Figure 1.

Behavioral Evidence for the Dominance of Touch-Induced Withdrawal over Feeding

(A) A video sequence of the head and anterior foot region showing feeding and withdrawal responses before and after the application of a touch stimulus. Sucrose is applied throughout the sequence. Feeding movements of the radula (bite) in response to food can be seen in frame 1, but these are inhibited by touch (mouth closed, frames 2 and 3). Touch also induces withdrawal responses in the head-foot region (frame 3). Frame 4 shows the resumption of feeding.

(B) Example of data obtained from the video recordings showing how the rhythmic feeding movements in response to continuous sucrose application are inhibited by a strong touch stimulus. Withdrawal responses are monitored by measuring the change in the relative light intensity caused by the retraction of the anterior head-foot region. The dashed region in the inserted image indicates the fixed sampling area for the measurement. The movement in response to a single touch consists of a rapid retraction, followed by a slower recovery phase when the head-foot returns to its original position. The recovery phase is probably passive because there are no known muscles that could account for this phase of the response. Individual bites that indicate the occurrence of an ingestive feeding cycle are shown as vertical bars in the lower trace.

(C) Six bites occur in the 20 s before touch, and two bites occur in the 20 s after touch. The number of feeding cycles in the 20 s before touch is significantly greater than the number in the 20 s after touch (n = 16; Wilcoxon signed-rank test: W = 136, p < 0.0004. Error bars show ±SEM).