Sequential change in receptive fields of striate neurons in dark adapted cats

Summary

• 1. A general purpose, digital computer was employed to map quantitatively the receptive fields of units in cat's striate cortex.

• 2. Receptive fields were studied as a function of barbiturate anesthetic level under dark adapted conditions.

• 3. Receptive fields obtained from lateral geniculate axons were topographically simple and usually represented a single peak with concentric zones of decreasing excitability. Such fields were stable under all anesthetic and electroencephalographic conditions.

• 4. Responses were recorded from striate cells, both simple and complex in the sense of Hubel and Wiesel. These demonstrated varied field configurations such as an excitatory cylinder in an inhibitory field, excitatory vertical axis flanked by asymmetric inhibitory areas, and more complex patterns including potentially direction and velocity sensitive ones.

• 5. Many cortical maps were unstable over time, especially in the presence of low voltage, fast electroencephalographic activity. Changes were not random nor did they represent simple linear displacements of peaks, but included axis shifts, gradient change, and expansion or contraction of excitatory and inhibitory zones with centers at fixed relative positions.

• 6. Heavy barbiturate anesthesia and spontaneous spindling in the EEG markedly reduced the variability in these maps; the encephale isole preparation was more stable than spinally intact animals. This association suggests a role of the midbrain reticular formation in cortical variability.

• 7. Random rather than iterative presentation of matrix points resulted in higher mean firing rates and more stable receptive fields, probably the result of photochemical recovery in dispersed receptors and time averaging of cellular excitability.

• 8. When stability was analyzed as a function of time interval of response (early on, late on, early off, late off), initial on responses were often more stable than longer latency late on- or off-responses. This factor, among others discussed, makes eye movement an unlikely explanation for map variability. It suggests additionally that late on- and off- responses represent input to the cortical cell from units other than those producing the early on-response.

• 9. The effects of pentobarbital, in addition to stabilization of the receptive field, included striking phase reversals in which inhibitory regions became excitatory and visa versa. Firing rate often changed substantially, but both increases and decreases were observed.

• 10. It is argued that visual response under pentobarbital is a special and not the general case of visual perception and that sequential receptive field changes during aroused brain states reflect integrative, purposive processes at the cortical level.