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

Volitional inspiration is mediated by two independent output channels in the primary motor cortex

The diaphragm is a multifunctional muscle that mediates both autonomic and volitional inspiration. It is critically involved in vocalization, postural stability, and expulsive core-trunk functions, such as coughing, hiccups, and vomiting. In macaque monkeys, we used retrograde transneuronal transport of rabies virus injected into the left hemidiaphragm to identify cortical neurons that have multisynaptic connections with phrenic motoneurons. Our research demonstrates that representation of the diaphragm in the primary motor cortex (M1) is split into two spatially separate and independent sites. No cortico-cortical connections are known to exist between these two sites. One site is located dorsal to the arm representation within the central sulcus and the second site is lateral to the arm. The dual representation of the diaphragm warrants a revision to the somatotopic map of M1. The dorsal diaphragm representation overlaps with trunk and axial musculature. It is ideally situated to coordinate with these muscles during volitional inspiration and in producing intra-abdominal pressure gradients. The lateral site overlaps the origin of M1 projections to a laryngeal muscle, the cricothyroid. This observation suggests that the coordinated control of laryngeal muscles and the diaphragm during vocalization may be achieved, in part, by co-localization of their representations in M1. The neural organization of the two diaphragm sites underlies a new perspective for interpreting functional imaging studies of respiration and/or vocalization. Furthermore, our results provide novel evidence supporting the concept that overlapping output channels within M1 are a prerequisite for the formation of muscle synergies underlying fine motor control.

Resection of Low-Grade Gliomas in the Face Area of the Primary Motor Cortex and Neurological Outcome

OBJECTIVE

During surgery on low-grade gliomas (LGG), reliable data relevant to the primary motor cortex (M1) for the face area are lacking. We analyzed the impact of tumor removal within the M1 face area on neurological deficits.

METHODS

We included LGG patients with resection within the M1 face area between May 2012 and November 2019. The primary endpoint was postoperative facial motor function. Secondary endpoints were postoperative aphasia, dysarthria, and dysphagia. Surgery was performed either with the awake protocol or under anesthesia with continuous dynamic mapping. The alarm criteria were speech arrest or a mapping threshold of 3 mA or less. Resection was completed in five patients. The resection was stopped due to the alarm criteria in three patients and for other reasons (vascular supply, patient performance) in four patients. A total of 66.7% (n = 8) presented with new-onset facial paresis (62.5% left LGG) and 41.7% (n = 5) with aphasia (all left LGG) postoperatively. After one year, all eight patients had recovered from the facial paresis. Tumor removal within the M1 face area was not associated with permanent facial motor deficits.

Towards a somatosensory theory of speech perception

Speech perception is known to be a multimodal process, relying not only on auditory input but also on the visual system and possibly on the motor system as well. To date there has been little work on the potential involvement of the somatosensory system in speech perception. In the present review, we identify the somatosensory system as another contributor to speech perception. First, we argue that evidence in favor of a motor contribution to speech perception can just as easily be interpreted as showing somatosensory involvement. Second, physiological and neuroanatomical evidence for auditory-somatosensory interactions across the auditory hierarchy indicates the availability of a neural infrastructure that supports somatosensory involvement in auditory processing in general. Third, there is accumulating evidence for somatosensory involvement in the context of speech specifically. In particular, tactile stimulation modifies speech perception, and speech auditory input elicits activity in somatosensory cortical areas. Moreover, speech sounds can be decoded from activity in somatosensory cortex; lesions to this region affect perception, and vowels can be identified based on somatic input alone. We suggest that the somatosensory involvement in speech perception derives from the somatosensory-auditory pairing that occurs during speech production and learning. By bringing together findings from a set of studies that have not been previously linked, the present article identifies the somatosensory system as a presently unrecognized contributor to speech perception.

Patterns of grey and white matter changes differ between bulbar and limb onset amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disease that is characterized by a high heterogeneity in patients' disease course. Patients with bulbar onset of symptoms (b-ALS) have a poorer prognosis than patients with limb onset (l-ALS). However, neuroimaging correlates of the assumed biological difference between b-ALS and l-ALS may have been obfuscated by patients' diversity in the disease course. We conducted Voxel-Based-Morphometry (VBM) and Tract-Based-Spatial-Statistics (TBSS) in a group of 76 ALS patients without clinically relevant cognitive deficits. The subgroups of 26 b-ALS and 52 l-ALS patients did not differ in terms of disease Phase or disease aggressiveness according to the D50 progression model. VBM analyses showed widespread ALS-related changes in grey and white matter, that were more pronounced for b-ALS. TBSS analyses revealed that b-ALS was predominantly characterized by frontal fractional anisotropy decreases. This demonstrates a higher degree of neurodegenerative burden for the group of b-ALS patients in comparison to l-ALS. Correspondingly, higher bulbar symptom burden was associated with right-temporal and inferior-frontal grey matter density decreases as well as fractional anisotropy decreases in inter-hemispheric and long association tracts. Contrasts between patients in Phase I and Phase II further revealed that b-ALS was characterized by an early cortical pathology and showed a spread only outside primary motor regions to frontal and temporal areas. In contrast, l-ALS showed ongoing structural integrity loss within primary motor-regions until Phase II. We therefore provide a strong rationale to treat both onset types of disease separately in ALS studies.

Reciprocal cortical activation patterns during incisal and molar biting correlated with bite force levels: an fMRI study

In humans, the incisors and molars have distinct functions during mastication, analogous to the two main types of handgrip, the precision and power grips. In the present study, we investigated cortical activation and masticatory muscle activity during incisal and molar biting via simultaneous functional magnetic resonance imaging and electromyogram (EMG) recordings. We conducted recordings in 15 healthy adult participants while they performed incisal and molar biting tasks at three step-wise force levels using two custom-made splints. Regarding the results of the ROI analysis, we found a significantly stronger positive linear correlation between the blood oxygenation level dependent signal and EMG activity during molar biting than incisal biting, which was particularly prominent in the primary sensorimotor cortex and the cerebellum. We also found a significantly stronger negative linear correlation during incisal biting than molar biting, which was particularly prominent in the rostral cingulate motor area, superior frontal gyrus, and caudate nucleus. These findings indicate that molar biting enables powerful chewing: brain activity in several brain areas related to motor function was increased with increasing bite force levels, while incisal biting enables fine motor control: brain activity in several brain areas related to motor control was increased with reduced bite force levels.

Optimization of macaque brain DMRI connectome by neuron tracing and myelin stain data

Accurate assessment of connectional anatomy of primate brains can be an important avenue to better understand the structural and functional organization of brains. To this end, numerous connectome projects have been initiated to create a comprehensive map of the connectional anatomy over a large spatial expanse. Tractography based on diffusion MRI (dMRI) data has been used as a tool by many connectome projects in that it is widely used to visualize axonal pathways and reveal microstructural features on living brains. However, the measures obtained from dMRI are indirect inference of microstructures. This intrinsic limitation reduces the reliability of dMRI in constructing connectomes for brains. In this work, we proposed a framework to increase the accuracy of constructing a dMRI-based connectome on macaque brains by integrating meso-scale connective information from tract-tracing data and micro-scale axonal orientation information from myelin stain data. Our results suggest that this integrative framework could advance the mapping accuracy of dMRI based connections and axonal pathways, and demonstrate the prospect of the proposed framework in constructing a large-scale connectome on living primate brains.

