Visual cortical hypersynchronous bursting as an index of shifts in behavioral state.

Photically evoked after-discharge (PhAD) bursting was examined in lightly restrained albino rats during habituation of a leg flexion response. The initial effect of iterative footshock (200 trials, 0.17 mA, 2.5 msec duration, separated by 1.0 sec) was to block PhAD bursting. As response habituation developed PhAD reappeared at reduced levels, subsequently returning to control levels as habituation progressed and became complete. The number of spindles per PhAD burst was suppressed for a brief period which coincided with response sensitization. These results are interpreted as demonstrating that phasic shifts in behavioral state are reflected by PhAD parameters. In addition, the possible relationship between cortical information processing and PhAD bursting is discussed with reference to putative neural mechanisms involved.