Precision , Reliability and Information Theoretic Analysis of Visual Thalamic and Cortical Neurons

High-order statistics of neural responses allow one to gain insight into neural function that may not be evident from firing rate alone. In this study, we compare the precision, reliability, and information content of spike trains from Xand Y-cells in the lateral geniculate nucleus (LGN) and layer IV simple cells of area 17 in the cat. Using a stochastic, contrast-modulated Gabor patch, we found that layer IV simple cells respond as precisely as their primary inputs, LGN X-cells, but less reliably. LGN Y-cells were more precise and reliable than LGN X-cells. Also, we found that within each LGN cell type, (1) responses to the same stimulus were nearly identical if they shared the same center sign; (2) responses of neurons with the same center sign were nearly identical to the responses of neurons of opposite center sign if the stimulus’ contrasts were inverted. These results suggest simple cells receive highly precise and synchronous LGN input, resulting in precise responses. Nonetheless, we found that the response precision of simple cells was greater than expected. Finally, we made information theoretic calculations of our cell responses and found that (1) LGN X-cells encoded information at half the rate of LGN Y-cells but 2.5 times the rate of layer IV simple cells; (2) LGN cells encoded information in their responses using temporal patterns while simple cells did not; and (3) simple cells used more of their information capacity than LGN X-cells. We propose mechanisms that simple cells might use to ensure high precision. Page 2 of 67