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1 Dept. of Neurobiology, Harvard Med Sch, Boston, Massachusetts, United States
* To whom correspondence should be addressed. E-mail: jassad{at}hms.harvard.edu.
The lateral intraparietal area (LIP) of the macaque is believed to play a role in the allocation of attention and the plan to make saccadic eye movements. Many studies have shown that LIP neurons generally encode the static spatial location demarked by the receptive field (RF). Here we examine direction selectivity of LIP neurons. Animals were only required to fixate while motion stimuli appeared in the RF. To avoid spatial confounds, the motion stimuli were patches of randomly arrayed dots that moved with 100% coherence in eight different directions. We found that the majority (61%) of LIP neurons were direction selective. The direction tuning was fairly broad, with a median direction-tuning bandwidth of 136 degrees. The average strength of direction selectivity was weaker in LIP than that of other areas of the dorsal visual stream, but that difference may be due to the fact that LIP neurons showed a tonic offset in firing whenever a visual stimulus was in the RF, independent of direction. Direction-selective neurons do not appear to constitute a functionally distinct subdivision within LIP, since those neurons had robust, sustained delay-period activity during a memory delayed saccade task. The direction selectivity could also not be explained by asymmetries in the spatial RF, in the hypothetical case that the animals attended to slightly different locations depending on the direction of motion in the RF. Our results show that direction selectivity is a distinct attribute of LIP neurons in addition to spatial encoding.
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T. M. Herrington and J. A. Assad Neural Activity in the Middle Temporal Area and Lateral Intraparietal Area during Endogenously Cued Shifts of Attention J. Neurosci., November 11, 2009; 29(45): 14160 - 14176. [Abstract] [Full Text] [PDF] |
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