSt and motor recovery after SCI is unknown, and the role of the VSt in the recovery of dexterous finger movements orfinger movements in general after SCI remains unclear. In the present study, functional brain imaging in a macaque model of SCI revealed a strengthened functional connectivity between motor-related areas and the VSt during the recovery process for precision grip, but not whole finger grip after SCI. Furthermore, permanent lesion of the VSt impeded the recoveryof precision grip, but not coarse grip. Thus, the VSt was needed specifically for functional recovery of dexterous finger movements. These results suggest that the VSt is the key node of the cortical reorganization required for functional recovery of finger dexterity.

Dexterous Hand Movements and Their Recovery After Central Nervous System Injury

Hand dexterity has uniquely developed in higher primates and is thought to rely on the direct corticomotoneuronal (CM) pathway. Recent studies have shown that rodents and carnivores lack the direct CM pathway but can control certain levels of dexterous hand movements through various indirect CM pathways. Some homologous pathways also exist in higher primates, and among them, propriospinal (PrS) neurons in the mid-cervical segments (C3-C4) are significantly involved in hand dexterity. When the direct CM pathway was lesioned caudal to the PrS and transmission of cortical commands to hand motoneurons via the PrS neurons remained intact, dexterous hand movements could be significantly recovered. This recovery model was intensively studied, and it was found that, in addition to the compensation by the PrS neurons, a large-scale reorganization in the bilateral cortical motor-related areas and mesolimbic structures contributed to recovery. Future therapeutic strategies should target these multihierarchical areas.

Disentangling motor planning and motor execution in unmedicated de novo Parkinson's disease patients: An fMRI study

Many studies have used functional magnetic resonance imaging to unravel the neuronal underpinnings of motor system abnormalities in Parkinson's disease, indicating functional inhibition at the level of basal ganglia-thalamo-cortical motor networks. The study aim was to extend the characterization of functional motor changes in Parkinson's Disease by dissociating between two phases of action (i.e. motor planning and motor execution) during an automated unilateral finger movement sequence with the left and right hand, separately. In essence, we wished to identify neuronal dysfunction and potential neuronal compensation before (planning) and during (execution) automated sequential motor behavior in unmedicated early stage Parkinson's Disease patients. Twenty-two Parkinson's Disease patients (14 males; 53 ± 11 years; Hoehn and Yahr score 1.4 ± 0.6; UPDRS (part 3) motor score 16 ± 6) and 22 healthy controls (14 males; 49 ± 12 years) performed a pre-learnt four finger sequence (index, ring, middle and little finger, in order), either self-initiated (FREE) or externally triggered (REACT), within an 8-second time window. Findings were most pronounced during FREE with the clinically most affected side, where motor execution revealed significant underactivity of contralateral primary motor cortex, contralateral posterior putamen (sensorimotor territory), ipsilateral anterior cerebellum / cerebellar vermis, along with underactivity in supplementary motor area (based on ROI analyses only), corroborating previous findings in Parkinson's Disease. During motor planning, Parkinson's Disease patients showed a significant relative overactivity in dorsolateral prefrontal cortex (DLPFC), suggesting a compensatory overactivity. To a variable extent this relative overactivity in the DLPFC went along with a relative overactivity in the precuneus and the ipsilateral anterior cerebellum/cerebellar vermis Our study illustrates that a refined view of disturbances in motor function and compensatory processes can be gained from experimental designs that try to dissociate motor planning from motor execution, emphasizing that compensatory mechanisms are triggered in Parkinson's Disease when voluntary movements are conceptualized for action.

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Dissociated activations in early stage PD for motor planning and motor execution

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PD patients show frontal-parietal network compensation during self-initiated movement.

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Compensation for an impaired basal ganglia-premotor circuit occurs during planning.

Fear conditioning and extinction induce opposing changes in dendritic spine remodeling and somatic activity of layer 5 pyramidal neurons in the mouse motor cortex

Multiple brain regions including the amygdala and prefrontal cortex are crucial for modulating fear conditioning and extinction. The primary motor cortex is known to participate in the planning, control, and execution of voluntary movements. Whether and how the primary motor cortex is involved in modulating freezing responses related to fear conditioning and extinction remains unclear. Here we show that inactivation of the mouse primary motor cortex impairs both the acquisition and extinction of freezing responses induced by auditory-cued fear conditioning. Fear conditioning significantly increases the elimination of dendritic spines on apical dendrites of layer 5 pyramidal neurons in the motor cortex. These eliminated spines are further apart from each other than expected from random distribution along dendrites. On the other hand, fear extinction causes the formation of new spines that are located near the site of spines eliminated previously after fear conditioning. We further show that fear conditioning decreases and fear extinction increases somatic activities of layer 5 pyramidal neurons in the motor cortex respectively. Taken together, these findings indicate fear conditioning and extinction induce opposing changes in synaptic connections and somatic activities of layer 5 pyramidal neurons in the primary motor cortex, a cortical region important for the acquisition and extinction of auditory-cued conditioned freezing responses.

