Development of Response Timing and Direction Selectivity in Cat Visual Thalamus and Cortex

Abstract

Single-unit recordings were made in the dorsal lateral geniculate nucleus (LGN) and visual cortex of kittens that were 4-13 weeks of age. Responses to visual stimuli were analyzed to determine the relationship between two related facets of the behaviors of the cells: direction selectivity (DS) and timing. DS depends on timing differences within the receptive field. Cortical DS was present at all ages, but its temporal frequency tuning changed. In kittens, DS was more common at high (approximately 4 Hz) than low ( approximately 1 Hz) temporal frequencies. This is in contrast to adults, in which DS is tuned to low frequencies, more common at 1 Hz than at 4 Hz (Saul and Humphrey, 1992a). In adult cats, the LGN provides the cortex with a wide range of timings that are also observable in cortical receptive fields (Saul and Humphrey, 1990, 1992b; Alonso et al., 2001). In kittens, LGN and cortical timing were immature. Most cells showed long-latency sustained responses. At low temporal frequencies, the variance in timing was small, but at higher frequencies, all timings were well represented. The timing data thus matched the temporal frequency tuning of DS. Kittens show DS at high temporal frequencies because of the abundance of inputs with different timing at high frequencies. As cells in the LGN mature, more low-frequency timing differences become available to the cortex, allowing DS at low frequencies to become possible for more cortical cells.

The Sparseness of Neuronal Responses in Ferret Primary Visual Cortex

“…It is difficult to see how first-spike latency could be a reliable encoder, unless many neurons of like spatiotemporal character signal in parallel. Furthermore, when considering how our whole disparate population of neurons might encode natural scenes, the response latency of different neurons varied widely (by 30 ms or more), as found for other visual stimuli (Troy and Lennie, 1987;Maunsell et al, 1999;Saul and Feidler, 2002;Weng et al, 2005). Differences between neurons were far greater than any subtle intrastimulus differences within the responses of a single neuron.…”

Cross-Orientation Suppression: Monoptic and Dichoptic Mechanisms Are Different

“…This mechanism is an ideal substrate for monoptic COS because it can explain the main characteristics of COS, i.e., suppression is not tuned to orientation (Bonds 1989;DeAngelis et al 1992;Morrone et al 1982), is broadly tuned for spatial frequency (Bonds 1989;DeAngelis et al 1992;Morrone et al 1982), occurs at very high temporal frequencies (Allison et al 2001;Freeman et al 2002), and is immune to prolonged adaptation (Freeman et al 2002). The transformation from LGN to cortical response properties is masked by a low-pass filtering of temporal frequency sensitivity (Hawken et al 1996;Saul and Feidler 2002) and the emergence of contrast adaptation (Ohzawa et al 1985). It is interesting to note that the mechanism underlying monoptic COS might actually be the cause of these changes.…”

Lagged Cells

“…A delayed emergence of inhibition might explain the development of both transient (late inhibition) and lagged (early inhibition) cells. The development of timing correlates with the development of the temporal frequency tuning of direction selectivity [16] . As first noted by Hubel and Wiesel [45] , direction selectivity is present at eye-opening.…”

“…Sustained responses correspond to monophasic, and transient responses to biphasic impulse responses. Nonlagged impulse responses are dominated by the initial phase, lagged by the second phase: the initial phase is inhibitory in lagged cells [14][15][16] , whereas the second phase is inhibitory in nonlagged cells.…”