az akusztikus ingerek hatása a lassú alvási oszcillációra - Kutatás

SUMMARY
During sleep – according to classical hypotheses – our inside world is largely
dissociated from the outside environment. In slow wave sleep, acoustical signals are gated at
thalamic level and do not reach the neocortex. During deep sleep neocortex expresses a
characteristic slow oscillation built up of cyclic periods of active and inactive states playing
an important role in brain homeostasis, memory consolidation and may be in relation with the
generation of epileptic seizures.
If auditory cortex would not process acoustical stimuli, emergency signals could not
waken the sleeping subject, and thus, chances for staying alive would be considerably
decreased. At the same time, if every noise could waken the subject, he would suffer from
serious sleep deprivation, also producing severe physiological problems. Based on our
hypothesis, a more sophisticated strategy should exist in the mammalian brain, allowing
acoustical information to reach neocortical levels and to ensure information processing crucial
for the survival of the subject.
In the present study we investigated the impact of acoustical stimuli on cortical slow
oscillation of cats and monkeys in ketamine-xylazine anesthesia. We studied auditory and
secondary somatosensory cortices in monkeys, auditory cortex and suprasylvian association
area (area 7) in cats. Changes in oscillatory patterns of the different neocortical areas have
been explored by the analysis of cortical field potentials obtained with multiple channel
microelectrodes.
We found evoked potentials to acoustical stimuli in the primary auditory cortex, and
observed that these inputs induced active states of slow oscillation, i.e. synchronized the
activity of large amount of cortical neurons. Furthermore, analysis of slow oscillation in
somatosensory cortex and association area showed that the modulated activity of primary
auditory cortex is able to synchronize oscillation of certain surrounding cortical areas.
Our results suggest that acoustic evoked states in sleep might play an important role in
wakening as well as in sleep protecting mechanisms. The influence of the auditory cortex on
the oscillation synchrony in the surrounding association and somatosensory areas might
prepare these latter cortices to a more efficient processing of the further arriving information.
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