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This Article Full Text Full Text (PDF) All Versions of this Article: 101/1/289    most recent 00400.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Fanini, A. Articles by Assad, J. A. Search for Related Content PubMed PubMed Citation Articles by Fanini, A. Articles by Assad, J. A.

Direction Selectivity of Neurons in the Macaque Lateral Intraparietal Area

Department of Neurobiology, Harvard Medical School, Boston, Massachusetts

Submitted 9 April 2007; accepted in final form 1 November 2008

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). LIP neurons might also provide information about the features of visual stimuli within the RF. For example, LIP receives input from cortical areas in the dorsal visual pathway that contain many direction-selective neurons. 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°. 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 because of 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 seem to constitute a functionally distinct subdivision within LIP, because 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.