sensory-specific satiety is intact in amnesics who eat multiple meals

Sensory-Specific Satiety Is Intact in Amnesics Who Eat Multiple MealsAuthor(s): Suzanne Higgs, Amy C. Williamson, Pia Rotshtein and Glyn W. HumphreysSource: Psychological Science, Vol. 19, No. 7 (Jul., 2008), pp. 623-628Published by: Sage Publications, Inc. on behalf of the Association for Psychological ScienceStable URL: http://www.jstor.org/stable/40064965 .

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Sensory-Specific Satiety Is Intact in Amnesics Who Eat Multiple Meals Suzanne Higgs, Amy C. Williamson, Pia Rotshtein, and Glyn W. Humphreys

University of Birmingham

PSYCHOLOGICAL SCIENCE

Research Report

ABSTRACT - What is the relationship between memory and appetite? We explored this question by examining prefer- ences for recently consumed food in patients with amnesia. Although the patients were unable to remember having eaten, and were inclined to eat multiple meals, we found that sensory-specific satiety was intact in these patients. The data suggest that sensory-specific satiety can occur in the absence of explicit memory for having eaten and that impaired sensory-specific satiety does not underlie the phenomenon of multiple-meal eating in amnesia. Overeating in amnesia may be due to disruption of learned control by physiological aftereffects of a recent meal or to problems utilizing internal cues relating to nutritional state.

Reports that amnesic patients eat multiple meals suggest that memory for recent eating may be one factor controlling food intake (Hebben, Corkin, Eichenbaum, & Shedlack, 1985; Rozin, Dow, Moscovitch, & Rajaram, 1998). In addition to exhibiting anterograde amnesia due to bilateral hippocampal damage, the neuropsychological patient H.M. reported problems in identi- fying his state of food repletion and depletion (Hebben et al., 1985). He also ate a second meal within 1 min of finishing the first. Rozin et al. (1998) found that 2 amnesic patients with hippocampal damage similar to that of H.M. consumed two lunches in quick succession, and usually began to consume a third meal if it was offered. Furthermore, reminding neurologically intact participants of the lunch that they ate earlier on the day of a study inhibits their subsequent consumption of snacks, relative to consumption in a condition in which participants are re- minded of the lunch they ate the previous day (Higgs, 2002).

Despite these intriguing findings, little is known about the mechanisms underlying multiple-meal eating in amnesia. Because the procedure in previous studies has been to offer the same meals in succession, one explanation is that the usual decline in palatability and intake of a food that has been eaten to satiety is disrupted in amnesia (Rolls, Rolls, Rowe, & Sweeney, 1973). In the first experiment reported here, we tested whether 2 densely amnesic patients with bilateral damage to the medial temporal lobes reported such sensory-specific satiety. This experiment also provided an opportunity to test whether explicit memory of having recently eaten a food is required for the expression of sensory-specific satiety (Rozin et al., 1998). In our second experiment, we checked whether our patients ate multiple meals as they were offered. Finally, to control for the possibility that the amnesic patients had deficits in taste per- ception or were biased in their use of our rating scales, in our third experiment we assessed their hedonic ratings of yogurt samples differing in sweetness.

METHOD

Test of Sensory-Specific Satiety in Amnesia

Participants Two amnesic patients (S.P. and G.A.) and 8 control subjects (4 men and 4 women; age range = 53-58) participated in this experiment. Both patients had lesions that included medial temporal and frontal lobe structures (see Fig. 1). G.A. was for- merly a professional musician, and S.P. had been a bank man- ager. Both had a category-specific recognition deficit for living things following infection from herpes simplex encephalitis (Humphreys & Riddoch, 2003), and both were anosmic. Each patient completed neuropsychological testing, which confirmed a selective impairment in long-term memory for new material disproportionate to deficits in general cognitive or intellectual functioning (see Table 1). All procedures were approved by the

Address correspondence to Suzanne Higgs, University of Birming- ham, Edgbaston, Birmingham, B15 2TT, England, e-mail: s. higgs. 1@ bham.ac.uk.

