23
FUNCTIONAL
ORGANIZATION AND
PLASTICITY OF
AUDITORY CORTEX
.
Remarkable as our cerebral cortex is in many respects, its ability to self-organize in
response to extrinsic stimuli is perhaps the most astonishing property of all. The three
chapters in this section are all impressive testimony to this ability. The effects of musical
experience can be found on various levels: in the gross-anatomical differences between
professional musicians with absolute pitch^1 (Chapter 24, this volume) to the subtle func-
tional differences after musical training found with magnetoencephalography^2 (Chapter
25, this volume) or transcranial magnetic stimulation^3 (Chapter 26, this volume). Of
course, even the ability to learn and memorize a simple tune is an expression of the brain’s
ability to change with musical experience. In this case, the changes would have to be sought
in even finer modifications of synaptic strength in distributed cortical networks.
Basic principles of cortical plasticity
The tenet that learning and memory is based on changes of synaptic efficacy was prop-
agated, among others, by Hebb.^4 More specifically, he postulated that the conjunction of
pre- and postsynaptic activity contributes to a strengthening of synaptic connections.
Hebb’s ideas were applied to many different areas of neuroplasticity, but perhaps most
prominently so in the field of visual cortical plasticity. Developing visual cortex became a
model system for the study of neural plasticity when Wiesel and Hubel had established
many of the fundamental facts, such as ocular dominance plasticity after monocular lid
closure.^5 The development of orientation selectivity was also proposed early on as an
example of experience-dependent plasticity at the single-neuron level^6 and was later shown
to follow Hebbian rules.7,8
Improved auditory abilities in the blind
Deprivation in one sensory modality, such as vision, can also lead to dramatic reorganization
in other modalities, such as hearing or touch.^9 The mechanisms of cross-modal plasticity of