Philippe A. Chouinard

The Primary Motor and Premotor Areas of the Human Cerebral Cortex

Brodmanns cytoarchitectonic map of the human cortex designates area 4 as cortex in the anterior bank of the precentral sulcus and area 6 as cortex encompassing the precentral gyrus and the posterior portion of the superior frontal gyrus on both the lateral and medial surfaces of the brain. More than 70 years ago, Fulton proposed a functional distinction between these two areas, coining the terms primary motor areafor cortex in Brodmann area 4 and premotor areafor cortex in Brodmann area 6. The parcellation of the cortical motor system has subsequently become more complex. Several nonprimary motor areas have been identified in the brain of the macaque monkey, and associations between anatomy and function in the human brain are being tested continuously using brain mapping techniques. In the present review, the authors discuss the unique properties of the primary motor area (M1), the dorsal portion of the premotor cortex (PMd), and the ventral portion of the premotor cortex (PMv). They end this review by discussing how the premotor areas influence M1.

Role of the Primary Motor and Dorsal Premotor Cortices in the Anticipation of Forces during Object Lifting

When lifting small objects, people apply forces that match the expected weight of the object. This expectation relies in part on information acquired during a previous lift and on associating a certain weight with a particular object. Our study examined the role of the primary motor and dorsal premotor cortices in predicting weight based either on information acquired during a previous lift (no-cue experiment) or on arbitrary color cues associated with a particular weight (cue experiment). In the two experiments, subjects used precision grip to lift two different weights in a series of trials both before and after we applied low-frequency repetitive transcranial magnetic stimulation over the primary motor and dorsal premotor cortices. In the no-cue experiment, subjects did not receive any previous information about which of two weights they would have to lift. In the cue experiment, a color cue provided information about which of the two weights subjects would have to lift. Our results demonstrate a double dissociation in the effects induced by repetitive stimulation. When applied over the primary motor cortex, repetitive stimulation disrupted the scaling of forces based on information acquired during a previous lift. In contrast, when applied over the dorsal premotor cortex, repetitive stimulation disrupted the scaling of forces based on arbitrary color cues. We conclude that the primary motor and dorsal premotor cortices have unique roles during the anticipatory scaling of forces associated with the lifting of different weights.

Mechanisms of action underlying the effect of repetitive transcranial magnetic stimulation on mood: behavioral and brain imaging studies.

In a set of experiments, we applied 10-Hz repetitive transcranial magnetic stimulation (rTMS) over the left mid-dorsolateral frontal cortex (MDLFC) to investigate rTMS-induced changes in affective state and neural activity in healthy volunteers. In Experiment 1, we combined 10-Hz rTMS with a speech task to examine rTMS-induced changes in paralinguistic aspects of speech production, an affect-relevant behavior strongly linked to the ACC. In Experiment 2, we combined 10-Hz rTMS with positron emission tomography (PET) and used partial least squares (PLS) to identify a pattern of brain regions whose connectivity with the site of stimulation varied as a function of rTMS. The results of Experiment 1 revealed that following stimulation of the left MDLFC, subjects reported having less positive affect and vitality and displayed more monotonous speech. In Experiment 2, results revealed that 10-Hz rTMS influenced the covariation between blood flow at the site of stimulation (ie the left MDLFC) and blood flow in a number of affect-relevant brain regions including the perigenual anterior cingulate gyrus, insula, thalamus, parahippocampal gyrus, and caudate nucleus. Taken together, our results suggest that changes in affect and affect-relevant behaviour following 10-Hz rTMS applied over the left MDLFC may be related to changes in neural activity in brain regions widely implicated in affective states, including a frontocingulate circuit.

Retinotopic activity in V1 reflects the perceived and not the retinal size of an afterimage

An afterimage looks larger when one fixates on a distant than on a closer surface. We show that the retinotopic activity in the primary visual cortex (V1) associated with viewing an afterimage is modulated by perceived size, even when the size of the retinal image remains constant. This suggests that V1 has an important role in size constancy when the viewing distance of the stimulus changes.

Dissociable neural mechanisms for determining the perceived heaviness of objects and the predicted weight of objects during lifting: An fMRI investigation of the size-weight illusion

In size-weight (SW) illusions, people learn to scale their fingertip forces for lifting small and big objects of equal weight even though they fail to learn perceptually that both objects have the same weight. The question then arises as to what the separate neural mechanisms are for determining the perceived heaviness of objects and the predicted weight of these objects during lifting. To answer this question, we used fMRI to first identify areas that code for the size, weight, and density of objects using an adaptation paradigm. We then contrasted BOLD in the SW illusion condition in which subjects falsely perceived the smaller of two equally weighted objects as heavier versus a condition in which size and weight did not differ between objects. Sensory areas in the parietal and temporal cortex adapted to the size of objects and the primary motor area (M1) contralateral to the lifting hand adapted to the weight of objects. The ventral premotor area (PMv), which did not adapt to either the size or the weight of objects, adapted instead to the density of objects, and responded more when subjects falsely perceived differences in weight between objects in the SW illusion condition. Taken together, we conclude that the real-world properties of objects, such as size and weight, are computed by sensory areas and by M1 respectively, whereas the perceived heaviness of objects, presumably based on their apparent density, is computed by PMv, a higher-order area well placed to integrate sensory information about the size of objects and the weight of objects.