Network connectivity of motor control in the ageing brain

Older individuals typically display stronger regional brain activity than younger subjects during motor performance. However, knowledge regarding age-related changes of motor network interactions between brain regions remains scarce. We here investigated the impact of ageing on the interaction of cortical areas during movement selection and initiation using dynamic causal modelling (DCM). We found that age-related psychomotor slowing was accompanied by increases in both regional activity and effective connectivity, especially for ‘core’ motor coupling targeting primary motor cortex (M1). Interestingly, younger participants within the older group showed strongest connectivity targeting M1, which steadily decreased with advancing age. Conversely, prefrontal influences on the motor system increased with advancing age, and were inversely correlated with reduced parietal influences and core motor coupling. Interestingly, higher net coupling within the prefrontal-premotor-M1 axis predicted faster psychomotor speed in ageing. Hence, as opposed to a uniform age-related decline, our findings are compatible with the idea of different age-related compensatory mechanisms, with an important role of the prefrontal cortex compensating for reduced coupling within the core motor network.

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Enhanced motor network activity and connectivity in ageing

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Parietal-premotor and premotor-M1 coupling decreases with advancing age.

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Prefrontal influences on the motor system increase with advancing age.

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Prefrontal cortex compensates for age-related decline in other motor connections.

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Prefrontal-premotor-M1 coupling predicts psychomotor speed in ageing.

The Brain Is Needed to Cure Spinal Cord Injury

Damage to corticospinal fibers in the cervical spinal cord is known to impair dexterous hand movements. However, accumulating evidence has shown that precision grip can recover considerably through rehabilitative training. Recent multidisciplinary studies have revealed that, at the spinal level, this recovery is possible due to an indirect neural pathway through propriospinal neurons (PNs), which relay cortical commands to hand motoneurons. Although this indirect spinal pathway is heavily involved in recovery, its role is dwarfed by a simultaneous large-scale network reorganization spanning motor-related cortices and mesolimbic structures. This large-scale network reorganization is key to the regulation of recovery and future therapeutic strategies will need to take into account the involvement of these supraspinal centers in addition to the known role of the spinal cord.

Operant conditioning of neural activity in freely behaving monkeys with intracranial reinforcement

Operant conditioning of neural activity has typically been performed under controlled behavioral conditions using food reinforcement. This has limited the duration and behavioral context for neural conditioning. To reward cell activity in unconstrained primates, we sought sites in nucleus accumbens (NAc) whose stimulation reinforced operant responding. In three monkeys, NAc stimulation sustained performance of a manual target-tracking task, with response rates that increased monotonically with increasing NAc stimulation. We recorded activity of single motor cortex neurons and documented their modulation with wrist force. We conditioned increased firing rates with the monkey seated in the training booth and during free behavior in the cage using an autonomous head-fixed recording and stimulating system. Spikes occurring above baseline rates triggered single or multiple electrical pulses to the reinforcement site. Such rate-contingent, unit-triggered stimulation was made available for periods of 1-3 min separated by 3-10 min time-out periods. Feedback was presented as event-triggered clicks both in-cage and in-booth, and visual cues were provided in many in-booth sessions. In-booth conditioning produced increases in single neuron firing probability with intracranial reinforcement in 48 of 58 cells. Reinforced cell activity could rise more than five times that of non-reinforced activity. In-cage conditioning produced significant increases in 21 of 33 sessions. In-cage rate changes peaked later and lasted longer than in-booth changes, but were often comparatively smaller, between 13 and 18% above non-reinforced activity. Thus intracranial stimulation reinforced volitional increases in cortical firing rates during both free behavior and a controlled environment, although changes in the latter were more robust.NEW & NOTEWORTHY Closed-loop brain-computer interfaces (BCI) were used to operantly condition increases in muscle and neural activity in monkeys by delivering activity-dependent stimuli to an intracranial reinforcement site (nucleus accumbens). We conditioned increased firing rates with the monkeys seated in a training booth and also, for the first time, during free behavior in a cage using an autonomous head-fixed BCI.

Neural Activity during Voluntary Movements in Each Body Representation of the Intracortical Microstimulation-Derived Map in the Macaque Motor Cortex

In order to accurately interpret experimental data using the topographic body map identified by conventional intracortical microstimulation (ICMS), it is important to know how neurons in each division of the map respond during voluntary movements. Here we systematically investigated neuronal responses in each body representation of the ICMS map during a reach-grasp-retrieval task that involves the movements of multiple body parts. The topographic body map in the primary motor cortex (M1) generally corresponds to functional divisions of voluntary movements; neurons at the recording sites in each body representation with movement thresholds of 10 μA or less were differentially activated during the task, and the timing of responses was consistent with the movements of the body part represented. Moreover, neurons in the digit representation responded differently for the different types of grasping. In addition, the present study showed that neural activity depends on the ICMS current threshold required to elicit body movements and the location of the recording on the cortical surface. In the ventral premotor cortex (PMv), no correlation was found between the response properties of neurons and the body representation in the ICMS map. Neural responses specific to forelimb movements were often observed in the rostral part of PMv, including the lateral bank of the lower arcuate limb, in which ICMS up to 100 μA evoked no detectable movement. These results indicate that the physiological significance of the ICMS-derived maps is different between, and even within, areas M1 and PMv.

