Functional Neuroanatomy Pt 1

Functional divisions of the brain

• parts of brain dedicated to specific fxns

• not organised as individual centres but as parts of interacting networks

Ways to divide Cerebral cortex

• phrenology

• Broadmann areas

• gyri and sulci

Broadmann Areas

• brain divided into 52 areas

• based on size, shape and type of neurons in cortex

Functional divisions of cerebral cortex

• Primary areas

• Association areas = secondary areas

Primary areas

• ± 10% of cortex

• Primary motor area

• Primary sensory areas

Primary motor area (M1)

• responsible for execution of motor tasks

• located in precentral gyri in frontal lobes (BA4)

• control of the skeletal muscles on the contralateral side of the body

• source of descending motor pathways projecting to lower levels of nervous system

• contains motor homonculus

Primary sensory areas

• precise relationship with specific body areas

• receive sensory info from receptors in periphery

• little interpretation of meaning

Primary somatosensory area (S1)

• located in postcentral gyri in parietal lobes (BA 1,2,3)

• contralateral representation

• contains sensory homunculus

Primary auditory area (A1)

Heschl’s gyrus in temporal lobe (BA 41, 42)

Primary visual area (V1)

In occipital lobes (BA 17)

Olfactory area

involved in smell sensation

Gustatory area

• involved in taste sensation

Lesion in primary areas

• complete or partial deficit in corresponding motor or sensory modality

• clearly defined deficits

• e.g. reduced perception of stimuli, weakness

Association areas

• specific areas adjacent to primary motor and sensory area

  • receive input from primary areas

  • higher order processing

• larger association areas = broader fxn

Unimodal

primarily receives input from a single sensory area

Heteromodal

receives input from multiple sensory or multimodal areas

Association areas in frontal lobe

• Premotor area

• Supplementary motor area

• Broca’s area

• Prefrontal area

Premotor cortex

= motor association area

• anterior to primary motor area

• planning of voluntary movement

• integration and interpretation of motor info

• contains motor maps for movement of larger muscle groups

Supplementary motor area (SMA)

• anterior to M1 & superior to premotor area (medial surface)

• maps for postural stabilization

• initiation of speech

Broca’s Area

(BA 44 & 45)

• in dominant hemisphere (usually left)

• pars triangularis & opercularis of IFG

• programs speech movements and phoneme sequencing

Prefrontal area

• anterior to premotor area

• role in executive functions, working memory and personality

Association areas in the parietal lobe

• somatosensory association cortex

• posterior parietal cortex

• multimodal association area

Somatosensory association cortex

• BA 5

• adjacent to primary somatosensory area

• interpretation of sensory info

• lesion can result in astereognosia (inability to recognize objects by touch)

Posterior parietal cortex

• BA 7

• Somatosensory & visual integration

• Visuospatial perception & attention

  • Representation & manipulation of objects

  • Perception of movement

• Lesions may result in:

  • Neglect syndrome

  • Apraxia

Inferior parietal cortex

• BA 39, 40

• Multimodal association cortex

  • visual, auditory & somatosensory info

• Role in receptive language in dominant hemisphere

  • phonology, reading, spelling

• Role in spatial & symbolic representation of abstract concepts

Superior Longitudinal Fasciculus/Arcuate fasciculus

• Important tracts connecting inferior parietal cortex (IPC) to inferior frontal gyrus (IFG) and superior temporal gyrus (STG)

• connects frontal, parietal and temporal lobes

• how Wernicke’s and Broca’s area are interconnected

Visual association cortex

• in occipital lobe

• surrounding primary visual cortex on medial surface and extending onto lateral surface

• interpretation of what we see

  • dorsal stream - where? location & movement of objects

  • ventral stream - what? form and colour of objects

Association areas in temporal lobe

• auditory association cortex

• fusiform gyrus

Auditory association cortex

• Distinguish sounds as speech, music or noise

• Wernicke’s area

  • superior temporal gyrus

  • assigning meaning to symbols

  • comprehension of language: spoken, written & gestures

Fusiform gyrus/occipitotemporal gyrus

• Inferior surface of temporal lobe

• Synthesizes & elaborates complex aspects of info

• e.g., link visual object/word/face to meaning

Lesions in association areas

• more complex result

• e.g., higher cognitive ability, personality

  Example

• visual agnosia following lesion in fusiform gyrus

  • can see object & can describe it but don’t know what it is

  • may be able to recognise it using touch, smell, …

  • prosopagnosia: visual agnosia for faces