Reward activations and face fields in monkey cingulate motor areas

Several premotor areas have been identified within primate cingulate cortex; however their function is yet to be uncovered. Recent brain imaging work in humans revealed a topographic anatomofunctional overlap between feedback processing during exploratory behaviors and the corresponding body fields in the rostral cingulate motor area (RCZa), suggesting an embodied representation of feedback. In particular, a face field in RCZa processes juice feedback. Here we tested an extension of the embodied principle in which unexpected or relevant information obtained through the eye or the face would be processed by face fields in cingulate motor areas, and whether this applied to monkey cingulate cortex. We show that activations for juice reward, eye movement, eye blink, and tactile stimulation on the face overlap over two subfields within the cingulate sulcus likely corresponding to the rostral and caudal cingulate motor areas. This suggests that in monkeys as is the case in humans, behaviorally relevant information is processed through multiple cingulate body/effector maps.

NEW & NOTEWORTHY What is the role of cingulate motor areas? In this study we observed in monkeys that, as in humans, neural responses to face-related events, juice reward, eye movement, eye blink, and tactile stimulations, clustered redundantly in two separate cingulate subfields. This suggests that behaviorally relevant information is processed by multiple cingulate effector maps. Importantly, this overlap supports the principle that the cingulate cortex processes feedback based on where it is experienced on the body.

Cytoarchitecture and cortical connections of the anterior insula and adjacent frontal motor fields in the rhesus monkey

The cytoarchitecture and cortical connections of the ventral motor region are investigated using Nissl, and NeuN staining methods and the fluorescent retrograde tract tracing technique in the rhesus monkey. On the basis of gradual laminar differentiation, it is shown that the ventral motor region stems from the ventral proisocortical area (anterior insula and dorsal Sylvian opercular region). The cytoarchitecture of the ventral motor region is shown to progress in three lines, as we have recently shown for the dorsal motor region. Namely, root (anterior insular and dorsal Sylvian opercular area ProM), belt (ventral premotor cortex) and core (precentral motor cortex) lines. This stepwise architectonic organization is supported by the overall patterns of corticocortical connections. Areas in each line are sequentially interconnected (intralineal connections) and all lines are interconnected (interlinear connections). Moreover, root areas, as well as some of the belt areas of the ventral and dorsal trend are interconnected. The ventral motor region is also connected with the ventral somatosensory areas in a topographic manner. The root and belt areas of ventral motor region are connected with paralimbic, multimodal and prefrontal (outer belt) areas. In contrast, the core area has a comparatively more restricted pattern of corticocortical connections. This architectonic and connectional organization is consistent in part, with the functional organization of the ventral motor region as reported in behavioral and neuroimaging studies which include the mediation of facial expression and emotion, communication, phonic articulation, and language in human.

Superficial white matter fiber systems impede detection of long-range cortical connections in diffusion MR tractography

In vivo tractography based on diffusion magnetic resonance imaging (dMRI) has opened new doors to study structure-function relationships in the human brain. Initially developed to map the trajectory of major white matter tracts, dMRI is used increasingly to infer long-range anatomical connections of the cortex. Because axonal projections originate and terminate in the gray matter but travel mainly through the deep white matter, the success of tractography hinges on the capacity to follow fibers across this transition. Here we demonstrate that the complex arrangement of white matter fibers residing just under the cortical sheet poses severe challenges for long-range tractography over roughly half of the brain. We investigate this issue by comparing dMRI from very-high-resolution ex vivo macaque brain specimens with histological analysis of the same tissue. Using probabilistic tracking from pure gray and white matter seeds, we found that ∼50% of the cortical surface was effectively inaccessible for long-range diffusion tracking because of dense white matter zones just beneath the infragranular layers of the cortex. Analysis of the corresponding myelin-stained sections revealed that these zones colocalized with dense and uniform sheets of axons running mostly parallel to the cortical surface, most often in sulcal regions but also in many gyral crowns. Tracer injection into the sulcal cortex demonstrated that at least some axonal fibers pass directly through these fiber systems. Current and future high-resolution dMRI studies of the human brain will need to develop methods to overcome the challenges posed by superficial white matter systems to determine long-range anatomical connections accurately.

Cortical innervation of the hypoglossal nucleus in the non-human primate (Macaca mulatta)

The corticobulbar projection to the hypoglossal nucleus was studied from the frontal, parietal, cingulate, and insular cortices in the rhesus monkey by using high-resolution anterograde tracers and stereology. The hypoglossal nucleus received bilateral input from the face/head region of the primary (M1), ventrolateral pre- (LPMCv), supplementary (M2), rostral cingulate (M3), and caudal cingulate (M4) motor cortices. Additional bilateral corticohypoglossal projections were found from the dorsolateral premotor cortex (LPMCd), ventrolateral proisocortical motor area (ProM), ventrolateral primary somatosensory cortex (S1), rostral insula, and pregenual region of the anterior cingulate gyrus (areas 24/32). Dense terminal projections arose from the ventral region of M1, and moderate projections from LPMCv and rostral part of M2, with considerably fewer hypoglossal projections arising from the other cortical regions. These findings demonstrate that extensive regions of the non-human primate cerebral cortex innervate the hypoglossal nucleus. The widespread and bilateral nature of this corticobulbar connection suggests recovery of tongue movement after cortical injury that compromises a subset of these areas, may occur from spared corticohypoglossal projection areas located on the lateral, as well as medial surfaces of both hemispheres. Since functional imaging studies have shown that homologous cortical areas are activated in humans during tongue movement tasks, these corticobulbar projections may exist in the human brain.

Midcingulate Motor Map and Feedback Detection: Converging Data from Humans and Monkeys

The functional and anatomical organization of the cingulate cortex across primate species is the subject of considerable and often confusing debate. The functions attributed to the midcingulate cortex (MCC) embrace, among others, feedback processing, pain, salience, action-reward association, premotor functions, and conflict monitoring. This multiplicity of functional concepts suggests either unresolved separation of functional contributions or integration and convergence. We here provide evidence from recent experiments in humans and from a meta-analysis of monkey data that MCC feedback-related activity is generated in the rostral cingulate premotor area by specific body maps directly related to the modality of feedback. As such, we argue for an embodied mechanism for adaptation and exploration in MCC. We propose arguments and precise tools to resolve the origins of performance monitoring signals in the medial frontal cortex, and to progress on issues regarding homology between human and nonhuman primate cingulate cortex.