Rostrocaudal functional gradient among the pre-dorsal premotor cortex, dorsal premotor cortex and primary motor cortex in goal-directed motor behaviour

The dorsal premotor cortex residing in the dorsolateral aspect of area 6 is a rostrocaudally elongated area that is rostral to the primary motor cortex (M1) and caudal to the prefrontal cortex. This region, which is subdivided into rostral [pre-dorsal premotor cortex (pre-PMd)] and caudal [dorsal premotor cortex proper (PMd)] components, probably plays a central role in planning and executing actions to achieve a behavioural goal. In the present study, we investigated the functional specializations of the pre-PMd, PMd, and M1, because the synthesis of the specific functions performed by each area is considered to be essential. Neurons were recorded while monkeys performed a conditional visuo-goal task designed to include separate processes for determining a behavioural goal (reaching towards a right or left potential target) on the basis of visual object instructions, specifying actions (direction of reaching) to be performed on the basis of the goal, and preparing and executing the action. Neurons in the pre-PMd and PMd retrieved and maintained behavioural goals without encoding the visual features of the visual object instructions, and subsequently specified the actions by multiplexing the goals with the locations of the targets. Furthermore, PMd and M1 neurons played a major role in representing the action during movement preparation and execution, whereas the contribution of the pre-PMd progressively decreased as the time of the actual execution of the movement approached. These findings revealed that the multiple processing stages necessary for the realization of an action to accomplish a goal were implemented in an area-specific manner across a functional gradient from the pre-PMd to M1 that included the PMd as an intermediary.

A Prefrontal-Hippocampal Comparator for Goal-Directed Behavior: The Intentional Self and Episodic Memory

The hypothesis of this article is that the interactions between the prefrontal cortex and the hippocampus play a critical role in the modulation of goal-directed self-action and the strengthening of episodic memories. We describe various theories that model a comparator function for the hippocampus, and then elaborate the empirical evidence that supports these theories. One theory which describes a prefrontal-hippocampal comparator for voluntary action is emphasized. Action plans are essential for successful goal-directed behavior, and are elaborated by the prefrontal cortex. When an action plan is initiated, the prefrontal cortex transmits an efference copy (or corollary discharge) to the hippocampus where it is stored as a working memory for the action plan (which includes the expected outcomes of the action plan). The hippocampus then serves as a response intention-response outcome working memory comparator. Hippocampal comparator function is enabled by the hippocampal theta rhythm allowing the hippocampus to compare expected action outcomes to actual action outcomes. If the expected and actual outcomes match, the hippocampus transmits a signal to prefrontal cortex which strengthens or consolidates the action plan. If a mismatch occurs, the hippocampus transmits an error signal to the prefrontal cortex which facilitates a reformulation of the action plan, fostering behavioral flexibility and memory updating. The corollary discharge provides the self-referential component to the episodic memory, affording the personal and subjective experience of what behavior was carried out, when it was carried out, and in what context (where) it occurred. Such a perspective can be applied to episodic memory in humans, and episodic-like memory in non-human animal species.

Function of the nucleus accumbens in motor control during recovery after spinal cord injury

Motivation facilitates recovery after neuronal damage, but its mechanism is elusive. It is generally thought that the nucleus accumbens (NAc) regulates motivation-driven effort but is not involved in the direct control of movement. Using causality analysis, we identified the flow of activity from the NAc to the sensorimotor cortex (SMC) during the recovery of dexterous finger movements after spinal cord injury at the cervical level in macaque monkeys. Furthermore, reversible pharmacological inactivation of the NAc during the early recovery period diminished high-frequency oscillatory activity in the SMC, which was accompanied by a transient deficit of amelioration in finger dexterity obtained by rehabilitation. These results demonstrate that during recovery after spinal damage, the NAc up-regulates the high-frequency activity of the SMC and is directly involved in the control of finger movements.

Plasticity for recovery after partial spinal cord injury – hierarchical organization

To cure the impaired physiological functions after the spinal cord injury, not only development of molecular therapies for axonal regeneration, but also that of therapeutic strategies to induce appropriate rewiring of neural circuits should be necessary. For this purpose, understanding the plastic changes in the central nervous system during spontaneous recovery following the injury would be helpful. In this article, a series of studies conducted in the authors’ laboratory on the reorganization of neural networks in the partial spinal cord injury model using macaque monkeys are reviewed. In this model, after selective lesion of the lateral corticospinal tract at the fifth cervical segment, dexterous digit movements are once impaired, but recover through rehabilitative training in a few weeks to a few months. During the recovery, synaptic transmission and organization of the neural circuits exhibit drastic changes depending on the time after the injury, not only in the spinal cord, but also in hierarchically higher order structures such as motor-related cortical areas and even in limbic structures. It is suggested that on top of the molecular therapies, neurorehabilitative and neuromodulatory therapies targeting such higher order structures should be helpful in inducing appropriate rewiring of the neural circuits.

Rule Activity Related to Spatial and Numerical Magnitudes: Comparison of Prefrontal, Premotor, and Cingulate Motor Cortices

In everyday situations, quantitative rules, such as “greater than/less than,” need to be applied to a multitude of magnitude comparisons, be they sensory, spatial, temporal, or numerical. We have previously shown that rules applied to different magnitudes are encoded in the lateral PFC. To investigate if and how other frontal lobe areas also contribute to the encoding of quantitative rules applied to multiple magnitudes, we trained monkeys to switch between “greater than/less than” rules applied to either line lengths (spatial magnitudes) or dot numerosities (discrete numerical magnitudes). We recorded single-cell activity from the dorsal premotor cortex (dPMC) and cingulate motor cortex (CMA) and compared it with PFC activity. We found the largest proportion of quantitative rule-selective cells in PFC (24% of randomly selected cells), whereas neurons in dPMC and CMA rarely encoded the rule (6% of the cells). In addition, rule selectivity of individual cells was highest in PFC neurons compared with dPMC and CMA neurons. Rule-selective neurons that simultaneously represented the “greater than/less than” rules applied to line lengths and numerosities (“rule generalists”) were exclusively present in PFC. In dPMC and CMA, however, neurons primarily encoded rules applied to only one of the two magnitude types (“rule specialists”). Our data suggest a special involvement of PFC in representing quantitative rules at an abstract level, both in terms of the proportion of neurons engaged and the coding capacities.

