Flutter-Like Response in Visual Cortex of the Semi-Isolated Turtle Brain

activity of nearby receptors in the eye that see an object becomes correlated (5). The lateral eye is highly sensitive to the flickering light from the overhead waves. A large component of the light reflected from grey targets centers at -2-4 Hz which is the peak of the temporal transfer function of the eye (Fig. 1B; 6, 7, 8). Phototransduction mechanisms set the underlying shape of the transfer function, which two inhibitory processes then sharpen and amplify (6, 7). As a result, the power spectrum of the spike train recorded from receptors viewing the grey target grows considerably in the range of 2-4 Hz (Fig. 1 B). In this paper we show that a consideration of the natural environment of an animal can lead to a better understanding of its visual system. The Limulus eye appears to be adapted to a particular feature of its environment-the flickering light reflected off the carapace of a potential mate. These light signals help males detect a female irrespective of the contrast of her carapace. Frequency tuning of vision is not unique to horseshoe crabs and has been observed in many animals, such as cats (9) and humans (10). Perhaps their lighting environment also deserves a closer look. Supported by NSF grant BNS9309539 and NIH grants MH4974 1 and EY00667.