Patterns of cortical input to the primary motor area in the marmoset monkey

In primates the primary motor cortex (M1) forms a topographic map of the body, whereby neurons in the medial part of this area control movements involving trunk and hindlimb muscles, those in the intermediate part control movements involving forelimb muscles, and those in the lateral part control movements of facial and other head muscles. This topography is accompanied by changes in cytoarchitectural characteristics, raising the question of whether the anatomical connections also vary between different parts of M1. To address this issue, we compared the patterns of cortical afferents revealed by retrograde tracer injections in different locations within M1 of marmoset monkeys. We found that the entire extent of this area is unified by projections from the dorsocaudal and medial subdivisions of premotor cortex (areas 6DC and 6M), from somatosensory areas 3a, 3b, 1/2, and S2, and from posterior parietal area PE. While cingulate areas projected to all subdivisions, they preferentially targeted the medial part of M1. Conversely, the ventral premotor areas were preferentially connected with the lateral part of M1. Smaller but consistent inputs originated in frontal area 6DR, ventral posterior parietal cortex, the retroinsular cortex, and area TPt. Connections with intraparietal, prefrontal, and temporal areas were very sparse, and variable. Our results demonstrate that M1 is unified by a consistent pattern of major connections, but also shows regional variations in terms of minor inputs. These differences likely reflect requirements for control of voluntary movement involving different body parts.

In vivo architectonics: a cortico-centric perspective

Recent advances in noninvasive structural imaging have opened up new approaches to cortical parcellation, many of which are described in this special issue on In Vivo Brodmann Mapping. In this introductory article, we focus on the emergence of cortical myelin maps as a valuable way to assess cortical organization in humans and nonhuman primates. We demonstrate how myelin maps are useful in three general domains: (i) as a way to identify cortical areas and functionally specialized regions in individuals and group averages; (ii) as a substrate for improved intersubject registration; and (iii) as a basis for interspecies comparisons. We also discuss how myelin-based cortical parcellation is complementary in important ways to connectivity-based parcellation using functional MRI or diffusion imaging and tractography. These observations and perspectives provide a useful background and context for other articles in this special issue.

fMRI Cortical Correlates of Spontaneous Eye Blinks in the Nonhuman Primate

Eyeblinks are defined as a rapid closing and opening of the eyelid. Three types of blinks are defined: spontaneous, reflexive, and voluntary. Here, we focus on the cortical correlates of spontaneous blinks, using functional magnetic resonance imaging (fMRI) in the nonhuman primate. Our observations reveal an ensemble of cortical regions processing the somatosensory, proprioceptive, peripheral visual, and possibly nociceptive consequences of blinks. These observations indicate that spontaneous blinks have consequences on the brain beyond the visual cortex, possibly contaminating fMRI protocols that generate in the participants heterogeneous blink behaviors. This is especially the case when these protocols induce (nonunusual) eye fatigue and corneal dryness due to demanding fixation requirements, as is the case here. Importantly, no blink related activations were observed in the prefrontal and parietal blinks motor command areas nor in the prefrontal, parietal, and medial temporal blink suppression areas. This indicates that the absence of activation in these areas is not a signature of the absence of blink contamination in the data. While these observations increase our understanding of the neural bases of spontaneous blinks, they also strongly call for new criteria to identify whether fMRI recordings are contaminated by a heterogeneous blink behavior or not.

The facial motor system

Facial movements support a variety of functions in human behavior. They participate in automatic somatic and visceral motor programs, they are essential in producing communicative displays of affective states and they are also subject to voluntary control. The multiplicity of functions of facial muscles, compared to limb muscles, is reflected in the heterogeneity of their anatomical and histological characteristics that goes well beyond the conventional classification in single facial muscles. Such parcellation in different functional muscular units is maintained throughout the central representation of facial movements from the brainstem up to the neocortex. Facial movements peculiarly lack a conventional proprioceptive feedback system, which is only in part vicariated by cutaneous or auditory afferents. Facial motor activity is the main marker of endogenous affective states and of the affective valence of external stimuli. At the cortical level, a complex network of specialized motor areas supports voluntary facial movements and, differently from upper limb movements, in such network there does not seem to be a prime actor in the primary motor cortex.

Cartography and connectomes

The past 25 years have seen great progress in parcellating the cerebral cortex into a mosaic of many distinct areas in mice, monkeys, and humans. Quantitative studies of interareal connectivity have revealed unexpectedly many pathways and a wide range of connection strengths in mouse and macaque cortex. In humans, advances in analyzing "structural" and "functional" connectivity using powerful but indirect noninvasive neuroimaging methods are yielding intriguing insights about brain circuits, their variability across individuals, and their relationship to behavior.

Posed versus spontaneous facial expressions are modulated by opposite cerebral hemispheres

Clinical research has indicated that the left face is more expressive than the right face, suggesting that modulation of facial expressions is lateralized to the right hemisphere. The findings, however, are controversial because the results explain, on average, approximately 4% of the data variance. Using high-speed videography, we sought to determine if movement-onset asymmetry was a more powerful research paradigm than terminal movement asymmetry. The results were very robust, explaining up to 70% of the data variance. Posed expressions began overwhelmingly on the right face whereas spontaneous expressions began overwhelmingly on the left face. This dichotomy was most robust for upper facial expressions. In addition, movement-onset asymmetries did not predict terminal movement asymmetries, which were not significantly lateralized. The results support recent neuroanatomic observations that upper versus lower facial movements have different forebrain motor representations and recent behavioral constructs that posed versus spontaneous facial expressions are modulated preferentially by opposite cerebral hemispheres and that spontaneous facial expressions are graded rather than non-graded movements.

Cytoarchitecture and cortical connections of the anterior cingulate and adjacent somatomotor fields in the rhesus monkey

The cytoarchitecture and cortical connections of the anterior cingulate, medial and dorsal premotor, and precentral region are investigated using the Nissl and NeuN staining methods and the fluorescent retrograde tract tracing technique. There is a gradual stepwise laminar change in the cytoarchitectonic organization from the proisocortical anterior cingulate region, through the lower and upper banks of the cingulate sulcus, to the dorsolateral isocortical premotor and precentral motor regions of the frontal lobe. These changes are characterized by a gradational emphasis on the lower stratum layers (V and VI) in the proisocortical cingulate region to the upper stratum layers (II and III) in the premotor and precentral motor region. This is accompanied by a progressive widening of layers III and VI, a poorly delineated border between layers III and V and a sequential increase in the size of layer V neurons culminating in the presence of giant Betz cells in the precentral motor region. The overall patterns of corticocortical connections paralleled the sequential changes in cytoarchitectonic organization. The proisocortical areas have connections with cingulate motor, supplementary motor, premotor and precentral motor areas on the one hand and have widespread connections with the frontal, parietal, temporal and multimodal association cortex and limbic regions on the other. The dorsal premotor areas have connections with the proisocortical areas including cingulate motor areas and supplementary motor area on the one hand, and premotor and precentral motor cortex on the other. Additionally, this region has significant connections with posterior parietal cortex and limited connections with prefrontal, limbic and multimodal regions. The precentral motor cortex also has connections with the proisocortical areas and premotor areas. Its other connections are limited to the somatosensory regions of the parietal lobe. Since the isocortical motor areas on the dorsal convexity mediate voluntary motor function, their close connectional relationship with the cingulate areas form a pivotal limbic-motor interface that could provide critical sources of cognitive, emotional and motivational influence on complex motor function.

