Functional organization of the corticofugal system from visual cortex to lateral geniculate nucleus in the cat

Abstract

1. In the cat visual cortex (VC), electrophoretic glutamate application at a depth corresponding to layer VI may have excitatory or inhibitory effects on relay cells of the lateral geniculate nucleus (LGN). Corticofugal excitation was seen, if the receptive field centers (RFCs) of the VC neurons recorded at the application site were within 2.3 degrees of the RFCs of the LGN neurons under test. Inhibitory effects were seen if the RFCs of both cells were further apart up to 3.1 degrees. Glutamate application at more superficial cortical sites had no effect on LGN-neuron activity. 2. Cross-correlation analysis between spontaneous activities of simultaneously recorded VC and LGN neurons revealed excitatory cortico-geniculate connections in 18 pairs with RFCs separated by less than 1.7 degrees. In 15 pairs the peak latency of the excitation was 2--5 msec (3.4 msec in the average), 3 pairs showed long cortico-geniculate latencies (13--18 msec). The existence of a fast and slow cortico-geniculate system is suggested. 3. Inhibitory cortico-geniculate interaction was demonstrated with cross-correlation analysis in 8 pairs of which 4 had RFCs separated by more than 1.7 degrees. The onset latency of the inhibition was 2--7 msec except for 2 pairs with about 20 msec latency. 4. Most of the LGN neurons which were affected by cortical glutamate application or which showed an excitatory or inhibitory connection with a VC neurons were sustained cells, while the majority of VC neurons which were recorded in the effective glutamate application sites or which showed a significant interaction with LGN neurons in the cross-correlogram were binocularly driven and complex, with mostly large RFCs (mean diameter 3.5 degrees). They responded briskly to moving small spots as well as to moving slits. 5. It is concluded that the corticofugal excitatory effect is transmitted through monosynaptic links from VC neurons located in layer VI (complex cell) to LGN relay neurons (mostly sustained-cell) and this system is organized in a precise topographical manner. 6. In an Appendix neuron pairs which showed a positive correlation in the geniculo-cortical direction were described. The findings may support the view that complex as well as simple cells are drive monosynaptically from geniculo-cortical afferents of the sustained or transient type.

Corticogeniculate feedback sharpens the temporal precision and spatial resolution of visual signals in the ferret

“…Thus, particular features of a visual scene could trigger CG activation, causing streamspecific feedback activation of LGN ensembles via the circuit mechanism described above. Interestingly, CG feedback in a variety of species is known to operate on different timescales due to differential axon conduction velocities among the diverse CG neuronal types (35,44,(47)(48)(49)(50)(51). The large variation in axon conduction times suggests that different CG neurons may have shorter or longer timescales over which they can integrate incoming information.…”

Feedback from V1 and inhibition from beyond the classical receptive field modulates the responses of neurons in the primate lateral geniculate nucleus

“…It has been known for some time that cortico-geniculate feedback modulates the flow of visual information that reaches the cortex (Hull, 1968;Kalil & Chase, 1970;Singer, 1977;Tsumoto et al, 1978;Marrocco & McClurkin, 1985;Sherman & Koch, 1986;590 B.S. Webb et al Murphy & Sillito, 1987;Marrocco et al, 1996;Cudeiro et al, 2000).…”

“…Physiological studies have found that cortico-geniculate feedback both facilitates and inhibits the relay of retinal information to the cortex (Hull, 1968;Kalil & Chase, 1970;Singer, 1977;Tsumoto et al, 1978;Gulyás et al, 1990;Cudeiro & Sillito, 1996;Marrocco et al, 1996;Wörgötter et al, 1998;Murphy et al, 1999;Cudeiro et al, 2000). Visual properties of LGN neurons can be shaped by cortico-geniculate feedback.…”

Glutamate receptor functions in sensory relay in the thalamus

“…Thus, the level of cortical activity could regulate the sleep-related activity of thalamic neurons via mGlu1 receptor activation (Hughes et al 2002). However, it is also highly likely that there is a contribution from corticofugal systems to sensory responses in vivo, and this has been investigated over many years (Tsumoto et al 1978;Murphy & Sillito 1987;Sillito et al 1994) (and see Sherman & Guillery (2002) and Sillito & Jones (2002)). It has been speculated that the in uence of the cortical input may operate via NMDA receptors or mGlu receptors (Koch 1987;Sherman & Guillery 2000), largely because transmission via these receptor types would allow the non-linear ampli cation of excitatory inputs mediated via, for example, AMPA receptors.…”