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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.
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Appendix – Articles Reviewed in relation to Brodmann Areas or other Structures
Brodmann Area 1 – Somatosensory Cortex
Brodmann Area 2 – The Primary Motor Cortex
Brodmann Area 6 (Agranular Frontal Area 6)
Brodmann Areas 13 and 14 (Insular Cortex)
Brodmann Area 15 (Anterior Temporal Lobe – Controversial Area in Humans)
Brodmann Area 27 (Piriform Cortex)
Brodmann Area 28 (Entorhinal Cortex)
Brodmann Areas 45, 46, 47 (Inferior Frontal Gyrus)
Medial Temporal Lobe
Miscellaneous Subcortical Structures
Generic Articles Relating to Localisation
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