SFN08 Abstract – Poster 459.21

Invariance of spike timing precision within neural populations in the early visual system

Gaëlle Desbordes, Jianzhong Jin, Chong Weng, Nicholas A. Lesica, Daniel A. Butts, Garrett B. Stanley, Jose-Manuel Alonso

The timing of spiking activity across neurons is a fundamental aspect of the neural population code. Individual neurons in the retina, thalamus, and cortex have very precise and repeatable responses to the visual stimuli that strongly drive them (down to 1-ms variability), but exhibit degraded temporal precision of firing activity in response to sub-optimal stimuli. In the presence of natural scenes, the activity of individual neurons is sparse and precisely timed across repeated presentations of the visual stimulus, and our group recently showed that this precision of individual neurons is crucial for encoding the visual scene (Butts et al., Nature, 2007). However, in most natural circumstances, the brain does not have access to multiple repetitions of the same identical stimulus, and, therefore, it is the relative precision of spiking across neuronal sub-populations on single trials that is ethologically relevant. While synchrony across neurons in the retina and visual cortex has been reported at various time scales, which can depend on the visual stimulus, the temporal precision of the neural code entering primary visual cortex, and its dependence on the stimulus, are still unknown.

We investigated the spike timing precision across neural populations by recording simultaneously from multiple thalamic neurons likely converging to a common neuronal target in primary visual cortex. A short movie of a natural scene was presented repeatedly to anesthetized cats while recording extracellular activity of multiple single units in the lateral geniculate nucleus (LGN) in vivo. In order to test whether spike timing precision across cells was degraded for suboptimal stimuli, as is the case for individual cells across repeats, each population of cells was stimulated with both a high-contrast version and a low-contrast version of the movie.

We found that spike timing precision across thalamic neurons is not reduced with suboptimal stimuli and remains invariant on the order of 10 ms, even when the response of each cell shows a finer precision which can vary with contrast. Since closely-timed spikes from either a single neuron (Kara & Reid, J. Neurosci., 2003) or several neurons (Alonso et al., Nature, 1996) are more likely to induce a spike in the downstream cortical neuron to which they are projecting, and since recent studies have suggested that synchronous spikes from several thalamic neurons are needed to drive cortical cells to threshold (Bruno & Sakmann, Science, 2006), preserving the relative timing of spikes at a resolution of ~10 ms may be a crucial aspect of the neural code entering primary visual cortex.

Support: This work was supported by a Charles King Trust Postdoctoral Fellowship (D. A. B.), the National Geospatial-Intelligence Agency (G. B. S.), the National Eye Institute (J. M. A.), and the Research Foundation of the State University of New York (J. M. A.).