We propose to continue to investigate the dynamic control of the thalamic relay of retinal information to the cortex and how it is affected by behavioral state and attention. In light of the progress we have made during the last funding period, our aims essentially will be to continue to explore the effects of more complex behaviors on the activity of the LGN relay and to extend these studies to other thalamic nuclei. Over the period of the last grant we have provided evidence that refutes the idea that the LON acts as a mere passive relay of retinal information bound for cortex. We have added to the accumulating body of evidence showing that the LGN dynamically affects the relay of visual sensory information to cortex under the control of descending cortical and ascending brainstem inputs. We have confirmed the findings from studies of non-primate mammals and provided additional evidence that in the awake, behaving monkey the behavioral constraints of the animal dictates the firing level and pattern of LON cells; thus the nature of the information reaching the cortex is controlled. We have shown that the state of consciousness, encompassing wakefulness through to sleep, significantly affects LGN firing by affecting the inactivation state of a voltage sensitive Ca2+ current that, in turn, determines the firing mode-burst or tonic-of relay cells. Other thalamic nuclei appear to be even more significantly affected by state of consciousness than the LGN. We also found that saccadic eye movements increase LGN activity of M (but not P) cells, while it reduces bursting in both. Preliminary experiments in which we trained monkeys to attend to objects in the receptive field (RF) as opposed to non-RF suggest that attention within the RF significantly enhances the activity of some LUN cells. We shall continue our studies by using more complex behavioral paradigms in order to further elucidate the dynamic nature of the thalamic relay. Specifically, we shall look at attentional demands involving detection tasks and its relationship to burst mode activity. We will also look at the interactions between sensory modalities (e.g. auditory and visual) and at the level of bursting across other thalamic nuclei and primary visual cortex. Finally, we note evidence that many visual cortical neurons also can fire in burst mode, which appears to provide especially effective postsynaptic responses, and that this seems to be under modulatory control. Thus we shall explore the possibility that various behavioral and attentional states affects firing mode of cells in primary visual cortex.
| 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 |
| 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 |
| Sherman, S M (2001) Thalamic relay functions. Prog Brain Res 134:51-69 |
