Sensory information processing in neocortex is associated with
synchronized gamma frequency firing of sensory cortical units
frequency oscillations of the field potentials. Different
aspects of the gamma
activity (20-80 Hz) have been suggested as correlates of
attention, arousal and
sensory binding. It is clear that attention has a modality
while arousal has a more general effect on the sensory systems.
We used an
experimental conditioning paradigm to separate these
differential effects of
attention and arousal on spontaneous neocortical gamma activity.
field potentials with epidural electrodes placed above the
areas of cats. The animals performed a simple instrumental
conditioning task with different modality (visual and auditory)
stimuli. When they attended to the auditory conditioned
stimulus, both frequency
and power increase of spontaneous gamma activity were detected.
However when they
attended visual, we found no power increase of gamma activity
auditory areas, while the frequency increase was the same as in
auditory" condition. We conclude that the power modulation of
gamma activity is
modality specific and thus can be attributed to selective
attention, whereas the
frequency modulation of gamma activity shows no modality
specificity, it is
influenced by the arousal level.