hyperacusistxt

1 - Inhibitory neurotransmitters
High aerobic metabolism in the inferior colliculus must
support some essential function such as that
suggested by Fisch (1970) to continually monitor
acoustic changes in the environment, even during
sleep [1]. Feng (1992) proposed that signal
processing in the inferior colliculus plays a key role in
representation of space, and that this involves
moment to moment damping of some signals to
enhance focus on sounds of greater importance [2].

Researchers at the molecular level (for example
Faingold et al. 1991 and Zhang & Feng 1998) have
found that inhibitory as well as excitatory
neurotransmitters work together in the inferior colliculi
to modulate responses of neurons that detect sound
onset; ongoing signals of the same frequency and
intensity are detected but not transmitted further [3, 4].

The hypersensitivity to sounds displayed by some
autistic children may represent loss of inhibitory
function. Inability to distinguish sound onset then
relegate it to background awareness could also be
part of the difficulty in recognizing boundaries
between words and syllables in spoken language.

Caspary et al. (1995) provided data showing decline
with advancing age of neurotransmitter function in the
inferior colliculus that may lead to loss of the capacity
to detect and extract meaningful signals from
background noise [5]. They pointed out that this
leads to difficulty following a conversation in a noisy
environment and may be the reason some elderly
people withdraw from participation in society. The
same or similar disability may lead children with autism
to avoid social contact.

Fisch L (1970) The selective
and differential vulnerability of
the auditory system.
Feng AS (1992) Information
processing in the auditory
brainstem.
Faingold CL et al. (1991)
Functional pharmacology of
inferior colliculus neurons.
Zhang H, Feng AS (1998)
Sound direction modifies the
inhibitory as well as the
excitatory frequency tuning
characteristics of single
neurons in the frog torus
semicircularis (inferior
colliculus).
Caspary DM, Milbrandt JC,
Helfert RH (1995) Central
auditory aging: GABA changes
in the inferior colliculus.

Fisch L (1970) The selective and differential vulnerability of the auditory system. In GEW
Wolstenholm and J Knight, (Eds), Sensorineural Hearing Loss: A Ciba Foundation
Symposium (pp 101-116). London: Churchill.
Feng AS (1992) Information processing in the auditory brainstem. Current Opinion In
Neurobiology 2:511-515.
Faingold CL, Gehlbach G, Caspary DM (1991) Functional pharmacology of
inferior colliculus neurons. In R.A. Altschuler et al. Neurobiology of Hearing:
The Central Auditory System. New York: Raven Press, pp 223-252 (chapter
10).
Zhang H, Feng AS (1998) Sound direction modifies the inhibitory as well as
the excitatory frequency tuning characteristics of single neurons in the frog
torus semicircularis (inferior colliculus). Journal of Comparative Physiology.
A, Sensory, Neural, and Behavioral Physiology 182:725-735.
Caspary DM, Milbrandt JC, Helfert RH (1995) Central auditory aging: GABA
changes in the inferior colliculus. Experimental Gerontology 30:349-360.