High-resolution two-dimensional spatial mapping of cat striate cortex using a 100-microelectrode array

Much of our understanding of the visuotopic organization of striate cortex results from single-electrode penetrations and serial recording of receptiv e field properties. However, the quality of these maps is limited by imprec ision in quantifying electrode position, combining data from multiple lamin ae, and eye drift during the measurement of the receptive field properties. We have addressed these concerns by using an array of 100 closely spaced m icroelectrodes to investigate the two-dimensional visuotopic organization o f layer IV in cat striate cortex. This array allowed simultaneous measureme nt of the receptive field properties of multiple single units on a regularl y spaced grid. We found the relationship between cortical and visual space to be locally non-conformal: the receptive field locations associated with a closely spaced line of electrodes appeared randomly scattered in visual s pace. To quantify the scatter, we fitted a linear transformation of electro de sites onto the associated receptive field locations. We found that the d istribution of the difference between the predicted receptive field locatio n and the measured location had standard deviations of 0.59 degrees and 0.4 5 degrees in the horizontal and the vertical axes, respectively. Although i ndividual receptive field positions differed from the predicted locations i n a non-conformal sense, the trend across multiple receptive fields followe d the maps described elsewhere. We found, on average, that the 13 mm(2) of cortex sampled by the array mapped onto a 5.8-degrees(2) region of visual s pace. From the scaling of this map and a combination of the statistics of t he receptive field size (2.7 +/- 1.5 degrees(2)) and scatter, we have explo red the impact of electrode spacing on the completeness and redundancy in c overage of visual space sampled by an array. The simulation indicated an ar ray with 1.2-mm spacing would completely sample the region of visual space addressed by the array. These results have implications for neuroprosthetic applications. Assuming phosphene organization resembles the visuotopic organization, remapping of visual space may be necessary to accommodate the scatter in phosphene locat ions. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved .