Age-related changes in the visual cortex.

The ability to accurately perceive the speed of moving objects is one of many visual functions that decline with age. One factor that may contribute to this is a deterioration in temporal processing speed. At present, there is a dearth of information concerning how this may occur in the central nervous system, particularly in the visual cortex. Thus, in the present study, we investigated the neural basis of speed and temporal processing in areas 17 and 18 of visual cortex in young and aged rats using either a moving bar of light or a series of flashing lights. Our results showed that the mean preferred speed of a moving bar of light was significantly reduced in aged as compared to young animals. We also found that cells recorded from young animals were able to entrain to a higher frequency of flashing light stimuli than those recorded from aged animals. In addition, we found no age-related differences between cortical fields. These results suggest an age-related difference in temporal processing speed at the level of visual cortex.

Critical flicker frequency responses in visual cortex.

Critical flicker frequency (CFF) threshold is defined as the frequency at which a flickering light is indistinguishable from a steady, non-flickering light. CFF is useful for assessing the temporal characteristics of the visual system. While CFF responses are believed to reflect activity in the central visual system, little is known about how these temporal frequencies are processed in the visual cortex. The current paper estimated the CFF threshold for cells in the rat visual cortex by recording single unit responses to flickering stimuli. Results showed that: (1) there was a broad range of temporal tuning, (2) CFF threshold was lower in simple cells than in complex and hypercomplex cells, and (3) there was no significant difference in CFF threshold between areas 17 and 18.