1985 — 2003 |
Malpeli, Joseph G |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Thalamic Control of Cortical Visual Processing @ University of Illinois Urbana-Champaign
The long-term objective of this project is to understand how afferent parallel channels contribute to the processing of visual information in cerebral cortex. The output of the retina is organized into at least three channels (W, X and Y cells), which are relayed through the lateral geniculate nucleus (LGN) to the visual cortex. The LGN is a laminated structure, and the pattern of lamination varies greatly among species. In the cat, three retinal channels are distributed among nine layers of the LGN complex, creating at the morphological level of organization several additional afferent channels. Many individual cells in cortex receive convergent inputs from multiple channels through both feedforward and feedback pathways. Cortex and other central structures project heavily to the LGN, and therefore are capable of strongly regulating LGN transmission to cortex. The complex interactions of afferent channels, intracortical circuits, and central feedback to the LGN are probably dynamically regulated in accordance with the perceptual demands and behavioral state of the animal. Examining these circuits in the awake, behaving animal is critical for insights into their functional roles. Three aspects of these interactions will be examined in awake cats trained in visuomotor tasks. Cells in the LGN will be recorded to investigate the effects of saccades, gaze angle, and spatially-selective attention on their activity, and to determine how these effects vary by layer and by cell type. The activity of corticogeniculate cells in primary visual cortex will be examined under the same behavioral circumstances to identify dynamic changes that are common to or different from those observed in LGN cells. In order to understand the contributions of individual LGN layers to dynamic changes in cortex, layers will be selectively inactivated with microinjections of blocking agents while visuomotor behavior and cortical activity are observed. To gain insights into the origins of interspecies variations in LGN laminar structure, the morphogenesis of the monkey LGN will be model led with simulated annealing techniques. The aim is to test the hypotheses that in the rhesus monkey, eccentricity-related variations in the number of layers are promoted by regional variations in retinal ganglion cell density, and that the blind spot determines the point at which the pattern changes by serving as a "seed crystal", causing an abrupt change in the anterior-posterior free-energy gradient that determines the most stable state.
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2004 — 2007 |
Malpeli, Joseph G |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Role of Parabigeminal Neucleus in Visuomotor Behavior @ University of Illinois Urbana-Champaign
[unreadable] DESCRIPTION (provided by applicant): Good vision requires an oculomotor system that can make rapid and accurate eye movements, called saccades, to visual targets of interest. To do this, the brain must have an internal representation of target location. The superior colliculus (SC), the main source of saccade commands to brainstem circuits driving the eyes, encodes target localization and saccade metrics by place codes: a retinotopic map of locations in register with a map of saccade vectors. It appears that the parabigeminal nucleus (PBN), a small cluster of cells on the lateral edge of the midbrain that is reciprocally interconnected with the SC, also encodes target location, but by a rate code. When cats visually track a moving object, they rely primarily on a series of catch-up saccades to continually intercept it. Preliminary studies have revealed that in the intervals between catch-up saccades, PBN cells fire at rates proportional to the distance between the eye and potential target, or retinal position error (RPE). During saccades, PBN activity abruptly changes to levels appropriate to RPE at saccade end in a fashion that seems too fast for visual feedback, suggesting that activity may be reset by an internally generated signal, such as a resettable integrator of eye velocity, or an open-loop feedforward signal. Its robust anatomical interconnections with the SC imply that the PBN primarily contributes to the saccade system by providing continuous information on target location during intersaccade intervals. Whether or not it contributes to the dynamics or metrics of the saccade is unknown. Since the SC place code must at some point be translated into a rate code to drive eye movements, the PBN may provide a useful model for understanding how a place-to-rate code translation can be accomplished. The goals of this project include better defining the range and topography of RPE encoding, determining if PBN activity provides an index of the currently attended saccade target, examining PBN interactions with the SC, investigating the nature of the signal that resets PBN activity during saccades, and examining the role of the PBN in predictive tracking of moving targets. Historically, there has been a productive interaction between oculomotor physiology and clinical neurology. The PBN appears to be an important part of the oculomotor system, and its incorporation into models of oculomotor circuits will extend this valuable interchange. [unreadable] [unreadable]
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