Visual response latencies of magnocellular and parvocellular LGN neurons in macaque monkeys

Abstract

Signals relayed through the magnocellular layers of the LGN travel on axons with faster conduction speeds than those relayed through the parvocellular layers. As a result, magnocellular signals might reach cerebral cortex appreciably before parvocellular signals. The relative speed of these two channels cannot be accurately predicted based solely on axon conduction speeds, however. Other factors, such as different degrees of convergence in the magnocellular and parvocellular channels and the retinal circuits that feed them, can affect the time it takes for magnocellular and parvocellular signals to activate cortical neurons. We have investigated the relative timing of visual responses mediated by the magnocellular and parvocellular channels. We recorded individually from 78 magnocellular and 80 parvocellular neurons in the LGN of two anesthetized monkeys. Visual response latencies were measured for small spots of light of various intensities. Over a wide range of stimulus intensities the fastest magnocellular response latencies preceded the fastest parvocellular response latencies by about 10 ms. Because parvocellular neurons are far more numerous than magnocellular neurons, convergence in cortex could reduce the magnocellular advantage by allowing parvocellular signals to generate detectable responses sooner than expected based on the responses of individual parvocellular neurons. An analysis based on a simple model using neurophysiological data collected from the LGN shows that convergence in cortex could eliminate or reverse the magnocellular advantage. This observation calls into question inferences that have been made about ordinal relationships of neurons based on timing of responses.

Fine Temporal Properties of Center–Surround Interactions in Motion Revealed by Reverse Correlation

“…3A, arrows), and duration of influence all showed a systematic dependence on surround contrast: the temporal profile of surround influence was longer, started earlier, and peaked earlier as the surround contrast was decreased. These results may be a result of longer and more variable neural response latencies at low contrast (Lennie, 1981;Maunsell et al, 1999;Reich et al, 2001).…”

“…In addition to the peak shift, we also observed broadening of temporal influence functions for low-contrast surrounds. This result may be explained by increased variability in the latency of low-contrast stimuli (Maunsell et al, 1999). Specifically, the increased range of surround latencies at low contrast extends the range of time points within which surround motion can occur and still interact with the center motion.…”

“…The longer neural latency associated with weaker visual stimuli (Maunsell et al, 1999;Reich et al, 2001) may explain differences in the start and peak time of the temporal profile for different contrast surrounds (Fig. 3A, Table 1).…”

“…We then investigated whether the discriminability of center motion is influenced by surround motions occurring at different times relative to the center stimulus. Of particular interest was whether the timing of the influence of the surround changes with stimulus contrast, a question motivated by the known contrast-dependency of neuronal latencies (Lennie, 1981;Maunsell and Gibson, 1992;Maunsell et al, 1999;Reich et al, 2001). …”

Attention model of binocular rivalry

“…After stimulus offset, a decay was modeled by a hyperbolic tangent function with a half-life of 15 ms. The onset transient and the offset decay captured the delay and the time course of the responses of subcortical neurons (29,30).…”