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Dynamics of orientation tuning in V2 neurons of macaque monkeys



Conference Title

Society of Neuroscience Annual Meeting


Society of Neuroscience


Washington, D.C. / November 15-19, 2008

Publication Date / Copyright Date



Orientation tuning of V1 neurons in macaque monkeys exhibits complex dynamical changes in the timing of global enhancement, global and tuned suppression, sharpening of tuning, and small shifts in preferred orientation (Ringach et al, 1997; 2003; Shapley et al, 2004). This dynamics of orientation tuning is thought to reflect the timing and strength of multiple inputs arriving via intracortical and/or feedback connections (Ben-Yishai et al, 1995; Somers et al, 1995; Troyer et al, 1998; McLughlin et al, 2000; Ringach et al, 2003; Shapley et al, 2004). We previously found that the orientation tuning of the majority of V2 neurons in macaque monkeys is similar to that of V1 units, but that a substantial proportion of V2 neurons exhibit ‘complex’ orientation tuning properties, e.g., sensitivity to orthogonal orientation. In this study we examined the temporal dynamics of orientation tuning in V2 neurons of mature adult monkeys using the reverse correlation technique in orientation domain similar to that employed by Ringach et al (2003). Thus far we found that orientation tuning emerged after a delay of typically 55 msec (as early as 30 msec and as late as 60 msec), peaked around 80 msec (varied between 50 and 110 msec), and persisted for about 80-90 msec (varied between 50 and over 130 msec). These are in contrast to comparable values in V1, i.e., 30-45 msec for the onset, 50-60 msec for the peak, and 40-90 msec for the ‘duration’. The quantitative analysis of the average temporal dynamics of modulation depth, minimal response and response at orthogonal orientation showed that the timing of growth and decline of the modulation depth was similar between V2 and V1. However, the minimal response and the response to orthogonal orientation in many V2 neurons exhibited complex dynamics that differed considerably from that in V1. These results confirm that in addition to V2 neurons that behave like V1 neurons, V2 contains a population of neurons that exhibit more complex response properties that may reflect different or higher cortical processing.



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