(investigator's): We propose to study effects of differing behaviors on the relay of retinal information through the lateral geniculate nucleus (LGN) to cortex. Considerable recent evidence at the cellular and circuit levels from non-primate mammals has made it clear that the LGN is not a simple, machine-like relay. Rather, based on anatomical and cellular evidence, it seems clear that the nature and extent of retinal information reaching cortex for further processing is dynamically controlled at the thalamic level. The vast majority(80-90 percent) of synaptic input onto geniculate relay cells is nonretinal; these inputs serve to control a number of important voltage-gated properties of the relay cells, and the activation state of these properties significantly affects how relay cells will respond to retinal inputs. This has led to a number of testable hypotheses that requires a behaving physiological preparation to evaluate. We have thus selected to study the macaque monkey. Despite the wealth of information available from other visual areas in the behaving monkey, the LGN has been largely neglected. Our primary goal is to determine the effects of various behaviors on response properties of single LGN neurons recorded extracellularly. We shall use a conventional preparation with chronically implanted devices for recording and to monitor eye movements. Behaviors will include the following: I) various stages from fully alert to deep sleep as determined by EEG recording; 2) different eye movements, including smooth pursuit, eccentric fixation, and remembered saccades, the saccades directed into and away from the LGN cell's receptive field; and 3) saccades directed to suddenly varying targets in and away from the receptive field, using both auditory and visual targets to trigger the saccade. During the various behaviors, we shall monitor LGN responses to visual stimulation, including response amplitude, linearity, and spontaneous activity. We shall also construct receiver operating characteristic curves from the responses to evaluate variations in signal detectability during various behaviors. Also, perhaps the most important voltage-dependent property of thalamic relay cells is the low threshold spike (due to a voltage-gated Ca'+ conductance): when triggered, the cell firing is very bursty with clusters of spikes separated by silent periods; and when inactive, the cell responds tonically with single spikes. With either firing mode, the LGN cell responds well to visual stimuli, but the nature of the response is quite different. We shall thus determine the effects of the various behaviors on response type (i e., bursting or not). In addition to the recording, we shall embark on anatomical experiments to characterize the nonretinal pathways into the monkey's LGN.
| Guillery, R W; Sherman, S Murray (2002) Thalamic relay functions and their role in corticocortical communication: generalizations from the visual system. Neuron 33:163-75 |
| Sherman, S M (2001) Thalamic relay functions. Prog Brain Res 134:51-69 |
| Ramcharan, E J; Gnadt, J W; Sherman, S M (2001) The effects of saccadic eye movements on the activity of geniculate relay neurons in the monkey. Vis Neurosci 18:253-8 |
| Levitt, J B; Schumer, R A; Sherman, S M et al. (2001) Visual response properties of neurons in the LGN of normally reared and visually deprived macaque monkeys. J Neurophysiol 85:2111-29 |
