Brodmann Areas – Part 2: Area 4. The Primary Motor Cortex – A Brief Literature Review

User:WashingtonIrving*, Ba4, Creative Commons 3.0

This is the second in a series on the Brodmann Areas. The subject of this review is Brodmann Area 4 otherwise known as the Primary Motor Cortex (PMC) and this consists of a brief overview of some of the papers in the literature providing the reader with a guide to further explore the subject. The relation of the PMC to skilled motor performance is discussed in this paper (available here). A 26-year old review of the role of cerebral cortex in voluntary movements is to be found in this paper (available here) which offers an interesting historical perspective for comparison with more recent papers. The PMC is used to examine the relationship between cortical plasticity and Transcranial Magnetic Stimulation (TMS) in this study presumably because the effects of stimulation of the primary motor cortex are relatively easy to measure. The paradigm of rTMS enhancing motor function is explored in this paper. Two renowned scientists detail the results of research utilising TMS in elucidating the properties of the PMC in relation to activity in the Ventral Premotor Cortex, Dorsal Premotor Cortex and Posterior Parietal Cortex in this paper. They conclude that the relationship is dynamic and influenced by a number of factors including the task and general  conditions under which the task is completed.

The PMC is a natural subject for study a number of motor disorders. In this paper, the author looks at recovery of motor function after stroke noting that there are several useful predictors of recovery including specific movements achieved within a certain timeframe as well as the results of diffusion-weighted imaging underaken with 7 days of the stroke.  The authors comments on possible future developments. The use of functional neuroimaging studies is examined in this systematic review where 869 studies are reduced to 22 which meet the inclusion criteria. The authors conclude that after stroke several trends emerge in the studies including ‘unilateral overactivation’ of motor areas as well as a ‘posterior shift in activity’ in the PMC. The use of motor imagery in post-stroke rehabilitation is explored in this paper where the authors mention in passing that the issue of whether the mechanism of action involves the PMC is still unresolved. Levodopa-induced dyskinesias were modified by right repetitive TMS of the PMC in this study and follows a consensus paper on the TMS for PMC stimulation in dystonia and levodopa-induced dyskinesia. Pathological changes in the Betz cells were associated with Corticobasal Degeneration in this case series of 10 post-mortems. The authors of this paper conclude that apraxia of speech with dysarthria is associated with damage in the left face area representation in the PMC compared to a control group with apraxia of speech alone.

The relationship of the PMC to pain is an interesting finding with a well developed literature. The authors of this paper suggest that distortions of the body map in the PMC may be associated with pain. The effect of stimulation of the PMC on intractable deafferentation pain is examined in this paper. The authors of this paper note that a number of studies have found evidence that repetitive TMS applied to the PMC modifies acute and chronic pain and comment on the potential for future research in this area.

There are a number of miscellaneous topics relating to the PMC. The characteristics of motor memory are discussed in this paper with reference both to the cerebellum and the PMC (paper available here). The visual and motor cortices are compared in this paper (available here). Characteristics of the sensorimotor cortex are reviewed in this paper. The existence of multiple facial maps and their relationship to facial expressions are examined in this review article while the author of this paper writes about the PMC being responsible for kinaesthetic perception of limb movements. Hand representation within the cortex including the PMC is the subject of this paper and a theory of handedness in humans relating to the PMC is postulated in this paper. The PMC is one of many areas activated during word reading as detailed by the authors of this paper (available here). Dopaminergic projections appear to be relatively understudied and are reviewed in this paper.

* User on Wikimedia Commons

Appendix – Articles Reviewed in relation to Brodmann Areas or other Structures

Brodmann Area 1 – Somatosensory Cortex

An Investigation of D3 Receptors and Brodmann Area 1 in Schizophrenia

YouTubing the Somatosensory Cortex

Brodmann Area 2 – The Primary Motor Cortex

YouTubing the Motor Cortex

Brodmann Area 6 (Agranular Frontal Area 6)

FDG-PET, Frontal Dysfunction and Mild Cognitive Impairment

Brodmann Areas 13 and 14 (Insular Cortex)

What does the Insular Cortex Do Again?

Insular Cortex Infarction in Acute Middle Cerebral Artery Territory Stroke

The Insular Cortex and Neuropsychiatric Disorders

Developing a Model of the Insular Cortex and Emotional Regulation Part 1

Developing a Model of the Insular Cortex: A Recap

The Relationship of Blood Pressure to Subcortical Lesions

Pathobiology of Visceral Pain

Interoception and the Insular Cortex

A Case of Neurogenic T-Wave Inversion

Video Presentations on a Model of the Insular Cortex

MR Visualisations of the Insula

The Subjective Experience of Pain*

How Do You Feel? Interoception: The Sense of the Physiological Condition of the Body

How Do You Feel – Now? The Anterior Insula and Human Awareness

Role of the Insular Cortex in the Modulation of Pain

The Insular Cortex and Frontotemporal Dementia

A Case of Infarct Connecting the Insular Cortex and the Heart

The Insular Cortex: Part of the Brain that Connects Smell and Taste?

Stuttered Swallowing and the Insular Cortex

Brodmann Area 15 (Anterior Temporal Lobe – Controversial Area in Humans)

Review: The Anterior Temporal Lobes and Semantic Memory

Brodmann Area 27 (Piriform Cortex)

Anosmia in Lewy Body Dementia

Brodmann Area 28  (Entorhinal Cortex)

MRI Measures of Temporoparietal Atrophy During Prodromal Alzheimer Disease*

Brodmann Areas 45, 46, 47 (Inferior Frontal Gyrus)

Which Bit of the Brain Detects the Emotions in Speech?

Medial Temporal Lobe

The Medial Temporal Lobe and Recognition Memory

Hippocampus

Review: Differences in Hippocampal Metabolism Between Amnestic and Non-Amnestic MCI Subjects

Anatomy of the Hippocampus

Review: Involvement of BDNF in Age-Dependent Alterations in the Hippocampus

Miscellaneous Subcortical Structures

Book Review: Subcortical Vascular Dementia

Review: Subcortical Vascular Ischaemic Dementia

Review: Psychiatric Disturbances in CADASIL

Review: Cognitive Decline in CADASIL

Review: Relationship Between 24-hour Blood Pressure, Subcortical Ischemic Lesions and Cognitive Impairment

Hypocretin and Neurological Disorders

A Case of Pontine and Extrapontine Myelinolysis with Catatonia

Generic Articles Relating to Localisation

A History of Human Brain Mapping

Book Review: Brain Architecture

Brain Folding and the Size of the Human Cerebral Cortex

An index of the site can be found here. The page contains links to all of the articles in the blog in chronological order. Twitter: You can follow ‘The Amazing World of Psychiatry’ Twitter by clicking on this link. Podcast: You can listen to this post on Odiogo by clicking on this link (there may be a small delay between publishing of the blog article and the availability of the podcast). It is available for a limited period. TAWOP Channel: You can follow the TAWOP Channel on YouTube by clicking on this link. Responses: If you have any comments, you can leave them below or alternatively e-mail justinmarley17@yahoo.co.uk. Disclaimer: The comments made here represent the opinions of the author and do not represent the profession or any body/organisation. The comments made here are not meant as a source of medical advice and those seeking medical advice are advised to consult with their own doctor. The author is not responsible for the contents of any external sites that are linked to in this blog.

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