Dr Korbinian Brodmann, German Neurologist, Frontpiece of ‘Localisation in the Cerebral Cortex’, 1909, Public Domain*
The Brain is a complex organ, responsible for the full gamete of our inner experiences whether these are our first thoughts on waking, the perception of a rainbow or the sharing of joy with others. Understanding the brain has been an almost unobtainable goal which many great scientists have striven for. One scientist who realised the immense complexity of the task set out to characterise the brain in a more limited way and in the process established one of the most successful maps of the brain which continues to be routinely used over 100 years later. His name was Dr Korbinian Brodmann. In the first part of this series, there was a brief look at the context of Brodmann’s landmark work ‘Brodmann’s Localisation in the Cerebral Cortex’. In the third part of the series we will take a closer look at the 21 pages of his book which relate to the special regions in the human Cerebral Cortex that Brodmann identified.
The central 21 pages of Brodmann’s work are contained within Chapter IV ‘Description of Individual Brain Maps’ in which he contrasts the brain maps of several species including humans. The second region he looks at is the Precentral region.
Cytoarchitectonics of human brain according to Brodmann (1909), Public Domain*
Three drawings by Santiago Ramon y Cajal, taken from the book “Comparative study of the sensory areas of the human cortex”, pages 314, 361, and 363, Public Domain*
Left: Nissl-stained visual cortex Middle: Nissl-stained motor cortex Right: Golgi-stained cortex
Medial surface of left cerebral hemisphere. Figure 727 from Gray’s Anatomy, Public Domain**
Brodmann divides the Precentral region into
1. Brodmann Area 4 – The Giant Pyramidal Area.
2. Brodmann Area 6 – The Agranular Frontal Area.
Both areas lacked an Inner Granular Layer – the fourth layer according to Meynert’s description of the Cerebral Cortex. The feature distinguishing between Areas 4 and 6 are the Betz cells. Brodmann states that the Precentral region extends past the Precentral Gyrus anteriorly as far as the Superior and Middle Frontal Gyri while posteriorly the Central Sulcus separates this region from Brodmann Area 3 (although there is individual variation in Central Sulcus depth of the demarcation).
Turning first to Brodmann Area 4, Brodmann describes this as passing along the Central Sulcus as well as being contained within the Precentral Gyrus and within part of the Paracentral Lobule. Brodmann also says that medially BA4 it is contained within the middle third of the Paracentral Lobule whilst laterally BA4 narrows on moving from Inferiorly (superiorly BA4 is described as occupying the width of the Precentral Gyrus). Brodmann describes a large individual variation in both the borders of BA4 and BA6 as well as the characteristics of the Betz cells. However he does state that the Betz cells decrease in size and number on moving inferiorly.
Regarding Brodmann Area 6, Brodmann states that BA4 could be classed as BA6 as it also lacks the Inner Granular Layer although as noted above, it lacks the Betz cells. BA6 like BA4 narrows inferiorly on the lateral Cortical surface. BA6 is contained within the frontal lobe region extending from the Sylvian fissure to the Callosomarginal Sulcus (now referred to as the Cingulate Sulcus). Brodmann identifies further details of BA6 according to the medial, lateral and inferior extent. Brodmann also challenges the subdivision of BA6 by his contemporary – Elliot Smith.
Brodmann’s Localisation in the Cerebral Cortex. 1909. Translated and Edited by Laurence J Garey. Springer. 2006.
*Public Domain in those countries where the Copyright term of the life of the author (Korbinian Brodmann 1868-1918) plus the additional country specific term has lapsed from Copyright at the time of writing
**Public Domain in those countries where the Copyright term of the life of the author plus the additional country specific term has lapsed from Copyright at the time of writing
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