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S. Martinez-Conde, S.L. Macknik and D.H. Hubel

Department of Neurobiology, Harvard Medical School

Bursts of spikes in the LGN and area V-1 are correlated with microsaccades during visual fixation in the awake monkey

When images are stabilized on the retina, visual perception fades. During voluntary visual fixation, however, constantly occurring small eye movements, or microsaccades, somehow prevent this fading.

We have investigated the relationship between microsaccades during visual fixation and the responses of neurons in visual area V-1 and the lateral geniculate nucleus (LGN) in the awake behaving macaque monkey.

Experiments were carried out in two alert rhesus monkeys trained to fixate their gaze on a small spot. Visual stimuli consisted of stationary bars centered over the receptive fields of cells in area V-1 and the LGN. We monitored eye movements during visual fixation with a monocular eye coil while recording extracellularly from single neurons.

Our results suggest that during visual fixation microsaccades can visually drive neurons by moving their receptive fields across stationary stimuli. Microsaccades produced maximal responses in V-1 neurons when the bar centered over their receptive fields was oriented to match the cell's optimal orientation. In the LGN, however, microsaccades induced visual responses for stationary bars of any orientation. Bursts of spikes, moreover, were more closely associated with preceding microsaccades than were lone spikes, suggesting that bursts of spikes are more reliable as neural signals than are lone spikes, both in the LGN as well as in area V-1.

Supported by grant EY00605 from NIH to DHH and training grants from NIH and MEC-FPI to SLM and SM-C.

Tony Zador
Sat Mar 27 10:58:21 PST 1999