Multiple Motor Areas Research Articles

Cytoarchitecture of sensorimotor areas in the cat cerebral cortex.

The organization of multiple motor areas in the cerebral cortex has been investigated frequently in primates but rarely in nonprimate species. To compare sensorimotor areas in cats and primates, the cytoarchitecture of frontal and parietal areas of the cat cerebral cortex was described and mapped from coronal sections stained with cresyl violet or thionine. Multiple subdivisions of areas 4 and 6 were recognized; of these, the cytoarchitecture of area 4 gamma is similar to that of area 4 described in other carnivores and in primates and is characterized by giant pyramidal cells in multiple rows or clusters in lamina V. In other subdivisions of area 4 (4 delta, 4sfu, and 4fu), giant pyramidal cells are few or absent in lamina V, and these subdivisions resemble area 6 of primates. Area 6 of the cat cortex is heterogeneous, and differences in laminar appearance and size of pyramidal cells in lamina V distinguish its four subdivisions (6a alpha, 6a beta, 6a gamma, and 6iffu). The adjoining prefrontal areas are distinguishable from area 6 by the presence of a thin internal granular lamina (lamina IV) and the reduced size of pyramidal cells in lamina V. Laminae are poorly differentiated in the cingulate areas, where a rostral and caudal subdivision can be distinguished on the basis of the absence or presence of lamina IV. Area 3a is characterized by a thin lamina IV and is located between frontal agranular and parietal granular (well-defined lamina IV) fields (3b, 1, 2, 2pri, 5, and 7). Insular cortex can be subdivided into granular and agranular fields.

Multiple Nonprimary Motor Areas in the Human Cortex

We measured the distribution of regional cerebral blood flow with positron emission tomography while three subjects moved their hand, shoulder, or leg. The images were coregistered with each individual's anatomic magnetic resonance scans. The data were analyzed for each individual to avoid intersubject averaging and so to preserve individual gyral anatomy. Instead of inspecting all pixels, we prospectively restricted the data analysis to particular areas of interest. These were defined on basis of the anatomic and physiological literature on nonhuman primates. By examining only a subset of areas, we strengthened the power of the statistical analysis and thereby increased the confidence in reporting single subject data. On the lateral convexity, motor related activity was found for all three subjects in the primary motor cortex, lateral premotor cortex, and an opercular area within the premotor cortex. In addition, there was activation of somatosensory cortex (SI), the supplementary somatosensory area (SII) in the Sylvian fissure, and parietal association areas (Brodmann areas 5 and 40). There was also activation in the insula. We suggest that the activation in the dorsal premotor cortex may correspond with dorsal premotor area (PMd) as described in the macaque brain. We propose three hypotheses as to the probable location of vental premotor area (PMv) in the human brain. On the medial surface, motor-related activity was found for all three subjects in the leg areas of the primary motor cortex and somatosensory cortex and also activity for the hand, shoulder, and leg in the supplementary motor area (SMA) on the dorsal medial convexity and in three areas in the cingulate sulcus. We suggest that the three cingulate areas may correspond with rostral cingulate premotor area, dorsal cingulate motor area (CMAd), and ventral cingulate motor area (CMAv) as identified in the macaque brain. Somatotopic mapping was demonstrated in the primary motor and primary somatosensory cortex. In all three subjects, the arm region lay anterior to the leg region in parietal area 5. Also in all three subjects, the arm region lay anterior to the leg region in the supplementary motor cortex.

An fMRI study of the human cortical motor system response to increasing functional demands

Functional magnetic resonance imaging (fMRI) was used to study activation changes in the human primary motor-sensory areas (MAs), supplementary motor areas (SMAs), premotor areas (PMAs) and the superior and inferior parietal areas (SPAs, IPAs) during right hand finger movements as the rate, force and complexity of movement were varied. A preliminary reproducibility study of a single subject doing the same repetitive index finger movements in nine different sessions over a six week period demonstrated highly consistent and highly localized activation in the contralateral MA. ANOVAs demonstrated highly significant main effects of increasing the force and complexity of movement, thereby illustrating the distributed and integrated systemic character of the cortical motor system. Interactions between brain region and the rate and complexity of movements suggested functional specialization of some components of the system. Increasing the rate of movement led to increased activity only in the contralateral MA; increasing complexity led to greater increases in activity in the left and right SPAs and the left IPA than in other areas. Although activation was evident in varying degree throughout the multiple motor areas, only the MAs showed consistent lateralization of activation.

Multiple cortical motor areas and temporal sequencing of movements

Multiple cortical motor areas and temporal sequencing of movements

Neurochemical, morphologic, and laminar characterization of cortical projection neurons in the cingulate motor areas of the macaque monkey.