The organization of dorsal frontal cortex in humans and macaques

The human dorsal frontal cortex has been associated with the most sophisticated aspects of cognition, including those that are thought to be especially refined in humans. Here we used diffusion-weighted magnetic resonance imaging (DW-MRI) and functional MRI (fMRI) in humans and macaques to infer and compare the organization of dorsal frontal cortex in the two species. Using DW-MRI tractography-based parcellation, we identified 10 dorsal frontal regions lying between the human inferior frontal sulcus and cingulate cortex. Patterns of functional coupling between each area and the rest of the brain were then estimated with fMRI and compared with functional coupling patterns in macaques. Areas in human medial frontal cortex, including areas associated with high-level social cognitive processes such as theory of mind, showed a surprising degree of similarity in their functional coupling patterns with the frontal pole, medial prefrontal, and dorsal prefrontal convexity in the macaque. We failed to find evidence for "new" regions in human medial frontal cortex. On the lateral surface, comparison of functional coupling patterns suggested correspondences in anatomical organization distinct from those that are widely assumed. A human region sometimes referred to as lateral frontal pole more closely resembled area 46, rather than the frontal pole, of the macaque. Overall the pattern of results suggest important similarities in frontal cortex organization in humans and other primates, even in the case of regions thought to carry out uniquely human functions. The patterns of interspecies correspondences are not, however, always those that are widely assumed.

Multisynaptic projections from the ventrolateral prefrontal cortex to hand and mouth representations of the monkey primary motor cortex

Different sectors of the prefrontal cortex have distinct neuronal connections with higher-order sensory areas and/or limbic structures and are related to diverse aspects of cognitive functions, such as visual working memory and reward-based decision-making. Recent studies have revealed that the prefrontal cortex (PF), especially the lateral PF, is also involved in motor control. Hence, different sectors of the PF may contribute to motor behaviors with distinct body parts. To test this hypothesis anatomically, we examined the patterns of multisynaptic projections from the PF to regions of the primary motor cortex (MI) that represent the arm, hand, and mouth, using retrograde transsynaptic transport of rabies virus. Four days after rabies injections into the hand or mouth region, particularly dense neuron labeling was observed in the ventrolateral PF, including the convexity part of ventral area 46. After the rabies injections into the mouth region, another dense cluster of labeled neurons was seen in the orbitofrontal cortex (area 13). By contrast, rabies labeling of PF neurons was rather sparse in the arm-injection cases. The present results suggest that the PF-MI multisynaptic projections may be organized such that the MI hand and mouth regions preferentially receive cognitive information for execution of elaborate motor actions.

Brain activity during motor imagery of an action with an object: a functional magnetic resonance imaging study

We utilized functional magnetic resonance imaging to investigate the brain regions activated during motor imagery of an action with an object both with and without passively holding the object. Participants performed the following tasks: (1) 'Imagery with Ball' condition: subjects imagined squeezing a foam ball (7cm diameter) while holding the ball, (2) 'Imagery' condition: subjects imagined squeezing a ball without holding the ball, and (3) 'Ball' condition: subjects held the ball without motor imagery. Regions activated by the 'Imagery with Ball' condition were located in the left dorsolateral prefrontal cortex (DLPFC), supplemental motor areas (SMA), inferior parietal lobule (IPL), superior parietal lobule (SPL), insula, cerebellum and basal ganglia. A direct comparison revealed that the right DLPFC and the right IPL showed a higher level of activation during the 'Imagery with Ball' than during the 'Imagery'+'Ball' conditions. Our studies suggested that the right front-parietal networks were involved in the motor imagery of an action with an object.

Guanfacine modulates the influence of emotional cues on prefrontal cortex activation for cognitive control

RATIONALE

Functional interactions between limbic regions that process emotions and frontal networks that guide response functions provide a substrate for emotional cues to influence behavior. Stimulation of postsynaptic α₂ adrenoceptors enhances the function of prefrontal regions in these networks. However, the impact of this stimulation on the emotional biasing of behavior has not been established.

OBJECTIVES

This study tested the effect of the postsynaptic α₂ adrenoceptor agonist guanfacine on the emotional biasing of response execution and inhibition in prefrontal cortex.

METHODS

Fifteen healthy young adults were scanned twice with functional magnetic resonance imaging while performing a face emotion go/no-go task following counterbalanced administration of single doses of oral guanfacine (1 mg) and placebo in a double-blind, cross-over design.

RESULTS

Lower perceptual sensitivity and less response bias for sad faces resulted in fewer correct responses compared to happy and neutral faces but had no effect on correct inhibitions. Guanfacine increased the sensitivity and bias selectively for sad faces, resulting in response accuracy comparable to happy and neutral faces, and reversed the valence-dependent variation in response-related activation in left dorsolateral prefrontal cortex (DLPFC), resulting in enhanced activation for response execution cued by sad faces relative to happy and neutral faces, in line with other frontoparietal regions.

