Satellite workshop of the Japan Neuroscience Meeting : Okazaki 2006
第35回生理研コンファレンス / 統合脳 国際シンポジウム/日本神経科学会大会サテライトワークショップ(岡崎)
2006.7.24-26

Clustering of color-selective cells in macaque area V4: analysis with multiple single-unit recordings

Yasuyo Kotake, Hiroshi Morimoto, Hiroshi Tamura, Ichiro Fujita

Grad. Sch. Frontier Biosciences
Grad. Sch. Engineering Science, Osaka Univ.; CREST, JST, Japan

It is unclear how color selective cells are spatially arranged in area V4. The initial studies reported that V4 cells are clustered into columns and arranged orderly across the cortex according to their preferred color. A later study, however, found no evidence for this type of organization. To reexamine this issue, we quantitatively assessed the degree of clustering of color selective cells in V4 with multiple single-unit recording techniques in anesthetized monkeys (Macaca fuscata). The majority (91/127, 72%) of the recorded cells exhibited color selectivity (p<0.05). We employed the color discrimination index (CDI), which characterizes a cell’s stimulus discrimination ability against the trial- to-trial response variability. The CDIs were positively correlated between nearby cells (n=404, r=0.38, p<0.001), indicating that nearby cells showed a similar degree of color tuning. We then analyzed similarity of color preferences for nearby color-selective cell pairs (n=202) by calculating the correlation coefficient of their responses to 27 colors. The correlation coefficients of nearby pairs (median, 0.32) were greater than those of distant pairs (median, 0.11; p<0.001). Nearby cells as a whole weakly shared color preferences. To examine further the congruency of color preference among cells in a local region, we measured the Euclidean distance on a MacLeod-Boynton chromaticity diagram between the optimal colors for nearby cells, and calculated the standard deviation (SD) of the distances among cells at each recording site. The distribution of the SDs was bimodal. The results suggest that V4 contains two types of local regions of color-selective cells: one where nearby cells share color preferences and one where color preferences are diverse. Alternatively, clusters of V4 cells with different color preferences may occasionally abut at singularity points, similar to orientation columns with different preferences that meet at a pinwheel centers in V1.

This work was supported by CREST, JST and MEXT