Originally defined and numbered into 52 regions by the German anatomist Korbinian Brodmann in the early 1900’s, the Brodmann areas of the cerebral cortex are defined by its cytoarchitecture (histological structure and cellular organization).
Before we proceed, it is important to remember that the same Brodmann area numbers in humans and primates often do not translate to other species. In addition, these Brodmann areas have been widely redefined, discussed, debated, and refined exhaustively based on cytoarchitecture, cortical functions, and brain plasticity.
The Brodmann areas were initially based on the cytoarchitectural organization of neurons in the cerebral cortex. Specifically, it was observed that they were organized in distinct groups once the cells were stained using the Nissl method (which consists of basic dyes, notably staining the rough endoplasmic reticulum—also known as Nissl substance—dark blue). Many of these areas of distinct neuronal organization have since been correlated to various cortical functions.
Since there are 52 distinct Brodmann regions, only a few of the major regions will be further elaborated in this article. However, a list of all areas defined can be found below for reference.
Important Brodmann Areas
Primary somatosensory cortex (or Postcentral gyrus) – this is numbered rostral to caudal as 3,1,2. This region is associated with several senses, such as the ones for:
- localization of touch, temperature, vibration, pain
- sensory perception (two-point discrimination, proprioception, etc.) especially the legs, trunk, arms, hands, face and lips
- skilled and coordinated orofacial movement (i.e. whistling)
- motor learning
This are is also known as the primary motor cortex (or Precentral gyrus) (may possibly include part of Area 6). It is responsible for executing motor movements, which includes contralateral finger/hand/wrist or orofacial movements, learned motor sequences, breathing control, and voluntary blinking.
Somatosensory association cortex – Brodmann area 5 is part of the parietal cortex. Associated functions include:
- line bisection judgments
- processing chaotic patterns
- using spatial imagery in deductive reasoning
- motor execution
- bimanual manipulation
- working memory
- language processing
- visuomotor attention
- pain perception
- tactile localization
- saccadic eye movement
Premotor and Supplementary Motor Cortex – this region is critical for the sensory guidance of movement and control of proximal and trunk muscles, and contributes to the planning of complex and coordinated motor movements. This area plays a large role in motor, language, and memory functions, including:
- motor sequencing/planning
- interlimb coordination
- movement learning and initiation
- motor imagery
- speech motor programming
- language processing and switching
- speech perception
- object naming
- word retrieval
- lexical decision on words and pseudowords
- syntactical processing
- working memory
- mnemonic rehearsal
- episodic long-term memory
- topographic memory
- visuospatial and visuomotor attention
- attention to human voices
Note: The “Motor Association Cortex” includes areas 6, 8, 44, and 45. This association cortex is involved in movement throughout the body, including motor speech movements.
Dorsolateral/anterior prefrontal cortex (DLPFC) – This region is the highest cortical area responsible for motor planning, organization, and regulation, and sustaining attention and working memory. The DLPFC plays an important role in:
- integrating sensory and mnemonic information
- regulation of intellectual function and action
- the act of deception and lying
In sum, all complex mental activities require crosstalk between cortical and subcortical circuits that are connected to the DLPFC.
Anterior prefrontal cortex – involved in strategic processes of memory retrieval and executive functions, such as
- task flexibility
- problem solving
- working memory
- processing emotional stimuli
- inferential reasoning
- decision making
- calculation of numerical processes
There is a significant role of Areas 9 and 10 in memory encoding and retrieval, and area 10 is thought to control and manipulate event and time-based prospective memory (metamemory), and allow “intentional forgetting.”
Area 10 is also involved in attending to sensory stimulation and use of language (generating sentences, word-stem completion, verbal fluency, syntactic processing, and metaphor comprehension).
Primary visual cortex (V1) – the visual cortex is located in the occipital lobe in the back of the brain, and contains a well-defined map of the spatial information required for vision.
Primary auditory cortex / Superior Temporal Gyrus (part of Wernicke’s area) – this region is situated close to the external ear and involves complex language and auditory processing.
Fusiform Gyrus / Occipitotemporal Gyrus – this region is largely involved in:
- processing of color information
- face and body recognition
- word and number recognition
Areas 22, 39, 40
Wernicke’s area – the gyri that comprise this area may be larger or smaller in different people and itis responsible for speech fluency. More precisely, this area allows you to string words together in complete and sensical sentences. An easy way to temember is to think of “Wordy Wernicke”.
Broca’s area – this region is associated with the praxis of speech (motor speech programming). This includes:
- being able to put together the binding elements of language
- selecting information among competing sources
- sequencing motor/expressive elements
- cognitive control mechanisms for syntactic processing of sentences
- construction of complex sentences and speech patterns
You can remember it by thinking of “Broken boca” where boca means ‘mouth’ in Spanish.
All Brodmann areas
- Areas 3, 1 & 2 – Primary Somatosensory Cortex (frequently referred to as Areas 3, 1, 2 by convention)
- Area 4 – Primary Motor Cortex
- Area 5 – Somatosensory Association Cortex
- Area 6 – Premotor cortex and Supplementary Motor Cortex (Secondary Motor Cortex) (Supplementary motor area)
- Area 7 – Somatosensory Association Cortex
- Area 8 – Includes Frontal eye fields
- Area 9 – Dorsolateral prefrontal cortex
- Area 10 – Anterior prefrontal cortex (most rostral part of superior and middle frontal gyri)
- Area 11 – Orbitofrontal area (orbital and rectus gyri, plus part of the rostral part of the superior frontal gyrus)
- Area 12 – Orbitofrontal area (used to be part of BA11, refers to the area between the superior frontal gyrus and the inferior rostral sulcus)
- Area 13 and Area 14* – Insular cortex
- Area 15* – Anterior Temporal Lobe
- Area 16 – Insular cortex
- Area 17 – Primary visual cortex (V1)
- Area 18 – Secondary visual cortex (V2)
- Area 19 – Associative visual cortex (V3,V4,V5)
- Area 20 – Inferior temporal gyrus
- Area 21 – Middle temporal gyrus
- Area 22 – Superior temporal gyrus, of which the caudal part is usually considered to contain the Wernicke's area
- Area 23 – Ventral posterior cingulate cortex
- Area 24 – Ventral anterior cingulate cortex.
- Area 25 – Subgenual area (part of the Ventromedial prefrontal cortex)
- Area 26 – Ectosplenial portion of the retrosplenial region of the cerebral cortex
- Area 27 – Piriform cortex
- Area 28 – Ventral entorhinal cortex
- Area 29 – Retrosplenial cingulate cortex
- Area 30 – Part of cingulate cortex
- Area 31 – Dorsal Posterior cingulate cortex
- Area 32 – Dorsal anterior cingulate cortex
- Area 33 – Part of anterior cingulate cortex
- Area 34 – Dorsal entorhinal cortex (on the Parahippocampal gyrus)
- Area 35 – Perirhinal cortex (in the rhinal sulcus)
- Area 36 – Ectorhinal area, now part of the perirhinal cortex (in the rhinal sulcus)
- Area 37 – Fusiform gyrus
- Area 38 – Temporopolar area (most rostral part of the superior and middle temporal gyri)
- Area 39 – Angular gyrus, considered by some to be part of Wernicke's area
- Area 40 – Supramarginal gyrus considered by some to be part of Wernicke's area
- Areas 41 and 42 – Auditory cortex
- Area 43 – Primary gustatory cortex
- Area 44 – Pars opercularis, part of the inferior frontal gyrus and part of Broca's area
- Area 45 – Pars triangularis, part of the inferior frontal gyrus and part of Broca's area
- Area 46 – Dorsolateral prefrontal cortex
- Area 47 – Pars orbitalis, part of the inferior frontal gyrus
- Area 48 – Retrosubicular area (a small part of the medial surface of the temporal lobe)
- Area 49 – Parasubicular area in a rodent
- Area 52 – Parainsular area (at the junction of the temporal lobe and the insula)
(*) Area only found in non-human primates.
Lesions of Brodmann Areas
A lesion in this area would cause:
- loss of vibration, proprioception and fine touch (since 3rd order neurons of the medial-lemniscal pathway cannot synapse in the cerebral cortex)
- potentially hemineglect if the non-dominant hemisphere is affected.
A lesion in this area would cause paralysis of the contralateral side of the body, including facial palsy, arm or leg monoparesis, and hemiparesis.
A lesion in the left superior parietal lobe would cause ideomotor apraxia, which is the loss of ability to produce purposeful, skilled movements as a result of brain pathology not due to physical weakness, paralysis, lack of coordination or sensory loss. Astereognosis (also known as tactile agnosia) is also possible, which would lead to loss of ability to recognize objects by feeling or handling them.
A lesion here would affect sensory guidance of movement and control of proximal and trunk muscles. Damage of the lateral premotor area would result in kinetic apraxia (which would appear as coarse or unrefined movements that no longer have the appearance of being practiced over time). Other lesions would cause loss of other functional processes described.
A lesion in the DLPFC will create difficulties in inhibiting responses and result in dysexecution syndrome, which leads to problems with affect, social judgement, executive memory, abstract thinking, and intentionality.
A lesion here is similar to what would be seen in Area 9, since the two areas are associated.
Depending on where and how damage and lesions occur to this region, partial or complete cortical blindness can result; for example, if the upper bank of the calcarine sulcus is damaged, then the lower bank of the visual field is affected.
Lesions in this area results in:
- difficulty finding words
- semantic paraphasias
- prosopagnosia (the acquired inability to recognize faces)
- disturbances in drawing
Areas 22, 39, 40
A lesion here causes language disorders characterized by fluent speech paraphasias where a lot of words are jumbled and nonsensical sentences are spoken. There may also be language comprehension deficits.
Areas 44, 45
Lesions in this area cause Broca’s aphasia: a deficit in the ability to speak and produce the proper words/sounds, even though the afflicted person maintains the ability to comprehend language and to mentally formulate proper sentences.