Cells in the LGN exhibit two modes of firing, burst and tonic. In the LGN, Sherman (2001) has suggested that burst mode may be used as a "wake up call" alerting an animal to relevant stimuli that are then analyzed further when LGN cells are in tonic mode. In this study we examined the presence of bursts under different behavioral conditions. Single LGN cells were recorded while monkeys made saccades freely in complete darkness (FREE) or to a target located in the LGN cell's receptive field (GO). A change in fixation spot color signaled the monkeys to either remain fixated (red) or to shift gaze to the target (green). Bursts, defined as a series of spikes having interspike intervals of 4ms or less preceded by a period of silence lasting at least 100ms, were recorded during both the fixation period and saccade period for both the GO and FREE tasks and also following the cue in the GO task. Bursts were seen in 94% of cells (59/63) recorded in the FREE task and 28% of cells (26/90) in the GO task. Bursts were seen in M, P and K (blue-ON) cells. The average number of bursts per second was 0.36 for cells recorded in the FREE task and 0.08 recorded in the GO task. Bursts were seen in all behavioral epochs in both tasks and burst number did not differ significantly between epochs. Our results demonstrate that although a significant fraction of LGN cells burst in the awake state, bursting appears more linked to behavioral state than to task demands, at least under conditions where monkeys are familiar with the task.
ASJC Scopus subject areas
- Sensory Systems