Friday, June 29, 2007

Recent progress in wet color perception research

The June 15 issue of Science has tow very interesting papers describing new results in perception. Both group of researchers studied the synchronization of gamma waves to investigate how various regions of the brain communicate. Their research indicates that top-down signals between brain regions regulate the flow of information, and that a distributed neural networks that use oscillatory dynamics support a broad spectrum of neural processing and behavior.

You may want to start by reading the introductory overview article Neural Networks Debunk Phrenology, by Robert T. Knight on page 1578. You may want to read second the earlier related paper Top-Down Versus Bottom-Up Control of Attention in the Prefrontal and Posterior Parietal Cortices, by Timothy J. Buschman and Earl K. Miller that was published in the 30 March issue on p. 1860.

In Modulation of Neuronal Interactions Through Neuronal Synchronization, Thilo Womelsdorf, Jan-Mathijs Schoffelen, Robert Oostenveld, Wolf Singer, Robert Desimone, Andreas K. Engel, and Pascal Fries recorded multiunit activity and local field potentials simultaneously from four to eight electrodes while the neurons were visually stimulated with moving gratings. They tested the hypothesis that the phase relation between the rhythmic activity of groups of neurons determines the strength of their mutual influence and found a heavy dependence of the correlation on phase. These results suggest a mechanism by which signals are matched and coupled during complex perceptual and cognitive operations. The fact that in the V4 area the synchrony occurs at 60 Hz, which is higher than the frequency ranges for the various attention functions, color identification is relatively effortless.

In Neural Mechanisms of Visual Attention: How Top-Down Feedback Highlights Relevant Locations, Yuri B. Saalmann, Ivan N. Pigarev, and Trichur R. Vidyasagar simultaneously recorded from two areas in the dorsal stream of the visual pathway, the posterior the lateral intraparietal area (LIP, which is critical for spatial attention) in the parietal cortex and the medial temporal area (MT, which plays a role in the perception of motion), while subjects performed a delayed match-to-sample memory task. Activity in LIP predicted activity in MT when the receptive fields of the LIP and MT neurons were in the same place and when the monkey was attending to that place. LIP feedback can thus account for attention-enhanced MT responses, in simpler words, parietal neurons may thus selectively increase activity in earlier sensory areas to enable focused spatial attention.