Abstract: DESCRIPTION (provided by applicant):
The pulvinar nucleus of the thalamus is one of the most enigmatic structures in the brain. Of thalamic nuclei, it shows the largest increase in size with evolution, keeping pace with the size of primate neocortex. Despite considerable effort, its function remains essentially completely unknown. Two related suggestions dominate current thinking about the pulvinar, and each has some experimental support. Neither, however, has been critically tested, and the present application is intended to provide this critical test of both ideas. The first idea is that the pulvinar controls the spatial location of directed attention. This idea has support - though not conclusive - from lesion studies and physiological recording studies. We plan to directly test this idea by perturbing activity in the pulvinar while recording in extrastriate cortex. We know that directed attention produces local changes in the gain of response of extrastriate neurons; activation of the pulvinar should mimic this change and reversible inactivation of the pulvinar should eliminate it. The other suggestion for the role of the pulvinar concerns the mechanism of such gain changes in sensory cortex. In particular, it has been suggested that recurrent projections between the pulvinar and cortical structures control the flow of information between cortical areas; this regulation might underlie any role in directing spatial attention. We plan to test this idea using multiple electrode recording in extrastriate cortex. Two dorsal extrastriate areas, the middle temporal (MT) and the medial superior temporal (MST) are both connected to the same subdivision of the pulvinar (Plm), and also connected with each other - MT provides a dominant source of feedforward input to MST. We will record from both structures simultaneously while again perturbing the activity in the pulvinar. If the connections with the pulvinar regulate information flow in visual cortex, we predict that such perturbation will modulate the cross-correlation of activity between MT and MST. Success on either aim will dramatically influence our thinking about the function of thalamocortical circuits

Thesaurus Terms:
attention, brain electrical activity, brain mapping, neuropsychology, pulvinar thalami, visual perception action potential, cue, electrostimulus, neural information processing, neural transmission, temporal lobe /cortex, visual cortex, visual feedback Macaca mulatta, behavioral /social science research tag, electrode
 
Institution: UNIVERSITY OF CALIFORNIA DAVIS
OFFICE OF RESEARCH - SPONSORED PROGRAMS
DAVIS, CA 95618
Fiscal Year: 2006
Department: CENTER FOR NEUROSCIENCE
Project Start: 01-APR-1995
Project End: 31-MAR-2008
ICD: NATIONAL EYE INSTITUTE
IRG: ZEY1

J Neurophysiol 88: 3469-3476, 2002; doi:10.1152/jn.00276.2002
0022-3077/02 $5.00
J Neurophysiol (December 1, 2002);10.1152/jn.00276.2002
Submitted on 2 April 2002 Accepted on 13 August 2002

Motion Adaptation in Area MT
 
Richard J. A. Van Wezel and Kenneth H. Britten
University of California, Davis Center for Neuroscience and Section of Neurobiology, Physiology, and Behavior, Davis, California 95616

Preparation and recordings
We recorded single MT cells in three adult female rhesus monkeys (Macaca mulatta). Before recording, each monkey had been trained to fixate a stationary red spot of 0.23° diam in the presence of visual stimuli. The animal's fluid intake was restricted, and behavioral control was achieved using operant conditioning techniques. The animal received a fluid reward (a drop of water or juice) for keeping its eyes within a window (1-2.5° width) surrounding the fixation point for the duration of the trial.

All surgical and experimental methods followed previously described procedures (Britten et al. 1992 ), conformed to the National Institutes of Health Guide for the Care and Use of Laboratory Animals, and were approved by the UC Davis Animal Care and Use Committee.

Under deep surgical anesthesia, each animal was implanted with a scleral search coil (Judge et al. 1980 ) and was equipped with a stainless steel head restraint post and recording cylinder (Crist Instrument, Damascus, MD) located over the occipital cortex. The monkeys were given at least 2 weeks to recover from surgery before recording.

A plastic grid secured inside the cylinder provided a coordinate system of guide tube support holes at 1-mm intervals (Crist et al. 1988 ). Guide tubes were inserted transdurally through these holes, with local anesthetic if necessary. Parylene-insulated tungsten microelectrodes (MicroProbe, Potomac, MD) were inserted through these guide tubes, and neural signals from these electrodes were amplified, filtered, and displayed by standard methods.

Spikes were isolated using a time-amplitude window discriminator (Bak Electronics, Germantown, MD) and converted to voltage pulses that were fed to the computer controlling the experiment. Data acquisition and experimental control were managed by the software package REX (Hays et al. 1982 ). Neurons were determined to be located in MT by physiological criteria: receptive field size, directionally selective responses, columnar organization for preferred directions, and appropriate retinotopic organization (Albright et al. 1984 ; Maunsell and Van Essen 1983b ; Zeki 1974 ).

In two monkeys, we verified histologically that the recording region corresponded to the heavily myelinated zone on the posterior bank of the superior temporal sulcus (STS). This landmark is a very reliable indicator of the location of MT (Desimone and Ungerleider 1986 ; Maunsell and Van Essen 1983a ). This verification is not yet available for the third monkey because it is currently involved in other experiments.
 
Once a single unit was isolated, the receptive field was mapped using hand-controlled stimuli, typically moving bars of light. We only included in our analysis cells that were fully directionally selective, by which we mean that there is no overlap in the response distributions for the preferred and null directions at the highest coherence tested (Britten et al. 1992 ).

This criterion need not imply a DSI [the standard index of directionality, calculated as (pref null)/(pref + null)] near 1.0, nor that the cells be silent in their null direction. Thirteen of 87 cells did not meet this criterion.

We imposed this criterion only for consistency with previous work, but inspection of the excluded cells' data showed that the adaptation effects were very similar as that from the retained cells (data not shown).