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Functional specialization is a common characteristic of
the cerebral cortex. Globally, regions are specialized
to perform particular sensory or motor functions.
Within extrastriate visual cortex of humans, monkeys
and cats, areas have been identified that are further
specialized for spatial, motion, and pattern processing.
The behavioural correlate for such functional
specializations, or a “division of labor”, within
auditory cortex is largely unknown. The long-term goal
of this work is to elucidate the behavioural “division
of labor” within auditory cortex and determine the
relative contributions that the different auditory
fields make to acoustic behaviours. These results, when
combined with investigations of underlying cerebral
connections, will provide evidence for, or refute, which
hierarchical or network theories best explain processing
in auditory cortex. We are combining a battery of
psychophysical tests, reversible deactivation, pathway
tracing, and activity-dependent measures to dissect the
functional plan of auditory cortex and the specific
cerebral regions mediating audiomotor responses
controlled by the superior colliculus.
 We are examining the
thirteen commonly recognized regions of
acoustically-responsive cortex: the four tonotopic
fields (AI, AAF, PAF & VPAF) and nine non-tonotopic
areas (AII, AES, DZ, dPE, iPE, vPE, VAF, IN, & T). Two
general classes of tasks are being used to determine if
areas specialized for “spatial and motion” and “pattern
and temporal” processing can be identified.
I)
Spatial & Motion Processing. Reversible cooling
deactivation is being used determine the areas of
auditory cortex responsible for the accurate reorienting
of the head to an acoustic stimulus and the
discrimination of stationary and moving sounds. Tasks
require the subject to: 1) reorient its head to an
acoustic stimulus; 2) accurately localize a stationary
acoustic stimulus without an audiomotor response; and 3)
accurately discriminate the direction of a moving
acoustic stimulus.
II)
Pattern & Temporal Processing. Reversible cooling
deactivation is being used to determine the auditory
cortex areas mediating pattern and temporal processing.
Tasks require the subject to: 1) discriminate temporal
patterns of the same duration; 2) discriminate between
acoustic stimuli that differ only in their temporal
duration; and 3) discriminate between different natural
vocalizations.After behavioural
training, pairs of cooling loops are bilaterally
implanted over discrete areas of auditory cortex. These
loops will both be bilaterally and unilaterally
deactivated, and any resulting impairments identified.
At the conclusion of testing, 2-deoxy-14C-glucose
(2DG) uptake techniques will be used to determine
deactivation extent.
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