20 Hz Bursts of Activity in the Cortico-Thalamic Pathway During Attentive Perception
It is well established that thalamo-cortical fibers of the visual pathway of the cat send out collaterals to two recurrent loops: inhibitory, via GABAergic interneurons of the perigeniculate nucleus (PGN) and excitatory, relayed by the pyramidal cells of layer 6 of the striate cortex. Both of these loops terminate on principal cells of lateral geniculate nucleus (LGN). There are data indicating the possible role of PGN neurons in synchronization of thalamo-cortical rhythmic activity (see Steriade and Llinas, 1988 for a review), whereas hypotheses concerning the functions of the cortico-geniculate pathway lack clear experimental support. This pathway should be important in view of the fact that cortical axons outnumber all other excitatory inputs to LGN principal cells (Wilson et al., 1984). One of the main reasons for the lack of understanding of the role of cortical input may be the poor responsiveness of layer 6 pyramidal cells in anaesthetized cats. This was demonstrated by Livingstone and Hubel (1981) who showed further that when layer 6 cells become active, after the cat recovered from the anaesthesia, also their specific responses to visual stimuli were noticeably enhanced. These effects were also accompanied by more vigorous responses of LGN principal cells to specific stimulation.
KeywordsCage Tungsten Assure Peri Azimuth
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