CONCLUSIONS

These results provide evidence that guanfacine stimulation of postsynaptic α₂ adrenoceptors moderates DLPFC activation associated with the emotional biasing of response execution processes. The findings have implications for the α₂ adrenoceptor agonist treatment of attention-deficit hyperactivity disorder.

Category representation and generalization in the prefrontal cortex

Categorization is a function of the brain that serves to group together items and events in our environments. Here we review the following important issues related to category representation and generalization: namely, where categories are presented in the brain, and how the brain utilizes categorical membership to generate new information. Accumulated experimental evidence shows that the prefrontal cortex (PFC) plays a critical role in category formation and generalization. We propose that prefrontal neurons abstract the commonality beyond individual stimuli, and categorize these based on their common meaning by ignoring their physical properties and learning to represent the boundaries between behaviorally significant categories. We also claim that a subgroup of prefrontal neurons simultaneously receives the category-related information and specific property information (e.g. reward) associated with an exemplar, to form a category-based representation of that property, and propagates it among stimuli of the same category, possibly reflecting a neural basis for category generalization in the PFC. These results suggest that the PFC is involved in representing abstract rules, and generating new information on the basis of previously acquired knowledge.

Transneuronal tracing with neurotropic viruses reveals network macroarchitecture

A major challenge in systems neuroscience is to unravel the complex matrix of connections that characterize functional circuits within the central nervous system. Retrograde transneuronal transport of rabies virus has proven to be especially useful for this purpose. Here we provide specific examples in which transneuronal transport of rabies virus has been used to unravel multi-synaptic pathways within motor, cognitive and autonomic circuits. Tracing with rabies virus defined: first, the closed-loop organization of cerebellar and basal ganglia circuits with the cerebral cortex; second, the presence of bidirectional communication between the cerebellum and basal ganglia; third, the specific cortical areas that have monosynaptic and/or disynaptic connections to spinal motoneurons in non-human primates; and fourth, the areas in the cerebral cortex with the most direct influence on the sympathetic innervation of the kidney. These examples demonstrate the power of transneuronal tracing with rabies virus to identify the macroarchitecture of complex neural circuits.

Multisynaptic inputs from the medial temporal lobe to V4 in macaques

Retrograde transsynaptic transport of rabies virus was employed to undertake the top-down projections from the medial temporal lobe (MTL) to visual area V4 of the occipitotemporal visual pathway in Japanese monkeys (Macaca fuscata). On day 3 after rabies injections into V4, neuronal labeling was observed prominently in the temporal lobe areas that have direct connections with V4, including area TF of the parahippocampal cortex. Furthermore, conspicuous neuron labeling appeared disynaptically in area TH of the parahippocampal cortex, and areas 35 and 36 of the perirhinal cortex. The labeled neurons were located predominantly in deep layers. On day 4 after the rabies injections, labeled neurons were found in the hippocampal formation, along with massive labeling in the parahippocampal and perirhinal cortices. In the hippocampal formation, the densest neuron labeling was seen in layer 5 of the entorhinal cortex, and a small but certain number of neurons were labeled in other regions, such as the subicular complex and CA1 and CA3 of the hippocampus proper. The present results indicate that V4 receives major input from the hippocampus proper via the entorhinal cortex, as well as “short-cut” pathways that bypass the entorhinal cortex. These multisynaptic pathways may define an anatomical basis for hippocampal-cortical interactions involving lower visual areas. The multisynaptic input from the MTL to V4 is likely to provide mnemonic information about object recognition that is accomplished through the occipitotemporal pathway.

Dynamic modulation of intrinsic functional connectivity by transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique capable of modulating cortical excitability and thereby influencing behavior and learning. Recent evidence suggests that bilateral tDCS over both primary sensorimotor cortices (SM1) yields more prominent effects on motor performance in both healthy subjects and chronic stroke patients than unilateral tDCS over SM1. To better characterize the underlying neural mechanisms of this effect, we aimed to explore changes in resting-state functional connectivity during both stimulation types. In a randomized single-blind crossover design, 12 healthy subjects underwent functional magnetic resonance imaging at rest before, during, and after 20 min of unilateral, bilateral, and sham tDCS stimulation over SM1. Eigenvector centrality mapping (ECM) was used to investigate tDCS-induced changes in functional connectivity patterns across the whole brain. Uni- and bilateral tDCS over SM1 resulted in functional connectivity changes in widespread brain areas compared with sham stimulation both during and after stimulation. Whereas bilateral tDCS predominantly modulated changes in primary and secondary motor as well as prefrontal regions, unilateral tDCS affected prefrontal, parietal, and cerebellar areas. No direct effect was seen under the stimulating electrode in the unilateral condition. The time course of changes in functional connectivity in the respective brain areas was nonlinear and temporally dispersed. These findings provide evidence toward a network-based understanding regarding the underpinnings of specific tDCS interventions.

Anatomical evidence for the involvement of medial cerebellar output from the interpositus nuclei in cognitive functions

Although the cerebellar interpositus nuclei are known to be involved in cognitive functions, such as associative motor learning, no anatomical evidence has been available for this issue. Here we used retrograde transneuronal transport of rabies virus to identify neurons in the cerebellar nuclei that project via the thalamus to area 46 of the prefrontal cortex of macaques in comparison with the projections to the primary motor cortex (M1). After rabies injections into area 46, many neurons in the restricted region of the posterior interpositus nucleus (PIN) were labeled disynaptically via the thalamus, whereas no neuron labeling was found in the anterior interpositus nucleus (AIN). The distribution of the labeled neurons was dorsoventrally different from that of PIN neurons labeled from the M1. This defines an anatomical substrate for the contribution of medial cerebellar output to cognitive functions. Like the dentate nucleus, the PIN has dual motor and cognitive channels, whereas the AIN has a motor channel only.

