Brodmann Areas – Part 1: Primary Somatosensory Cortex – A Brief Literature Review

Sensory Homunculus, Btarski, Creative Commons 3.0 License

Looking more closely at the Primary Somatosensory Cortex (PSC) in an effort to characterise the properties of the Brodmann Areas, i’m starting with an overview of the PSC with reference  to a variety of research papers highlighting the results of different research approaches. The PSC comprises Brodmann Areas 1, 2 and 3. The diagram above illustrates the results of the classic Penfield studies in which the Canadian Neurosurgeon identified through surface electrode stimulation the sensory correlate of each point on the cortical surface. For the PSC there was a distorted body map with an exaggerated representation of the lips and hands. Whilst Penfield’s original findings have been supported by subsequent research more recent studies have characterised the PCS as a dynamic structure in which maps are continuously reorganised and in which subtly variations of these maps are represented in other parts of the cortex.

The authors of this review article suggest that the face region of the PSC is involved in the integration of sensory and motor data in semi-automatic and voluntary orofacial movements and also in pathological disorders involving these movements. The authors of this review suggest three types of body schema – the somatosensory representations characteristic of the PSC, a secondary representation with body size and shape and third representation with kinaesthetic and tactile stimuli leading to postural maps. The authors of this review paper suggest that the somatosensory cortex is organised into micro and macrocolumns which compete with each other to more accurately represent sensory stimuli, features characteristic of neural network architectures. Differences between Brodmann Area 3 in humans and other apes were found in this post-mortem study which also characterised some of the important difference in other areas between species. An fMRI study in 10 subjects finds that there is a consistent representation for the little finger but not the index finger suggesting that maps for the two fingers develop differently. This fMRI study correlated greater contralateral PSC activation with active rather than passive touch. In other words where the hand moves over a stimulus rather than the stimulus moving under the hand. In this fMRI study, painful muscle stimulation activated brain regions associated with emotions (e.g Amygdala) in contrast with painful skin stimulation which activated contralateral PSC.

In a study of 20 people with traumatic peripheral nerve injury, nerve blockade reversed the pain. Magnetoencephalography was used to identify the corresponding cortical activation changes and the PSC was identified as the most likely correlate of this change in cortical activity. This supports the hypothesis that chronic pain is associated with reorganisation of the PCS. The authors of this review paper however suggest there is no abnormal processing of somatosensory stimuli in the facial area of the PCS. In one study, Transcranial Magnetic Stimulation over the contralateral PCS results in altered sensory perception in people with Parkinson’s Disease treated with dopaminergic therapy compared to controls. The researchers suggest that dopamine may be associated with sensory symptoms in Parkinson’s Disease. In a small PET study (n=15) recovery in hemiplegic stroke was associated with increased activity in the contralateral PSC compared to controls. In orofacial dystonia there was found to be an asymmetric somatosensory body map in this fMRI study. The authors of this review paper find that evoked responses in the PSC are modified by Migraines with or without aura.  Increased somatosensory evoked potentials are identified in Rett Syndrome but are probably secondary to widespread cortical hyperexcitability.

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

Area 6 (Agranular Frontal Area 6)

FDG-PET, Frontal Dysfunction and Mild Cognitive Impairment

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

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

Review: The Anterior Temporal Lobes and Semantic Memory

Area 27 (Piriform Cortex)

Anosmia in Lewy Body Dementia

Area 28  (Entorhinal Cortex)

MRI Measures of Temporoparietal Atrophy During Prodromal Alzheimer Disease*

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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