Time Course of Cortical Plasticity After Facial Nerve Palsy

Background. Functional connectivity is defined as the temporal correlation between spatially remote neurophysiological events. This method has become particularly useful for studying neuroplasticity to detect changes in the collaboration of brain areas during cortical reorganization. Methods. In this article, the authors longitudinally studied voxel-based morphometry and resting state functional magnetic resonance imaging 10 times in 1 patient during the course of Bell palsy (idiopathic facial nerve palsy) up to complete clinical recovery. Results. Morphometric analysis revealed a significant alteration in the face area of the primary motor cortex (M1) contralateral to the paretic face, with an initial increase in gray matter concentration. Functional connectivity analysis between the M1 and other parts of the facial motor network revealed acutely disrupted intrahemispheric connectivity but unaltered interhemispheric connectivity. The disrupted functional connectivity was most pronounced on the day of the onset of symptoms, with a subsequent return toward normal during the course of recovery. This time course was found to differ between the selected parts of the facial motor network. However, the increase in functional connectivity strength preceded clinical recovery in all areas and reached a stable level before the patient fully recovered. Conclusion. These results demonstrate that recovery from facial nerve palsy is complemented by cortical reorganization, with pronounced changes of functional connectivity that precede clinical recovery.

Discovering the somatotopic organization of the motor areas of the medial wall using low-frequency BOLD fluctuations

This study explored the somatotopy of the motor areas of the medial wall of the cerebral hemisphere, in the human brain. In a sample of 16 healthy participants, we drew 9 regions of interest (ROI) over the primary motor area (M1), each corresponding to a well-known somatic representation. Using functional magnetic resonance imaging, we investigated the resting state functional connectivity between each selected ROI and the motor areas of the medial wall. The main finding was the identification of a rostrocaudal gradient of connectivity in which the more we move from cranial to caudal body representation areas in M1, the more the corresponding connected area in the medial wall is shifted rostrocaudally, confirming the somatotopic schema found in the SMA. We also reanalyzed data obtained in a previous experiment, we performed using hand and foot motor tasks; the reanalysis consisted in traditional BOLD and functional connectivity analyses. Finally, we performed a meta-analysis of 28 studies of hand and foot motor tasks, mapping their cerebral representations using the tools provided by the Brainmap database. All data converge in confirming a somatotopic representation of the medial wall motor areas, with hand representation placed more rostrally and ventrally than that of the foot.

Correlated evolution of brain regions involved in producing and processing facial expressions in anthropoid primates

Anthropoid primates are distinguished from other mammals by having relatively large primary visual cortices (V1) and complex facial expressions. We present a comparative test of the hypothesis that facial expression processing coevolved with the expansion of V1 in anthropoids. Previously published data were analysed using phylogenetic comparative methods. The results of our study suggest a pattern of correlated evolution linking social group size, facial motor control and cortical visual processing in catarrhines, but not platyrrhines. Catarrhines that live in relatively large social groups tended to have relatively large facial motor nuclei, and relatively large primary visual cortices. We conclude that catarrhine brains are adapted for producing and processing complex facial displays.

Transdural doppler ultrasonography monitors cerebral blood flow changes in relation to motor tasks

Monitoring changes in cerebral blood flow in association with neuronal activity has widely been used to evaluate various brain functions. However, current techniques do not directly measure blood flow changes in specified blood vessels. The present study identified arterioles within the cerebral cortex by echoencephalography and color Doppler imaging, and then measured blood flow velocity (BFV) changes in pulsed-wave Doppler mode. We applied this "transdural Doppler ultrasonography (TDD)" to examine BFV changes in the cortical motor-related areas of monkeys during the performance of unimanual (right or left) and bimanual key-press tasks. BFV in the primary motor cortex (MI) was increased in response to contralateral movement. In each of the unimanual and bimanual tasks, bimodal BFV increases related to both the instruction signal and the movement were observed in the supplementary motor area (SMA). Such BFV changes in the SMA were prominent during the early stage of task training and gradually decreased with improvements in task performance, leaving those in the MI unchanged. Moreover, BFV changes in the SMA depended on task difficulty. The present results indicate that TDD is useful for evaluating regional brain functions.

Experience-based priming of body parts: a study of action imitation

Two important dimensions of action are the movement and the body part with which the movement is effected. Experiment 1 tested whether automatic imitation is sensitive to the body part dimension of action. We found that hand and foot movements were selectively primed by observation of a corresponding, task-irrelevant effector in motion. Experiment 2 used this body part priming effect to investigate the role of sensorimotor learning in the development of imitation. The results showed that incompatible training, in which observation of hand movements was paired with execution of foot movements and vice versa, led to a greater reduction in body part priming than compatible training, in which subjects experienced typical contingencies between observation and execution of hand and foot movements. These findings are consistent with the assumption that overt behavioral imitation is mediated by the mirror neuron system, which is somatotopically organized. Our results also support the hypothesis that the development of imitation and the mirror neuron system are driven by correlated sensorimotor learning.

Primary face motor area as the motor representation of articulation

No clinical data have yet been presented to show that a lesion localized to the primary motor area (M1) can cause severe transient impairment of articulation, although a motor representation for articulation has been suggested to exist within M1. Here we describe three cases of patients who developed severe dysarthria, temporarily mimicking speech arrest or aphemia, due to a localized brain lesion near the left face representation of the human primary motor cortex (face-M1). Speech was slow, effortful, lacking normal prosody, and more affected than expected from the degree of facial or tongue palsy. There was a mild deficit in tongue movements in the sagittal plane that impaired palatolingual contact and rapid tongue movements. The speech disturbance was limited to verbal output, without aphasia or orofacial apraxia. Overlay of magnetic resonance images revealed a localized cortical region near face-M1, which displayed high intensity on diffusion weighted images, while the main portion of the corticobulbar fibers arising from the lower third of the motor cortex was preserved. The cases suggest the existence of a localized brain region specialized for articulation near face-M1. Cortico-cortical fibers connecting face-M1 with the lower premotor areas including Broca's area may also be important for articulatory control.

Amygdala interconnections with the cingulate motor cortex in the rhesus monkey

Amygdala interconnections with the cingulate motor cortices were investigated in the rhesus monkey. Using multiple tracing approaches, we found a robust projection from the lateral basal nucleus of the amygdala to Layers II, IIIa, and V of the rostral cingulate motor cortex (M3). A smaller source of amygdala input arose from the accessory basal, cortical, and lateral nuclei, which targeted only the rostral region of M3. We also found a light projection from the lateral basal nucleus to the same layers of the caudal cingulate motor cortex (M4). Experiments examining this projection to cingulate somatotopy using combined neural tracing strategies and stereology to estimate the total number of terminal-like immunoreactive particles demonstrated that the amygdala projection terminates heavily in the face representation of M3 and moderately in its arm representation. Fewer terminal profiles were found in the leg representation of M3 and the face, arm, and leg representations of M4. Anterograde tracers placed directly into M3 and M4 revealed the amygdala connection to be reciprocal and documented corticofugal projections to the facial nucleus, surrounding pontine reticular formation, and spinal cord. Clinically, such pathways would be in a position to contribute to mediating movements in the face, neck, and upper extremity accompanying medial temporal lobe seizures that have historically characterized this syndrome. Alterations within or disruption of the amygdalo-cingulate projection to the rostral part of M3 may also have an adverse effect on facial expression in patients presenting with neurological or neuropsychiatric abnormalities of medial temporal lobe involvement. Finally, the prominent amygdala projection to the face region of M3 may significantly influence the outcome of higher-order facial expressions associated with social communication and emotional constructs such as fear, anger, happiness, and sadness.

