The brain processes time by comparing different cells' response modulations. During development, some of the mechanisms underlying temporal processing mature. It appears from the work of Tallal that disruptions in this maturation can lead to profound deficits in temporal processing abilities in children who are often diagnosed as learning impaired. We are investigating the normal development of response timing in the thalamocortical pathway of cats. Here we show some of the data from the lateral geniculate nucleus (LGN).
Daniels et al. [J. Neurophysiology 41:1373-1393, 1978] reported that latencies of single LGN cells decrease during development. They noted that some A layer cells in young kittens responded to both bright and dark stimuli, as opposed to adult A-layer neurons that are strictly ON- or OFF-center. Stark and Dubin [Vision Research 26:409-414, 1986] challenged this assertion, arguing that no short-latency ON/OFF cells are observed even in very young kittens.
Cai et al. (J. Neurophysiology 78: 1045-1061, 1997) investigated the development of timing in cat LGN. Their data indicated that a decrease in latency occurs after 8 weeks of age.
Saul and Humphrey (J. Neurophysiology 64:206-224, 1990; Visual Neuroscience. 8:365-372, 1992; J. Neurophysiology 68:1190-1208, 1992) provided evidence that cortical direction selectivity at low temporal frequencies arises via timing differences between LGN afferents. Given the large change in timing during development, how do cortical cells maintain their direction selectivity?
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Date created: November 5, 1997 Last modified: November 5, 1997 Copyright © 1997, Alan Saul Maintained by: Alan Saul Alan Saul