Dorsal area 46 is a major target of disynaptic projections from the medial temporal lobe

The medial temporal lobe (MTL) is responsible for various mnemonic functions, such as association/conjunction memory. The lateral prefrontal cortex (LPFC) also plays crucial roles in mnemonic functions and memory-based cognitive behaviors, for example, decision-making. Therefore, it is considered that the MTL and LPFC connect with each other and cooperate for the control of cognitive behaviors. However, there exist very weak, if any, direct inputs from the MTL to the LPFC. Employing retrograde transsynaptic transport of rabies virus, we investigated the organization of disynaptic bottom-up pathways connecting the MTL and the inferotemporal cortex to the LPFC in macaques. Three days after rabies injections into dorsal area 46, a large number of labeled neurons were observed in the MTL, such as the hippocampal formation (including the entorhinal cortex), the perirhinal cortex, and the parahippocampal cortex. In contrast, a majority of the labeled neurons were located in the inferotemporal cortex following rabies injections into ventral area 46 and lateral area 12. Rabies injections into lateral area 9/area 8B labeled only a small number of neurons in the MTL and the inferotemporal cortex. The present results indicate that, among the LPFC, dorsal area 46 is the main target of disynaptic inputs from the MTL.

Multisynaptic projections from the ventrolateral prefrontal cortex to the dorsal premotor cortex in macaques - anatomical substrate for conditional visuomotor behavior

Lines of evidence indicate that both the ventrolateral prefrontal cortex (vlPFC) (areas 45/12) and dorsal premotor cortex (PMd) (rostral F2 in area 6) are crucially involved in conditional visuomotor behavior, in which it is required to determine an action based on an associated visual object. However, virtually no direct projections appear to exist between the vlPFC and PMd. In the present study, to elucidate possible multisynaptic networks linking the vlPFC to the PMd, we performed a series of neuroanatomical tract-tracing experiments in macaque monkeys. First, we identified cortical areas that send projection fibers directly to the PMd by injecting Fast Blue into the PMd. Considerable retrograde labeling occurred in the dorsal prefrontal cortex (dPFC) (areas 46d/9/8B/8Ad), dorsomedial motor cortex (dmMC) (F7 and presupplementary motor area), rostral cingulate motor area, and ventral premotor cortex (F5 and area 44), whereas the vlPFC was virtually devoid of neuronal labeling. Second, we injected the rabies virus, a retrograde transneuronal tracer, into the PMd. At 3 days after the rabies injections, second-order neurons were labeled in the vlPFC (mainly area 45), indicating that the vlPFC disynaptically projects to the PMd. Finally, to determine areas that connect the vlPFC to the PMd indirectly, we carried out an anterograde/retrograde dual-labeling experiment in single monkeys. By examining the distribution of axon terminals labeled from the vlPFC and cell bodies labeled from the PMd, we found overlapping labels in the dPFC and dmMC. These results indicate that the vlPFC outflow is directed toward the PMd in a multisynaptic fashion through the dPFC and/or dmMC.

Segregated pathways carrying frontally derived top-down signals to visual areas MT and V4 in macaques

The bottom-up processing of visual information is strongly influenced by top-down signals, at least part of which is thought to be conveyed from the frontal cortex through the frontal eye field (FEF) and the lateral intraparietal area (LIP). Here we investigated the architecture of multisynaptic pathways from the frontal cortex to the middle temporal area (MT) of the dorsal visual stream and visual area 4 (V4) of the ventral visual stream in macaques. In the first series of experiments, the retrograde trans-synaptic tracer, rabies virus, was injected into MT or V4. Three days after rabies injections, the second-order (disynaptically connected) neuron labeling appeared in the ventral part of area 46 (area 46v), along with the first-order (monosynaptically connected) neuron labeling in FEF and LIP. In the MT-injection case, second-order neurons were also observed in the supplementary eye field (SEF). In the next series of experiments, double injections of two fluorescent dyes, fast blue and diamidino yellow, were made into MT and V4 to examine whether the frontal inputs are mediated by distinct or common neuronal populations. Virtually no double-labeled neurons were observed in FEF or LIP, indicating that separate neuronal populations mediate the frontal inputs to MT and V4. The present results define that the multisynaptic frontal input to V4 arises primarily from area 46v, whereas the input to MT arises from not only area 46v but also SEF, through distinct FEF and LIP neurons. Segregated pathways from the frontal cortex possibly carry the functionally diverse top-down signals to each visual stream.

Role of the prefrontal cortex in the cognitive control of reaching movements: near-infrared spectroscopy study

To elucidate the role of the prefrontal cortex in cognitive control of reaching movements, by multichannel near-infrared spectroscopy we examine changes in oxygenated hemoglobin (oxy-Hb) as an indicator of changes in regional cerebral blood flow in the bilateral dorsolateral (DLPFC), ventrolateral prefrontal cortex (VLPFC), and frontopolar cortex (FPC) during a reaching task with normal visual feedback (a consistent task) and a reaching task with flipped horizontal visual feedback (an inconsistent task). Subjects first perform 12 trials of the consistent task, and then perform six blocks of the inconsistent task, each of which consists of six trials. During the consistent task, oxy-Hb is increased only in the right VLPFC. During the first block of the inconsistent task, increases in oxy-Hb are observed in the bilateral DLPFC and the right VLPFC, whereas the increased oxy-Hb was gradually reduced as the block proceeded, which was accompanied by an improvement in the task performance. Eventually, there were no differences in the degree of change in oxy-Hb between the consistent and inconsistent tasks in the DLPFC and VLPFC. These findings suggest that the DLPFC is engaged in higher order cognitive control, while the right VLPFC is engaged in both higher and lower order cognitive controls.

