Neurological Examination, clinical cases and neuropsychological ...

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Function of Primary auditory cortex
As with other primary sensory cortical areas, auditory sensations reach perception only if
received and processed by a cortical area. Evidence for this comes from lesion studies in
human patients who have sustained damage to cortical areas through tumors or strokes, or
from animal experiments in which cortical areas were deactivated by cooling or locally
applied drug treatment. Damage to the Primary Auditory Cortex in humans leads to a loss of
any awareness of sound, but an ability to react reflexively to sounds remains as there is a
great deal of subcortical processing in the auditory brainstem and midbrain.
Neurons in the auditory cortex are organized according to the frequency of sound to which
they respond best. Neurons at one end of the auditory cortex respond best to low
frequencies; neurons at the other respond best to high frequencies.
There are multiple auditory areas (much like the multiple areas in the visual cortex), which
can be distinguished anatomically and on the basis that they contain a complete "frequency
map." The purpose of this frequency map (known as a tonotopic map) is unknown, and
is likely to reflect the fact that the cochlea is arranged according to sound frequency. The
auditory cortex is involved in tasks such as identifying and segregating auditory "objects" and
identifying the location of a sound in space.
Human brain scans have indicated that a peripheral bit of this brain region is active when
trying to identify musical pitch. Individual cells consistently get excited by sounds at
specific frequencies, or multiples of that frequency.
The auditory cortex is an important yet ambiguous part of the hearing process. When the
sound pulses pass into the cortex the specifics of what exactly takes place are unclear.
Distinguished scientist and musician James Beament puts it into perspective when he
writes, “The cortex is so complex that the most we may ever hope for is to understand it
in principle, since the evidence we already have suggests that no two cortices work in
precisely the same way."
In hearing process, multiple sounds are being absorbed simultaneously. The role of the
auditory system is to decide which components form the sound link. Many have surmised
that this linking is based on location of sounds; however, there are numerous distortions
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of sound when reflected off different mediums, which makes this thinking unlikely.
Instead, the auditory cortex forms groupings based on other more of the reliable,
fundamentals. In music for example, this would include harmony, timing, and pitch.
The primary auditory cortex lies in the posterior half of the superior temporal gyrus and
also dives into the lateral sulcus as the transverse temporal gyri (also called
Heschl's gyri).
The primary auditory cortex is located in the temporal lobe. There are additional areas of
the human cerebral cortex that are involved in processing sound, in the frontal and
parietal lobes.
Brodmann area 41 is also known as the anterior transverse temporal area 41 (H).
It is a subdivision of the cytoarchitecturally‐defined temporal region of cerebral cortex,
occupying the anterior transverse temporal gyrus (H) in the bank of the lateral sulcus on
the dorsal surface of the temporal lobe. Brodmann area 41 is bounded medially by the
parainsular area 52 (H) and laterally by the posterior transverse temporal area 42 (H).
Brodmann area 42 is also known as the posterior transverse temporal area 42 (H). It is a
subdivision of the cytoarchitecturally‐defined temporal region of cerebral cortex, located in
the bank of the lateral sulcus on the dorsal surface of the temporal lobe. Brodmann area
42 is bounded medially by the anterior transverse temporal area 41 (H) and laterally by the
superior temporal area 22.
The primary auditory cortex is tonotopically organized, which means that
neighboring cells in the cortex respond to neighboring frequencies. This is a
fascinating function which has been preserved throughout most of the audition
circuit. This area of the brain is thought to identify the fundamental elements of
music, such as pitch and loudness. This makes sense, as this is the area which
receives direct input from the medial geniculate nucleus of the thalamus. The
secondary auditory cortex has been indicated in the processing of
“harmonic, melodic and rhythmic patterns.” The tertiary auditory cortex
supposedly integrates everything into the overall experience of music
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Broca's area is a region of the hominid brain
with functions linked to speech production.
The production of language has been linked to the
Broca’s area since Pierre Paul Broca reported
impairments in two patients. They had lost the
ability to speak after injury to the posterior inferior
frontal gyrus of the brain. Since then, the
approximate region he identified has become
known as Broca’s area, and the deficit in language
production as Broca’s aphasia. Broca’s area is now
typically defined in terms of the pars opercularis
and pars triangularis of the inferior frontal gyrus,
represented in Brodmann’s
cytoarchitectonic map
as areas 44 and 45. Studies of chronic aphasia have
implicated an essential role of Broca’s area in
various speech and language functions. Further,
functional MRI studies have also identified
activation patterns in Broca’s area associated with
various language tasks. However, slow destruction
of the Broca's area by brain tumors can leave
speech relatively intact suggesting its functions can
shift to nearby areas in the brain.
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