Ipsilateral cortical connections of dorsal and ventral premotor areas in New World owl monkeys

In order to compare connections of premotor cortical areas of New World monkeys with those of Old World macaque monkeys and prosimian galagos, we placed injections of fluorescent tracers and wheat germ agglutinin-horseradish peroxidase (WGA-HRP) in dorsal (PMD) and ventral (PMV) premotor areas of owl monkeys. Motor areas and injection sites were defined by patterns of movements electrically evoked from the cortex with microelectrodes. Labeled neurons and axon terminals were located in brain sections cut either in the coronal plane or parallel to the surface of flattened cortex, and they related to architectonically and electrophysiologically defined cortical areas. Both the PMV and PMD had connections with the primary motor cortex (M1), the supplementary motor area (SMA), cingulate motor areas, somatosensory areas S2 and PV, and the posterior parietal cortex. Only the PMV had connections with somatosensory areas 3a, 1, 2, PR, and PV. The PMD received inputs from more caudal portions of the cortex of the lateral sulcus and more medial portions of the posterior parietal cortex than the PMV. The PMD and PMV were only weakly interconnected. New World owl monkeys, Old World macaque monkeys, and galagos share a number of PMV and PMD connections, suggesting preservation of a common sensorimotor network from early primates. Comparisons of PMD and PMV connectivity with the cortex of the lateral sulcus and posterior parietal cortex of owl monkeys, galagos, and macaques help identify areas that could be homologous.

Input-output organization of jaw movement-related areas in monkey frontal cortex

The brain mechanisms underlying mastication are not fully understood. To address this issue, we analyzed the distribution patterns of cortico-striatal and cortico-brainstem axon terminals and the origin of thalamocortical and intracortical fibers by injecting anterograde/retrograde tracers into physiologically and morphologically defined jaw movement-related cortical areas. Four areas were identified in the macaque monkey: the primary and supplementary orofacial motor areas (MIoro and SMAoro) and the principal and deep parts of the cortical masticatory area (CMaAp and CMaAd), where intracortical microstimulation produced single twitch-like or rhythmic jaw movements, respectively. Tracer injections into these areas labeled terminals in the ipsilateral putamen in a topographic fashion (MIoro vs. SMAoro and CMaAp vs. CMaAd), in the lateral reticular formation and trigeminal sensory nuclei contralaterally (MIoro and CMaAp) or bilaterally (SMAoro) in a complex manner of segregation vs. overlap, and in the medial parabranchial and Kölliker-Fuse nuclei contralaterally (CMaAd). The MIoro and CMaAp received thalamic projections from the ventrolateral and ventroposterolateral nuclei, the SMAoro from the ventroanterior and ventrolateral nuclei, and the CMaAd from the ventroposteromedial nucleus. The MIoro, SMAoro, CMaAp, and CMaAd received intracortical projections from the ventral premotor cortex and primary somatosensory cortex, the ventral premotor cortex and rostral cingulate motor area, the ventral premotor cortex and area 7b, and various sensory areas. In addition, the MIoro and CMaAp received projections from the three other jaw movement-related areas. Our results suggest that the four jaw movement-related cortical areas may play important roles in the formation of distinctive masticatory patterns.

Callosal connections of dorsal versus ventral premotor areas in the macaque monkey: a multiple retrograde tracing study

Background

The lateral premotor cortex plays a crucial role in visually guided limb movements. It is divided into two main regions, the dorsal (PMd) and ventral (PMv) areas, which are in turn subdivided into functionally and anatomically distinct rostral (PMd-r and PMv-r) and caudal (PMd-c and PMv-c) sub-regions. We analyzed the callosal inputs to these premotor subdivisions following 23 injections of retrograde tracers in eight macaque monkeys. In each monkey, 2–4 distinct tracers were injected in different areas allowing direct comparisons of callosal connectivity in the same brain.

Results

Based on large injections covering the entire extent of the corresponding PM area, we found that each area is strongly connected with its counterpart in the opposite hemisphere. Callosal connectivity with the other premotor areas, the primary motor cortex, prefrontal cortex and somatosensory cortex varied from one area to another. The most extensive callosal inputs terminate in PMd-r and PMd-c, with PMd-r strongly connected with prefrontal cortex. Callosal inputs to PMv-c are more extensive than those to PMv-r, whose connections are restricted to its counterpart area. Quantitative analysis of labelled cells confirms these general findings, and allows an assessment of the relative strength of callosal inputs.

Conclusion

PMd-r and PMv-r receive their strongest callosal inputs from their respective counterpart areas, whereas PMd-c and PMv-c receive strong inputs from heterotopic areas as well (namely from PMd-r and PMv-r, respectively). Finally, PMd-r stands out as the lateral premotor area with the strongest inputs from the prefrontal cortex, and only the PMd-c and PMv-c receive weak callosal inputs from M1.

Ipsilateral cortical connections of motor, premotor, frontal eye, and posterior parietal fields in a prosimian primate, Otolemur garnetti

The ipsilateral connections of motor areas of galagos were determined by injecting tracers into primary motor cortex (M1), dorsal premotor area (PMD), ventral premotor area (PMV), supplementary motor area (SMA), and frontal eye field (FEF). Other injections were placed in frontal cortex and in posterior parietal cortex to define the connections of motor areas further. Intracortical microstimulation was used to identify injection sites and map motor areas in the same cases. The major connections of M1 were with premotor cortex, SMA, cingulate motor cortex, somatosensory areas 3a and 1, and the rostral half of posterior parietal cortex. Less dense connections were with the second (S2) and parietal ventral (PV) somatosensory areas. Injections in PMD labeled neurons across a mediolateral belt of posterior parietal cortex extending from the medial wall to lateral to the intraparietal sulcus. Other inputs came from SMA, M1, PMV, and adjoining frontal cortex. PMV injections labeled neurons across a large zone of posterior parietal cortex, overlapping the region projecting to PMD but centered more laterally. Other connections were with M1, PMD, and frontal cortex and sparsely with somatosensory areas 3a, 1-2, S2, and PV. SMA connections were with medial posterior parietal cortex, cingulate motor cortex, PMD, and PMV. An FEF injection labeled neurons in the intraparietal sulcus. Injections in posterior parietal cortex revealed that the rostral half receives somatosensory inputs, whereas the caudal half receives visual inputs. Thus, posterior parietal cortex links visual and somatosensory areas with motor fields of frontal cortex.