The primate cingulate gyrus contains multiple cortical areas that can be distinguished by several neurochemical features, including the distribution of neurofilament protein-enriched pyramidal neurons. In addition, connectivity and functional properties indicate that there are multiple motor areas in the cortex lining the cingulate sulcus. These motor areas were targeted for analysis of potential interactions among regional specialization, connectivity, and cellular characteristics such as neurochemical profile and morphology. Specifically, intracortical injections of retrogradely transported dyes and intracellular injection were combined with immunocytochemistry to investigate neurons projecting from the cingulate motor areas to the putative forelimb region of the primary motor cortex, area M1. Two separate groups of neurons projecting to area M1 emanated from the cingulate sulcus, one anterior and one posterior, both of which furnished commissural and ipsilateral connections with area M1. The primary difference between the two populations was laminar origin, with the anterior projection originating largely in deep layers, and the posterior projection taking origin equally in superficial and deep layers. With regard to cellular morphology, the anterior projection exhibited more morphologic diversity than the posterior projection. Commissural projections from both anterior and posterior fields originated largely in layer VI. Neurofilament protein distribution was a reliable tool for localizing the two projections and for discriminating between them. Comparable proportions of the two sets of projection neurons contained neurofilament protein, although the density and distribution of the total population of neurofilament protein-enriched neurons was very different in the two subareas of origin. Within a projection, the participating neurons exhibited a high degree of morphologic heterogeneity, and no correlation was observed between somatodendritic morphology and neurofilament protein content. Thus, although the neurons that provide the anterior and posterior cingulate motor projections to area M1 differ morphologically and in laminar origin, their neurochemical profiles are similar with respect to neurofilament protein. This suggests that neurochemical phenotype may be a more important unifying feature for corticocortical projections than morphology.

Recovery from Motor Stroke: Human Positron Emission Tomography Studies

Three major studies have investigated the reorganisation of the human motor system after stroke by measuring changes in regional cerebral blood flow during defined tasks with positron emission tomography. The results imply that there is considerable scope for functional plasticity in the adult human brain. Changes in both the damaged and the undamaged hemisphere can be observed. The pattern of reorganisation differs in individual patients, depending on the location of the lesion. While substitution of function in homologous brain regions of the undamaged hemisphere may occur in some patients, redistribution of activity within a widespread network of parallel-acting multiple motor areas and pathways constitutes the central mechanism in motor recovery.

Parceling of mesial frontal motor areas during ideation and movement using functional magnetic resonance imaging at 1.5 tesla.

Finger movement-related responses were identified in three discrete sites of mesial frontal cortex in 7 normal subjects using high resolution functional magnetic resonance imaging. During imagination of the same movements there was a differential response with rostral areas more active than caudal areas. Humans have multiple motor areas in mesial frontal cortex that subserve different functions in motor planning and execution.

Within-arm somatotopy in human motor areas determined by positron emission tomography imaging of cerebral blood flow.

Within-arm somatotopy was identified in multiple motor areas of six normal human subjects who performed a visuomotor tracking task during positron emission tomography (PET) measurement of relative cerebral blood flow (relCBF). A randomly moving target, presented on a computer monitor, was continuously followed with the index finger (movement at the metacarpophalangeal joint), thumb, fist (movement at the wrist), forearm (movement at the elbow), elbow (movement at the shoulder), and eyes alone (control task) during sequential imaging. Segmental limb movements were associated with relCBF responses in the contralateral motor, supplementary motor, cingulate, and parietal cortex, and in the ipsilateral cerebellum. Localization of responses after stereotaxic transformation into Talairach atlas space, as well as within-subject analysis without anatomic deformations, demonstrated an overlapping somatotopic distribution in the motor cortex, with thumb responses most ventrolateral and shoulder responses most dorsomedial. Proximal limb movements induced relCBF responses of greater magnitude than distal movements. Somatotopy was also identified in the supplementary motor area, with index finger responses dorsal and anterior to shoulder responses. An additional set of somatotopic responses were located in the cingulate cortex, also with finger responses anterior to shoulder responses. Somatotopy was not identified in the anterior cerebellum. The distribution of relCBF responses is concordant with electrophysiologic studies in nonhuman primates that demonstrate a fractured somatotopy on a fine scale and a general somatotopic scheme of the limb on a large scale in multiple discrete motor areas.

Multiple Output Channels in the Basal Ganglia

The neural circuits that link the basal ganglia with the cerebral cortex are critically involved in the generation and control of voluntary movement. Retrograde transneuronal transport of herpes simplex virus type 1 was used to examine the organization of connections in the cebus monkey between an output nucleus of the basal ganglia, the internal segment of the globus pallidus (GPi), and three cortical areas: the primary motor cortex, the supplementary motor ara, and the ventral premotor area. Spatially separate regions of the GPi were labeled after virus injections into each cortical area. The GPi projects to multiple cortical motor areas, and this pallidal output is organized into discrete channels. This information provides a new anatomical framework for examining the function of the basal ganglia in skeletomotor control.

A hypothesis on the primate neocortex evolution: column-multiplication hypothesis.

A hypothesis is proposed, that the primate neocortex has evolved by the multiplication of cortical columns. As the column size is similar across primate species, it is considered that the columns have multiplied to expand the neocortex during primate evolution. This hypothesis would explain the expansion of neocortical sensory-motor-associational areas and multiple sensory and motor areas which had occurred during evolution. Further, the hypothesis predicts the existence of columns neutral for the fitness, genetic control upon the columns, and intraspecies variations of the columns.