H1111111

Interval (hr)

FIGURE 3.4 Intervals near the circadian range (unfilled circles) are characterized by lower variability than intervals outside this range (filled squares). Variability in anticipating a meal was measured as the width of the response distribution prior to the meal at 70% of the maximum rate, expressed as a percentage of the interval. The interval is the time between light offset and meal onset in a 12-12 light-dark cycle (leftmost two squares) or the intermeal interval in constant darkness (all other data). The percentage width was lower in the circadian range than outside this range, F(1, 20) = 22.65, P < .001. The width/interval did not differ within the circadian, F(4, 12) = 1, or noncircadian, F(3, 8) < 1, ranges. The same conclusions were reached when the width was measured as 25, 50, and 75% of the maximum rate. (From Crystal, J.D., J. Exp. Psychol. Anim. Behav. Process., 27, 68-78, 2001a. Copyright © 2001 by the American Psychological Association. Reprinted with permission.)

less than 24 h, as shown in Figure 3.6. For example, behaviors that are instrumental in producing food (e.g., approaching the food source or pressing a lever) precede meal availability for intermeal intervals outside this limited range (see Figure 3.5 for 14 h (Crystal, 2001a); see Figure 3.6 for a reanalysis of 18 and 19 h (Bolles and Stokes, 1965; Boulos et al., 1980)). The temporal functions for intervals below the circadian range are less steep and have lower terminal response rates than intervals in the circadian range (see Figure 3.6). These features are characteristic of relatively high variability (i.e., low sensitivity to time), which is consistent with the data illustrated in Figure 3.4 (Crystal, 2001a). In contrast, wheel-running activity does not precede meals at these intervals (Bolles and de Lorge, 1962; Bolles and Stokes, 1965; Mistlberger and Marchant, 1995; Stephan et al., 1979a; White and Timberlake, 1999). Behaviors that are instrumental in producing food may be a more sensitive measure of food anticipation than general activity measures for intervals below the circadian range. Behaviors that serve to produce food may be expected

FIGURE 3.5 Activity records for a randomly selected rat from 14-h intermeal intervals showing robust anticipation of 14-h intermeal intervals plotted as a function of days (left panel) and meal intervals (middle panel). Meals (indicated by rectangles) were preceded by a burst of anticipatory responses in constant darkness. Right panel shows mean response rate functions for each individual rat with a 14-h intermeal interval. Data were examined in 10-min bins. If the response rate was greater than one response per minute in the bin, then a vertical deflection was placed on the activity record (left and middle panels). A burst of these anticipatory responses (quantified as at least 4 of 6 bins with responses) occurred in the hour before 70% of the last 10 meals; a lower level of anticipation (16%) was observed 4 h before the meal, P < .001. (From Crystal, J.D., J. Exp. Psychol. Anim. Behav. Process, 27, 68-78, 2001a. Copyright © 2001 by the American Psychological Association. Reprinted with permission.)

FIGURE 3.5 Activity records for a randomly selected rat from 14-h intermeal intervals showing robust anticipation of 14-h intermeal intervals plotted as a function of days (left panel) and meal intervals (middle panel). Meals (indicated by rectangles) were preceded by a burst of anticipatory responses in constant darkness. Right panel shows mean response rate functions for each individual rat with a 14-h intermeal interval. Data were examined in 10-min bins. If the response rate was greater than one response per minute in the bin, then a vertical deflection was placed on the activity record (left and middle panels). A burst of these anticipatory responses (quantified as at least 4 of 6 bins with responses) occurred in the hour before 70% of the last 10 meals; a lower level of anticipation (16%) was observed 4 h before the meal, P < .001. (From Crystal, J.D., J. Exp. Psychol. Anim. Behav. Process, 27, 68-78, 2001a. Copyright © 2001 by the American Psychological Association. Reprinted with permission.)

to be particularly relevant in food entrainment from a functional perspective (Tim-berlake, 1993, 1994).

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