for different categories of objects (people,animals,tools) depends partly
on different regions of the left temporal lobe that are below the classic
language centers (Damasio et al.1996),and a discrete region of the left
precentral gyrus of the insula (buried within the Sylvian fissure and not
visible in figure 13.1) is known to be specialized for motor planning of
speech (Dronkers 1996).Thus,one can no longer speak of Broca’s area
(44 and 45 in figure 13.1) as the only,or even the primary,motor lan-
guage (i.e.,speech) association area,or of the cerebellum as involved
purely in motor coordination.It is important to note,however,that figure
13.1 is simplified,and that various aspects of language are multifaceted,
extremely complex,and distributed across all lobes of the brain,as well
as both hemispheres (but mainly the left).Nevertheless,this illustration
accurately identifies nodal areas that contribute to specific aspects of
language in most people.
The map of the human figure (or homunculus) reflects the basic orga-
nization of the primary somatosensory cortex (S) in the parietal lobe,
which is a mirror image of the primary motor cortex (M) of the frontal
lobe.These two lobes-cortices are separated by the central sulcus that
courses down the midline of the homunculus.Sensory components of
language include hearing,reading,and comprehending words.Areas 41
and 42 (Heschl’s convolutions),which are buried within the Sylvian
fissure,are auditory cortices of the temporal lobe that receive initial
inputs from all types of sounds in both hemispheres.Subsequently,the
auditory association cortex that can be seen on the outside surface of the
temporal lobes (area 22) further interprets these acoustic stimuli,with
analysis of spoken words being undertaken largely by the left hemi-
sphere.Damage to area 22 on the left side therefore results in word deaf-
ness,in which the individual’s hearing is fine,but words are perceived as
mere noises that have no meaning.These effects are severest if area 22
in both hemispheres is damaged.Another auditory association area long
thought to be important for interpreting language sounds,the planum
temporale,is directly behind areas 41 and 42 within the Sylvian fissure
(again,not visible on the lateral surface of the temporal lobe).Area 39
(angular gyrus) in the left hemisphere is important in reading words,
similar to area 22’s role in hearing them.Thus a lesion in this area results
in word blindness (alexia),in which a person can see well but cannot
read (and therefore cannot write).
Together,areas 22 and 39 of the left hemisphere constitute Wernicke’s
area,damage to which results in classic receptive aphasia,or loss of audi-
tory and visual comprehension of language.Area 39 is located in the pari-
etal lobe,as is area 40 (supramarginal gyrus) directly in front of it.Both
areas send and receive information from many other cortical regions;
that is,they are association cortex.Area 40 is crucial for understanding199 Hominid Brain Evolution and the Origins of Music