Orofacial somatomotor responses in the macaque monkey homologue of Broca's area

In the ventrolateral frontal lobe of the human brain there is a distinct entity, cytoarchitectonic area 44 (Broca's area), which is crucial in speech production. There has been controversy over whether monkeys possess an area comparable to human area 44. We have addressed this question in the macaque monkey by combining quantitative architectonic analysis of the cortical areas within the ventrolateral frontal region with electrophysiological recording of neuron activity and electrical intracortical microstimulation. Here we show that, immediately in front of the ventral part of the agranular premotor cortical area 6, there is a distinct cortical area that is architectonically comparable to human area 44 and that this monkey area 44 is involved with the orofacial musculature. We suggest that area 44 might have evolved originally as an area exercising high-level control over orofacial actions, including those related to communicative acts, and that, in the human brain, area 44 eventually also came to control certain aspects of the speech act.

Afferent cortical connections of the motor cortical larynx area in the rhesus monkey

The present study describes the cortical input into the motor cortical larynx area. The retrograde tracer horseradish peroxidase-conjugated wheat germ agglutinin was injected into the electrophysiologically identified motor cortical larynx area in three rhesus monkeys (Macaca mulatta). Retrogradely labeled cells were found in the surrounding premotor cortex (areas 6V and 6D), primary motor cortex (area 4), primary somatosensory cortex (areas 3, 1 and 2), anterior and posterior secondary somatosensory cortex and the probable homologue of Broca's area (areas 44 and 45); furthermore, labeling was found in the supplementary motor area, anterior and posterior cingulate cortex (areas 24 and 23), prefrontal and orbital frontal cortex (areas 8A, 46V, 47/12L, 47/12O, 13), agranular, dysgranular and granular insula as well as in the cortex within the upper bank of the middle third of the superior temporal sulcus (area TPO). The majority of these regions are reciprocally connected with the motor cortical larynx area [Brain Res 949 (2000) 23]. The laryngeal motor cortical input is discussed in relation to the connections of other motor cortical areas and its role in vocal control.

The motor cortex and facial expression: new insights from neuroscience

BACKGROUND

For more than a century, unusual and complex deficits in facial expression have been known to occur following localized brain damage. Some brain injuries leave the face with pronounced alterations in affect whereas others result in movement disorders such as blepharospasm and Meige syndrome. There is also a historic trail of clinical observations that document deficits in either voluntary or emotional control of the facial muscles following central nervous system damage.

REVIEW SUMMARY

Recent studies in the nonhuman primate cerebral cortex reveal the existence of multiple cortical facial representations in the frontal lobe and adjacent anterior cingulate cortex. These comprise the facial representation of the primary motor cortex (M1), ventral lateral premotor cortex (LPMCv), supplementary motor cortex (M2), rostral cingulate motor cortex (M3), and caudal cingulate motor cortex (M4). Homologous facial representations reside in the human brain based on observations following cortical stimulation, functional neuroimaging, and localized surgical resection. In the nonhuman primate, all these facial representations have been found to be directly interconnected through topographically organized corticocortical connections, and each facial area has also been found to send direct corticobulbar projections to the facial motor nucleus. The facial representations of M2 and M3 are both located on the medial wall of the hemisphere, in the vascular territory of the anterior cerebral artery. Both preferentially give rise to bilateral projections to parts of the facial nucleus that innervate the upper facial musculature as demonstrated in the monkey. The facial representation of M1, LPMCv, and M4 preferentially give rise to contralateral axonal projections ending in parts of the facial nucleus that innervate the lower facial musculature. The facial representation of M1 and LPMCv both reside in the vascular territory of the middle cerebral artery (MCA). The classic clinical presentation of paralysis in the contralateral lower facial musculature and intact bilateral upper facial musculature following typical MCA in infarction in the human parallels this mapping pattern of corticobulbar connections found in the nonhuman primate.

CONCLUSIONS

Facial movements are undoubtedly under the powerful influence of the cerebral cortex and are essential for the appropriate execution of many important functions such as mastication, swallowing, and social interaction, including speech and nonverbal communication. This information provides a theoretic template for interpreting the clinical effects of neuropathologic disease and localized cortical trauma on facial movements.

A Functional Connection Between Inferior Frontal Gyrus and Orofacial Motor Cortex in Human

The inferior frontal gyrus (IFG) of humans is known to play a critical role in speech production. The IFG is a highly convoluted and cytoarchitectonically diverse structure, classically forming 3 subgyri. It is reasonable to speculate that during speaking the IFG, or some portion of it, influences by corticocortical connections the orofacial representational area of primary motor cortex. To test the hypothesis that such corticocortical connections exist, electrical-stimulation tract tracing experiments were performed intraoperatively on 14 human subjects undergoing surgical treatment of medically intractable epilepsy. Bipolar electrical stimulation was applied to sites on the IFG, while the resulting evoked potentials were recorded from orofacial motor cortex, using a multichannel recording array. Stimulation of the IFG evoked polyphasic waveforms on motor cortex of both language-dominant and -nondominant hemispheres. The evoked waveforms had consistent features across subjects. The responses were seen in discrete regions on precentral cortex. Stimulation of motor cortex also evoked responses on portions of IFG. The data provide evidence for a functional connection between the human IFG and orofacial motor cortex.

Viewing the motion of human body parts activates different regions of premotor, temporal, and parietal cortex

Activation of premotor and temporoparietal cortex occurs when we observe others movements, particularly relating to objects. Viewing the motion of different body parts without the context of an object has not been systematically evaluated. During a 3T fMRI study, 12 healthy subjects viewed human face, hand, and leg motion, which was not directed at or did not involve an object. Activation was identified relative to static images of the same human face, hand, and leg in both individual subject and group average data. Four clear activation foci emerged: (1) right MT/V5 activated to all forms of viewed motion; (2) right STS activated to face and leg motion; (3) ventral premotor cortex activated to face, hand, and leg motion in the right hemisphere and to leg motion in the left hemisphere; and (4) anterior intraparietal cortex (aIP) was active bilaterally to viewing hand motion and in the right hemisphere leg motion. In addition, in the group data, a somatotopic activation pattern for viewing face, hand, and leg motion occurred in right ventral premotor cortex. Activation patterns in STS and aIP were more complex--typically activation foci to viewing two types of human motion showed some overlap. Activation in individual subjects was similar; however, activation to hand motion also occurred in the STS with a variable location across subjects--explaining the lack of a clear activation focus in the group data. The data indicate that there are selective responses to viewing motion of different body parts in the human brain that are independent of object or tool use.