Category-specific neural processing for naming pictures of animals and naming pictures of tools: An ALE meta-analysis

Using activation-likelihood estimation (ALE) meta-analysis, we identified brain areas that are invoked when people name pictures of animals and pictures of tools. We found that naming animals and naming tools invoked separate distributed networks in the brain. Specifically, we found that naming animals invoked greater responses than naming tools in frontal lobe structures that are typically modulated by emotional content and task demands, and in a number of visual areas in the ventral stream. In contrast, naming tools invoked greater responses in a different set of areas in the ventral stream than those invoked by naming animals. Naming tools also invoked greater responses than naming animals in motor areas in the frontal lobe as well as in sensory areas in the parietal lobe. The only overlapping sites of activation that we found for naming these two categories of objects were in the left pars triangularis, the left inferior temporal gyrus, and the left parahippocampal gyrus. Taken together, our meta-analysis reveals that animals and tools are categorically represented in visual areas but show convergence in higher-order associative areas in the temporal and frontal lobes in regions that are typically regarded as being involved in memory and/or semantic processing. Our results also reveal that naming tools not only engages visual areas in the ventral stream but also a fronto-parietal network associated with tool use. Whether or not this network associated with tool use contributes directly to recognition will require further investigation.

Changes in effective connectivity of the primary motor cortex in stroke patients after rehabilitative therapy.

We used a perturb-and-measure approach, by combining transcranial magnetic stimulation (TMS) and positron emission tomography (PET), to examine changes in the primary motor area (M1) and its effective connectivity in stroke patients with chronic motor deficits (>1-year post-stroke) who underwent 3 weeks of constraint-induced movement therapy. During the 3-week period, 7 patients spent 4 h per day performing shaping exercises with the affected arm under our supervision for 14 days and wore a mitt on the unaffected arm at home in situations where safety was not compromised. Anatomical magnetic resonance imaging confirmed that all patients had lesions that encompassed the white matter; no patient had damage in the hand representation of M1. Improvements on various motor tests were observed immediately after therapy and 1 month afterwards. During the TMS/PET sessions, we applied trains of subthreshold 10-Hz repetitive TMS over the hand representation of the ipsilesional and contralesional M1s and varied the number of TMS trains delivered during each scan. The results demonstrate changes in the local response of TMS in the ipsilesional and contralesional M1, changes in the strength of interhemispheric connectivity between M1s, and changes in the effective connectivity of the ipsilesional and contralesional M1s with the non-primary motor areas, the basal ganglia, and the motor nuclei of the thalamus.

What have We Learned from "Perturbing" the Human Cortical Motor System with Transcranial Magnetic Stimulation?

The purpose of this paper is twofold. First, we will review different approaches that one can use with transcranial magnetic stimulation (TMS) to study both its effects on motor behavior and on neural connections in the human brain. Second, we will present evidence obtained in TMS-based studies showing that the dorsal premotor area (PMd), the ventral premotor area (PMv), the supplementary motor area (SMA), and the pre-supplementary motor area (pre-SMA) each have different roles to play in motor behavior. We highlight the importance of the PMd in response selection based on arbitrary cues and in the control of arm movements, the PMv in grasping and in the discrimination of bodily actions, the SMA in movement sequencing and in bimanual coordination, and the pre-SMA in cognitive control. We will also discuss ways in which TMS can be used to chart “true” cerebral reorganization in clinical populations and how TMS might be used as a therapeutic tool to facilitate motor recovery after stroke. We will end our review by discussing some of the methodological challenges and future directions for using this tool in basic and clinical neuroscience.

Repetition suppression in occipital-temporal visual areas is modulated by physical rather than semantic features of objects.

Functional magnetic-resonance imaging was used to identify areas involved in naming objects and to examine which of these areas adapted to either physical or semantics features of objects. We presented successive pairs of objects that were either the same exemplar of an object, different exemplars of that object, or different objects. By controlling for differences in physical features between pairs of different exemplars and different objects, visual areas in the occipital-temporal cortex were subject to repetition suppression when the same exemplars of an object were repeated, but not when different exemplars of an object were repeated. This was true independent of whether or not participants named objects. Repetition suppression in visual areas appeared therefore bound to physical features. Nevertheless, repetition suppression for physical features was greater in left visual areas when objects were named, suggesting that naming, known to depend on mechanisms in the left hemisphere, may induce greater attentional modulation in the left than in the right visual areas. Taken together, we propose that the difference between our findings and those of earlier studies that report semantic influences can be explained by the failure of those studies to control for differences in the appearance of different exemplars. Left frontal areas showed repetition suppression when either the same or different exemplars of an object were repeated, but only when participants named objects. These results suggest that visual areas process information about physical features without semantic modulation by higher-order areas, and that left frontal areas process semantic features, but the engagement of these processes is task modulated.

Global processing during the Müller‑Lyer illusion is distinctively affected by the degree of autistic traits in the typical population

Earlier work examining susceptibility to visual illusions in autism has reported discrepant findings. Some of this research suggests that global processing is affected in autism while some of this research suggests otherwise. The discrepancies may relate to compliance issues and differences in population samples in terms of symptom severity, cognitive ability, and co-morbid disorders. Equally important, most of this work tended to treat global processing as if it were a singular construct, invoking similar cognitive operations across different visual illusions. We argue that this is not a fair assumption to make given the extensive research that has classified visual illusions on the basis of their cognitive demands. With this in mind, and to overcome the many caveats associated with examining a heterogeneous disorder such as autism directly, we examined how susceptibility to various illusions relates differently to people’s scores on the Autism Spectrum Quotient (AQ) questionnaire. We found that susceptibility to the Müller-Lyer but not to the Ebbinghaus and Ponzo illusions decreased as a function of AQ and that the relationship between AQ and susceptibility to the Müller-Lyer illusion was different from those between AQ and susceptibility to the Ebbinghaus and Ponzo illusions. Our findings confirm that the cognitive operations underlying global processing in the Müller-Lyer illusion are different from the other illusions and, more importantly, reveal that they might be affected in autism. Future brain mapping studies could provide additional insight into the neural underpinnings of how global processing might and might not be affected in autism.