Rabies virus as a transneuronal tracer of neuronal connections

Powerful transneuronal tracing technologies exploit the ability of some neurotropic viruses to travel across neuronal pathways and to function as self-amplifying markers. Rabies virus is the only viral tracer that is entirely specific, as it propagates exclusively between connected neurons by strictly unidirectional (retrograde) transneuronal transfer, allowing for the stepwise identification of neuronal connections of progressively higher order. Transneuronal tracing studies in primates and rodent models prior to the development of clinical disease have provided valuable information on rabies pathogenesis. We have shown that rabies virus propagation occurs at chemical synapses but not via gap junctions or cell-to-cell spread. Infected neurons remain viable, as they can express their neurotransmitters and cotransport other tracers. Axonal transport occurs at high speed, and all populations of the same synaptic order are infected simultaneously regardless of their neurotransmitters, synaptic strength, and distance, showing that rabies virus receptors are ubiquitously distributed within the CNS. Conversely, in the peripheral nervous system, rabies virus receptors are present only on motor endplates and motor axons, since uptake and transneuronal transmission to the CNS occur exclusively via the motor route, while sensory and autonomic endings are not infected. Infection of sensory and autonomic ganglia requires longer incubation times, as it reflects centrifugal propagation from the CNS to the periphery, via polysynaptic connections from sensory and autonomic neurons to the initially infected motoneurons. Virus is recovered from end organs only after the development of rabies because anterograde spread to end organs is likely mediated by passive diffusion, rather than active transport mechanisms.

Differential architecture of multisynaptic geniculo-cortical pathways to V4 and MT

Parallel visual pathways in the primate brain known as the dorsal and ventral streams receive retinal inputs mainly through the magnocellular (M) and parvocellular (P) layers of the lateral geniculate nucleus. Inputs from these layers terminate within distinct parts of layer 4C of V1 (visual area 1). Due to the complexity of M- and P-derived neural connectivity in V1 and higher visual areas, the contributions of M and P inputs to the dorsal and ventral streams remain unclear. Employing retrograde transsynaptic transport of rabies virus, we analyzed the architecture of bottom-up pathways toward ventral stream area V4 (visual area 4) and dorsal stream area MT (middle temporal area). We found that V4 receives both M and P inputs "trisynaptically" from layer 4C via layer 2/3 of V1, whereas MT receives M-dominant input "disynaptically" from layer 4C via layer 4B of V1. V4 also receives disynaptic input from the dorsal stream portion of V2 (visual area 2) (i.e., cytochrome oxidase-stained thick stripes). Moreover, both M and P inputs reach V4 trisynaptically and MT disynaptically through "short-cut" pathways that bypass layer 4C of V1. The differential patterns of multisynaptic geniculo-cortical pathways to V4 and MT imply distinct modes of information processing in the dorsal and ventral streams.

Preparatory activity and connectivity in dorsal anterior cingulate cortex for cognitive control

Dorsal anterior cingulate cortex (dACC) is composed of functionally distinct subregions that may contribute to the top-down control of response selection and preparation. Multiple motor areas have been identified in dACC, including an anterior zone implicated in conflict monitoring and a caudal zone involved in movement execution. This study tested the involvement of a third cingulate area, the posterior zone of dACC, in the top-down control of response selection and preparation. Sixteen healthy young adults were scanned with event-related functional magnetic resonance imaging while performing a cued go/no-go task that was designed to minimize response conflicts. The activation and functional connectivity of dACC were tested with standard convolution models and psychophysiological interaction analyses, respectively. Ready cues that informed the direction of the impending response triggered preparatory neural activity in the posterior zone of dACC and strengthened functional connectivity with the anterior and caudal zones of dACC, as well as perigenual anterior cingulate cortex, frontal operculum, dorsolateral prefrontal cortex, sensory association cortices, and extra-pyramidal motor areas. The preparatory cues activated dACC above and beyond the general arousing effects common to cues despite negligible conflict in the go/no-go task. The integration of cognitive, sensorimotor, and incentive signals in dACC places the region in an ideal position to select and prepare appropriate behavioral responses to achieve higher-level goals.