Cytoarchitecture and cortical connections of the posterior cingulate and adjacent somatosensory fields in the rhesus monkey

The cytoarchitecture and connections of the caudal cingulate and medial somatosensory areas were investigated in the rhesus monkey. There is a stepwise laminar differentiation starting from retrosplenial area 30 towards the isocortical regions of the medial parietal cortex. This includes a gradational emphasis on supragranular laminar organization and general reduction of the infragranular neurons as one proceeds from area 30 toward the medial parietal regions, including areas 3, 1, 2, 5, 31, and the supplementary sensory area (SSA). This trend includes a progressive increase in layer IV neurons. Area 23c in the lower bank and transitional somatosensory area (TSA) in the upper bank of the cingulate sulcus appear as nodal points. From area 23c and TSA the architectonic progression can be traced in three directions: one culminates in areas 3a and 3b (core line), the second in areas 1, 2, and 5 (belt line), and the third in areas 31 and SSA (root line). These architectonic gradients are reflected in the connections of these regions. Thus, cingulate areas (30, 23a, and 23b) are connected with area 23c and TSA on the one hand and have widespread connections with parieto-temporal, frontal, and parahippocampal (limbic) regions on the other. Area 23c has connections with areas 30, 23a and b, and TSA as well as with medial somatosensory areas 3, 1, 2, 5, and SSA. Area 23c also has connections with parietotemporal, frontal, and limbic areas similar to areas 30, 23a, and 23b. Area TSA, like area 23c, has connections with areas 3, 1, 2, 5, and SSA. However, it has only limited connections with the parietotemporal and frontal regions and none with the parahippocampal gyrus. Medial area 3 is mainly connected to medial and dorsal sensory areas 3, 1, 2, 5, and SSA and to areas 4 and 6 as well as to supplementary (M2 or area 6m), rostral cingulate (M3 or areas 24c and d), and caudal cingulate (M4 or areas 23c and d) motor cortices. Thus, in parallel with the architectonic gradient of laminar differentiation, there is also a progressive shift in the pattern of corticocortical connections. Cingulate areas have widespread connections with limbic, parietotemporal, and frontal association areas, whereas parietal area 3 has more restricted connections with adjacent somatosensory and motor cortices. TSA is primarily related to the somatosensory-motor areas and has limited connections with the parietotemporal and frontal association cortices.

Input–output organization of the rostral part of the dorsal premotor cortex, with special reference to its corticostriatal projection

Until recently, little was known about the rostral part of the dorsal premotor cortex (PMdr). In the present study, somatotopical representations of the PMdr were electrophysiologically identified in the macaque monkey, and the distribution of corticostriatal input from the forelimb region of the PMdr was analyzed in relation to its thalamocortical and intracortical (with the frontal lobe) connections. Results have revealed that (1) the forelimb is represented predominantly in the PMdr, while only a few sites representing other body parts are distributed as embedded within the forelimb representation; (2) the corticostriatal input zone is located in the striatal cell bridges and their surroundings; (3) the cells of origin of the thalamocortical projections to the PMdr are located mainly in the parvicellular division of the ventroanterior nucleus, the oral divison of the ventrolateral nucleus, area X, the caudal divison of the ventrolateral nucleus, the mediodorsal nucleus, and the intralaminar nuclear group; (4) the PMdr is interconnected primarily with higher-order motor-related areas and dorsal area 46. These data indicate that the input-output pattern of the PMdr resembles those of the presupplementary motor area and the rostral cingulate motor area, and that the PMdr may play critical roles in higher-order motor functions.

Cortical Orofacial Motor Representation in Old World Monkeys, Great Apes, and Humans

This study presents a comparative stereologic investigation of neurofilament protein- and calcium-binding protein-immunoreactive neurons within the region of orofacial representation of primary motor cortex (Brodmann's area 4) in several catarrhine primate species (Macaca fascicularis, Papio anubis, Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Homo sapiens). Results showed that the density of interneurons involved in vertical interlaminar processing (i.e., calbindin- and calretinin-immunoreactive neurons) as well pyramidal neurons that supply heavily-myelinated projections (i.e., neurofilament protein-immunoreactive neurons) are correlated with overall neuronal density, whereas interneurons making transcolumnar connections (i.e., parvalbumin-immunoreactive neurons) do not exhibit such a relationship. These results suggest that differential scaling rules apply to different neuronal subtypes depending on their functional role in cortical circuitry. For example, cortical columns across catarrhine species appear to involve a similar conserved network of intracolumnar inhibitory interconnections, as represented by the distribution of calbindin- and calretinin-immunoreactive neurons. The subpopulation of horizontally-oriented wide-arbor interneurons, on the other hand, increases in density relative to other interneuron subpopulations in large brains. Due to these scaling trends, the region of orofacial representation of primary motor cortex in great apes and humans is characterized by a greater proportion of neurons enriched in neurofilament protein and parvalbumin compared to the Old World monkeys examined. These modifications might contribute to the voluntary dexterous control of orofacial muscles in great ape and human communication.

Cortical orofacial motor representation in Old World monkeys, great apes, and humans. I. Quantitative analysis of cytoarchitecture

Social life in anthropoid primates is mediated by interindividual communication, involving movements of the orofacial muscles for the production of vocalization and gestural expression. Although phylogenetic diversity has been reported in the auditory and visual communication systems of primates, little is known about the comparative neuroanatomy that subserves orofacial movement. The current study reports results from quantitative image analysis of the region corresponding to orofacial representation of primary motor cortex (Brodmann's area 4) in several catarrhine primate species (Macaca fascicularis, Papio anubis, Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Homo sapiens) using the Grey Level Index method. This cortical region has been implicated in the execution of skilled motor activities such as voluntary facial expression and human speech. Density profiles of the laminar distribution of Nissl-stained neuronal somata were acquired from high-resolution images to quantify cytoarchitectural patterns. Despite general similarity in these profiles across catarrhines, multivariate analysis showed that cytoarchitectural patterns of individuals were more similar within-species versus between-species. Compared to Old World monkeys, the orofacial representation of area 4 in great apes and humans was characterized by an increased relative thickness of layer III and overall lower cell volume densities, providing more neuropil space for interconnections. These phylogenetic differences in microstructure might provide an anatomical substrate for the evolution of greater volitional fine motor control of facial expressions in great apes and humans.

Thalamocortical and intracortical connections of monkey cingulate motor areas

Although there has been an increasing interest in motor functions of the cingulate motor areas, data concerning their input organization are still limited. To address this issue, the patterns of thalamic and cortical inputs to the rostral (CMAr), dorsal (CMAd), and ventral (CMAv) cingulate motor areas were investigated in the macaque monkey. Tracer injections were made into identified forelimb representations of these areas, and the distributions of retrogradely labeled neurons were analyzed in the thalamus and the frontal cortex. The cells of origin of thalamocortical projections to the CMAr were located mainly in the parvicellular division of the ventroanterior nucleus and the oral division of the ventrolateral nucleus (VLo). On the other hand, the thalamocortical neurons to the CMAd/CMAv were distributed predominantly in the VLo and the oral division of the ventroposterolateral nucleus-the caudal division of the ventrolateral nucleus. Additionally, many neurons in the intralaminar nuclear group were seen to project to the cingulate motor areas. Except for their well-developed interconnections, the corticocortical projections to the CMAr and CMAd/CMAv were also distinctively preferential. Major inputs to the CMAr arose from the presupplementary motor area and the dorsal premotor cortex, whereas inputs to the CMAd/CMAv originated not only from these areas but also from the supplementary motor area and the primary motor cortex. The present results indicate that the CMAr and the caudal cingulate motor area (involving both the CMAd and the CMAv) are characterized by distinct patterns of thalamocortical and intracortical connections, reflecting their functional differences.

