Doug Nitz
UC San Diego, Dept. of Cognitive Science
“Parietal cortex and the mapping of space”
Abstract
Recent work examining the spatial firing correlates of posterior parietal cortex neurons indicate that: 1) posterior parietal cortex can map position within an arbitrary frame of reference; 2) mappings in posterior parietal cortex are not necessarily fixed, but responsive to changes in the rules for task performance; and 3) parietal cortex is implicated in processes of mental rotation and imagination of a novel scene. I will cover the literature forming the basis of these claims, make comparisons to work examining hippocampal-based mappings of allocentric (world-centered) space, and consider the problem of deriving positional mappings in arbitrary reference frames from mappings in egocentric reference frames.
Required reading
1) Nitz, D. A. (2006). Tracking route progression in the posterior parietal cortex. Neuron, 49(5):747-756. [pdf]
2) Brozovic, M., Gail, A., and Andersen, R. A. (2007). Gain mechanisms for contextually guided visuomotor transformations. J. Neurosci., 27(39):10588-10596. [pdf]
Comments (3)
mg said
at 6:29 pm on Dec 6, 2008
I originally found it very strange that parietal neurons encode for extended, irregular, and discontinuous portions of routes, but his hypothesis that these cells might be encoding behaviorally epochs, perhaps even with anticipation, as the rat thinking ahead to the next corner, makes a certain degree of sense. I look forward to further arguments in this direction.
Leo Trottier said
at 1:54 pm on Dec 9, 2008
I still wonder how/why it would be adaptive to divide behavior in such kinds of regular epochs, when movement in nature is usually rather idiosyncratic. I can see one more possible explanation, beyond the abstraction of going "up" and "down" a tree: could these epochs be used to encode how to retrace one's steps?
Another alternative explanation is that such epochs, of course, are not unique to spatial navigation and behavior, and instead represent parts of any regular behavior sequence. If this is the case, it should be possible to observe parahippocampal activity as a function of time between epochs ...
Mitch Herschbach said
at 3:47 pm on Dec 10, 2008
I thought it was really interesting that Doug's study of the parietal cortex started as a study of sleep deprivation. Like he said, it calls into question how "theory-driven" experiments must be. Neuroscientific methods seem especially prone for unexpected results like this--e.g., the discovery of mirror neurons was like this. I wonder, however, how much this translates across different methodologies. For example, are behavioral methods going to lead to an unexpected result about a totally distinct phenomenon?
It was bit hard to follow Doug's talk given the lack of slides, but I wonder how what he said about the posterior parietal cortex relates to say Tim McNamara's account of this area as an subsystem for steering and path integration using egocentric reference frames. Doug's study shows posterior parietal can encode route-centered reference frames, and talked about evidence for object-centered reference frames. Have we been too coarse-grained in talking about this brain region and its cognitive functions, such that different subregions perform different functions? Or are there substantive disagreements about the kinds of representations encoded in this region?
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