Development of orientation preference in the mammalian visual cortex

Abstract

Recent experiments have studied the development of orientation selectivity in normal animals, visually deprived animals, and animals where patterns of neuronal activity have been altered. Results of these experiments indicate that orientation tuning appears very early in development, and that normal patterns of activity are necessary for its normal development. Visual experience is not needed for early development of orientation, but is crucial for maintaining orientation selectivity. Neuronal activity and vision thus seem to play similar roles in the development of orientation selectivity as they do in the development of eye-specific segregation in the visual system.

Figure 1

Development of orientation maps revealed by chronic optical imaging. Single-condition orientation maps at four different ages in one animal. Each row of the figure shows orientation maps recorded in the left primary visual cortex of one ferret at the age [postnatal day (p)] indicated at the left of the row. Each column of single-condition maps shows orientation maps recorded in response to a particular orientation of a moving square wave grating (0° = horizontal). For each map, caudal is up and medial is to the left. The curve in the upper left corner of each map indicates the location of the caudal pole of the cortex behind which the skull remained intact over the cerebellum. In this example, the first clear orientation maps can be seen at postnatal day 38. Individual iso-orientation domains remain stable over time and do not change their position, shape, or size. Scale bar = 2 mm.

Figure 2

Comparison of the development of orientation tuning assessed by optical imaging and electrophysiology. Orientation tuning assessed electrophysiologically from single-unit recordings compared with optical imaging of the development of orientation tuning. Optical imaging data from Chapman et al. (1996) (crosses); single-unit data from Chapman and Stryker (1993) (diamonds). The orientation selectivity index for electrophysiological data is calculated from the Fourier transform of the orientation tuning histogram recorded for each neuron. It equals the amplitude of the second harmonic component normalized by dividing by the sum of the DC level and the amplitude of the second harmonic component and multiplying by 100. The orientation tuning for the optical imaging data is the median length of the vectors in the polar maps. The solid curve indicates the best-sigmoid-fit curve through electrophysiological data, while the dashed curve is the best-sigmoid fit from the optical imaging data. The mean of the best-fit sigmoid for the electrophysiological data is 4 days earlier (P33.4) than the mean for the optical imaging data (P37.4).

Figure 3

Cumulative histogram showing orientation selectivity index distributions for normal immature ferrets (postnatal week 4; n = 4 animals), normal mature ferrets (postnatal week 7 through adult; n = 16 animals), and binocularly deprived ferrets (lid sutured from before the time of natural eye opening through recording sessions on P55, P56, P66, P87, P88, and P90; n = 6 animals). The three distributions are statistically distinct; Mann–Whitney U test, p < .001). Data are from Chapman and Stryker (1993).