Why are smiles contagious? An fMRI study of the interaction between perception of facial affect and facial movements

In human communication there is often a close relationship between the perception of an emotionally expressive face and the facial response of the viewer himself. Whereas perception and generation of facial expressions have been studied separately with functional imaging methods, no studies exist on their interaction. We combined the presentation of emotionally expressive faces with the instruction to react with facial movements predetermined and assigned. fMRI was used in an event related design to examine healthy subjects while they regarded happy, sad, or neutral faces and were instructed to simultaneously move the corners of their mouths either (a). upwards or (b). downwards, or (c). to refrain from movement. The subjects' facial movements were recorded with an MR-compatible video camera. Movement latencies were shortened in congruent situations (e.g. the presentation of a happy face and combined with upward movements) and delayed in non-congruent situations. Dissonant more than congruent stimuli activated the inferior prefrontal cortex and the somatomotor cortex bilaterally. The congruent condition, in particular when seeing a happy face, activated the medial basotemporal lobes (hippocampus, amygdala, parahippocampal region). We hypothesize that this region facilitates congruent facial movements when an emotionally expressive face is perceived and that it is part of a system for non-volitional emotional facial movements.

Neural activity in monkey dorsal and ventral cingulate motor areas: comparison with the supplementary motor area

The cingulate motor areas are a recently discovered group of discrete cortical regions located in the cingulate sulcus with direct connections to the primary motor cortex and spinal cord. Although much is known about their anatomical relationship with other motor areas, relatively little is known about their functional neurophysiology. We investigated neural mechanisms of motor processing in the dorsal and ventral cingulate motor areas (CMAd and CMAv) during two-dimensional visually guided arm movements. Single-neuron activity in CMAd and CMAv was recorded during an instructed delay task requiring combined elbow and shoulder movements. Neural activity associated with the onset of a visual cue (signal activity), delay (set activity), and motor response (movement activity) were assessed, and their onset time, duration, magnitude, and parameters of directional specificity were calculated. To determine how CMAd and CMAv compared with other premotor areas, we also analyzed the activity of neurons in the supplementary motor area (SMA) during the same task in the same monkeys. Comparison of CMAd, CMAv, and SMA revealed remarkably similar response properties. All three areas contained signal, set, and movement activity in similar proportions and in all possible combinations within single neurons. The average onset time of signal and set activity and the duration of signal activity were not significantly different across areas. The directional tuning of activities in all three areas were uniformly distributed and highly correlated within the same neuron. There were, however, some notable differences in movement activity between motor areas. Neurons with only movement activity were more numerous in CMAd and CMAv, whereas neurons with both set and movement activity were more prevalent in SMA. Furthermore, movement activity in SMA began earlier and had a shorter duration than movement activity in CMAd and CMAv, although there was substantial overlap in their distributions. These results indicate that CMAd and CMAv participate in the visual guidance of limb movements using similar neurophysiological mechanisms as SMA. The earlier average onset and shorter duration of movement activity in SMA suggest a more prominent role for this area in movement initiation, whereas the later onset and longer duration of movement activity in CMAd and CMAv suggest a more influential role in movement execution. Notwithstanding these differences, however, the remarkable similarities in response types and their combinatorial organization within single neurons across all cortical areas attests to the parallel organization and distributed nature of information processing in these three motor areas.

Differential processing patterns of motor information via striatopallidal and striatonigral projections

The functional loop linking the frontal lobe and the basal ganglia plays an important role in the control of motor behaviors. To delineate the principal features of motor information processing in the cortico-basal ganglia loop, the present study aimed at investigating how corticostriatal inputs from the primary motor cortex (MI) and the supplementary motor area (SMA) are transposed onto the pallidal complex and the substantia nigra. In macaque monkeys, stimulating electrodes were chronically implanted into identified forelimb representations of the MI and SMA. Subsequently, the distribution of neurons exhibiting orthodromic responses was examined in the caudal putamen to demarcate striatal zones receiving inputs separately or confluently from the MI and SMA. Finally, anterograde double labeling was performed by paired injections of tracers into two of three identified zones: the MI-recipient zone, SMA-recipient zone, and the convergent zone. Data have revealed that inputs from the MI-recipient and SMA-recipient striatal zones were substantially segregated in the pallidal complex and that those from the convergent zone were distributed to fill in blanks made by terminal bands derived from the MI and SMA. On the other hand, striatonigral inputs from the SMA-recipient and convergent zones of the putamen largely overlapped, while the input from the MI-recipient zone was minimal. The present results clearly indicate that the mode to process corticostriatal motor information through the striatopallidal and striatonigral projections is target-dependent, such that the parallel versus convergent rules govern the arrangement of striatopallidal or striatonigral inputs, respectively.

Localization of arm representation in the corona radiata and internal capsule in the non-human primate

Localization of the corticofugal projection in the corona radiata (CR) and internal capsule (IC) can assist in evaluating a patient's residual motor capacity following subtotal brain damage and predicting their potential for functional restitution. To advance our understanding of the organization of the corticofugal projection in this critical brain region, we studied the trajectories of the projection arising from six different cortical arm representations in rhesus monkeys. They included the arm representation of the primary (M1), ventral lateral pre- (LPMCv), dorsolateral pre- (LPMCd), supplementary (M2), rostral cingulate (M3) and caudal cingulate (M4) motor cortices. In the CR, each pathway was segregated as medial motor area fibres arched over the caudate and lateral motor area fibres arched over the putamen. In the IC, the individual corticofugal pathways were found to be widespread, topographically organized and partially overlapping. At superior levels of the IC, the corticofugal projection from the arm representation of M3 coursed through the middle and posterior portion of the anterior limb (ICa). The projection from M2 passed through the posterior portion of the ICa and the genu (ICg). The projection from LPMCv travelled through the genu and anterior portion of the posterior limb (ICp). The projection from LPMCd occupied the anterior portion of the ICp. The projection from M4 descended through the mid-portion of the ICp. Fibres from M1 also travelled in the ICp, positioned immediately posterior to the M4 projection. As each fibre system progressed inferiorly within the IC, all fibres shifted posteriorly to occupy the ICp. Within the ICp, the projections from M3, M2, LPMCv, LPMCd, M4 and M1 maintained their anterior to posterior orientation, respectively. M2, LPMCd and LPMCv fibres overlapped extensively, as did fibres from M4 and M1. Our data suggest that CR and superior capsular lesions may correlate with more favourable levels of functional recovery due to the widespread nature of arm representation. In contrast, the extensive overlap and comparatively condensed organization of arm representation at inferior capsular levels suggest that lesions seated inferiorly are likely to correlate with poorer levels of recovery of upper limb movement. Based on the relative density of corticospinal neurones associated with the motor areas studied, our findings also suggest that motor deficit severity is likely to increase as a lesion occupies progressively more posterior regions of the IC.