Effective connectivity of brain networks during self-initiated movement in Parkinson's disease

Patients with Parkinson's disease (PD) have difficulty in performing self-initiated movements. The neural mechanism of this deficiency remains unclear. In the current study, we used functional MRI (fMRI) and psychophysiological interaction (PPI) methods to investigate the changes in effective connectivity of the brain networks during performance of self-initiated movement in PD patients. Effective connectivity is defined as the influence one neuronal system exerts over another. fMRIs were acquired in 18 PD patients and in 18 age- and sex-matched healthy controls, when performing a self-initiated right hand tapping task. We chose the left primary motor cortex (M1), rostral supplementary motor area (pre-SMA), left premotor cortex (PMC), left putamen, and right cerebellum as index areas for PPI analysis. During the performance of self-initiated movement, connectivity between the putamen and M1, PMC, SMA, and cerebellum was decreased in PD patients compared to controls. In contrast, connections between the M1, pre-SMA, PMC, parietal cortex, and cerebellum were increased in PD patients compared to controls. In addition, the M1, pre-SMA, PMC, and cerebellum also had less connectivity with the dorsal lateral prefrontal cortex in PD. In PD patients, the effective connectivity between the putamen and M1, PMC, SMA, and cerebellum negatively correlated with the Unified Parkinson's Disease Rating Scale (UPDRS) motor scores; whereas the connectivity between the M1, pre-SMA, PMC, and cerebellum positively correlated with the UPDRS motor scores. Our findings demonstrate that the pattern of interactions of brain networks is disrupted in PD during performance of self-initiated movements. The striatum-cortical and striatum-cerebellar connections are weakened. In contrast, the connections between cortico-cerebellar motor regions are strengthened and may compensate for basal ganglia dysfunction. These altered interregional connections are more deviant when the disorder is more severe, and, therefore, our results give further insight into the explanation for the difficulty in performing self-initiated movements in PD.

Ascending multisynaptic pathways from the trigeminal ganglion to the anterior cingulate cortex

By means of retrograde transneuronal transport of rabies virus, ascending multisynaptic pathways from the trigeminal ganglion (TG) to the anterior cingulate cortex (ACC) were identified in the rat. After rabies injection into an electrophysiologically defined trigeminal projection region of the ACC, transsynaptic labeling of second-order neurons via the medial thalamus (including the parafascicular nucleus) was located in the spinal trigeminal nucleus pars caudalis. Third-order neuron labeling occurred in the TG. Most of these TG neurons were medium- or large-sized cells giving rise to myelinated Aδ or Aβ afferent fibers, respectively. By contrast, TG neurons labeled transsynaptically from the orofacial region of the primary somatosensory cortex contained many small cells associated with unmyelinated C afferent fibers. Furthermore, the TG neurons retrogradely labeled with fluorogold injected into the mental nerve were smaller in their sizes compared to those labeled with rabies. Our extracellular unit recordings revealed that a majority of ACC neurons responded to trigeminal nerve stimulation with latencies of shorter than 20ms. Thus, somatosensory information conveyed to the ACC by multisynaptic ascending pathways derived predominantly from myelinated primary afferents (i.e., the medial nociceptive system) and may be used to subserve affective-motivational aspects of pain. Lack of overlap with the lateral nociceptive system is notable and suggests that the medial and lateral nociceptive systems perform separate and non-overlapping functions.

Selection of prime actor in humans during bimanual object manipulation

In bimanual object manipulation tasks, people flexibly assign one hand as a prime actor while the other assists. Little is known, however, about the neural mechanisms deciding the role assignment. We addressed this issue in a task in which participants moved a cursor to hit targets on a screen by applying precisely coupled symmetrical opposing linear and twist forces on a tool held freely between the hands. In trials presented in an unpredictable order, the action of either the left or the right hand was spatially congruent with the cursor movements, which automatically rendered the left or right hand the dominant actor, respectively. Functional magnetic resonance imaging indicated that the hand-selection process engaged prefrontal cortical areas belonging to an executive control network presumed critical for judgment and decision-making and to a salience network attributed to evaluation of utility of actions. Task initiation, which involved switching between task sets, had a superordinate role with reference to hand selection. Behavioral and brain imaging data indicated that participants initially expressed two competing action representations, matching either mapping rule, before selecting the appropriate one based on the consequences of the initial manual actions. We conclude that implicit processes engaging the prefrontal cortex reconcile selections among action representations that compete for the establishment of a dominant actor in bimanual object manipulation tasks. The representation selected is the one that optimizes performance by relying on the superior capacity of the brain to process spatial congruent, as opposed to noncongruent, mappings between manual actions and desired movement goals.

Motor and non-motor projections from the cerebellum to rostrocaudally distinct sectors of the dorsal premotor cortex in macaques

In the caudal part of the dorsal premotor cortex of macaques (area F2), both anatomical and physiological studies have identified two rostrocaudally separate sectors. The rostral sector (F2r) is located medial to the genu of the arcuate sulcus, and the caudal sector (F2c) is located lateral to the superior precentral dimple. Here we examined the sites of origin of projections from the cerebellum to F2r and F2c. We applied retrograde transsynaptic transport of a neurotropic virus, CVS-11 of rabies virus, in macaque monkeys. Three days after rabies injections into F2r or F2c, neuronal labeling was found in the deep cerebellar nuclei mainly of the contralateral hemisphere. After the F2r injection, labeled cells were distributed primarily in the caudoventral portion of the dentate nucleus, whereas cells labeled after the F2c injection were distributed in the rostrodorsal portion of the dentate nucleus, and in the interpositus and fastigial nuclei. Four days after rabies injections, Purkinje cells were densely labeled in the lateral part of the cerebellar cortex. After the F2r injection, Purkinje cell labeling was confined to Crus I and II, whereas the labeling seen after the F2c injection was located broadly from lobules III to VIII, including Crus I and II. These results have revealed that F2c receives inputs from broader areas of the cerebellum than F2r, and that distinct portions of the deep cerebellar nuclei and the cerebellar cortex send major projections to F2r and F2c, suggesting that F2c and F2r may be under specific influences of the cerebellum.