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Sensory-Specific Satiety in Amnesics

Fig. 1. Common areas of brain damage for the 2 patients. The right hemisphere is on the right. Common areas of damage include anterior and middle cingulate (bilateral), superior medial frontal cortex (left), middle orbitofrontal cortex (right), rolandic operculum (bilateral), putamen (right), amygdala (bilateral), insula (bilateral), parahippocampal region and hippocampus (bilateral), superior temporal cortex (bilateral), temporal pole (right), and fusiform gyrus (right). From left to right, the slices run from lowest to highest; the position of the slices is shown on the right.

Ethics Committee of the School of Psychology, University of Birmingham, and the participants gave informed written consent.

Procedure

Sensory-specific satiety was measured by comparing the change in liking and desired intake of a food that was eaten to satiety with the change in liking and desired intake of foods that were only sampled. Participants rated four samples before and after consuming one of the foods (sandwiches) as lunch. As in previous studies, ratings of the sampled foods were averaged for comparison with the food eaten to satiety.

Testing took place individually between 12:00 and 2:00 p.m. On arrival, participants rated their feelings of "hunger," "fullness," and "thirst" using 100-mm line scales (anchors were not at all, on the left, and very, on the right). They then tasted the four samples and rated their liking for and desired intake of each, using similar scales. The questions were "How much do you like the taste of this food?" "How much do you like the texture of this food?" and "How much of this food could you eat?" For the first two questions, the anchors on the rating scales were not at all, on the left, and extremely, on the right; for the third question, the anchors were nothing at all, on the left, and a large amount, on the right. The foods, which were selected for their different sensory properties, were (a) a quarter of a chocolate-chip cookie (Cookie Coach Co., Manchester, England), (b) 2 tablespoons of rice pudding (Muller rice; Muller Dairy, Shrewsbury, England), (c) two potato chips (Walkers Crisps, Leicester, England), and (d) one eighth of a sandwich made from two standard slices of bread (ham or chicken; Ginsters, Cornwall, England). The samples were served individually as small portions, in a random order. A glass of tap water was provided for participants to sip in between making their ratings. A separate piece of paper was used for rating each food, and participants were instructed to eat all of each sample.

After removal of the sample foods, participants consumed sandwiches to satiety. Two sandwiches (four slices of bread) were cut into quarters to provide eight portions (approximately 40 g and 96 Kcal per portion). Once the participants had helped themselves to as many portions as they wanted, the sandwiches were removed. Five minutes later, a second set of sample foods was presented, and participants once again rated their liking for and desire to eat each sample, as well as their hunger and fullness and thirst. The sample foods were then removed. Five

minutes later, the patients were asked if they had just eaten. They were informed that they had in fact just eaten and were asked to select the food (from a list of the four foods sampled) that they had eaten in a larger quantity than the others. The patients were tested in three (S.P.) or seven (G. A.) sessions separated by at least a week. Each session was identical. S.P. attended fewer sessions because he had to travel some distance to be tested. The control subjects were tested on one occasion each.

A follow-up session with G.A. tested the generalizability of the results to different foods. The procedure was the same as that just described, but the foods were sandwiches, apple slices, biscuits, and cheese pastries. The cheese pastries were consumed to satiety as lunch.

Multiple-Meal Study In a separate study, participants were served two lunches, separated by 15 min. Each lunch consisted of eight portions of tuna or ham sandwiches (Ginsters, Cornwall, England; approximately 40 g and 96 Kcal per portion) and four portions of cake (Lemon Cake, The Handmade Flapjack Co., Coventry, England; approximately 35 g and 148 Kcal per portion). Participants helped themselves to as much food as they wanted. When they had finished eating, evidence that a meal had been consumed was removed. Fifteen minutes later, an identical meal was presented, and the participants were asked to help themselves to as much as they wanted. Before and after lunch, participants completed line rating scales assessing their hunger and fullness. G.A. and S.P. were tested twice each, and 4 age-matched, male control subjects were tested once.

Hedonic-Ratings Study Using the 100-mm line scales described previously, participants in the third experiment (G.A., S.P, and 2 age-matched, male control subjects) rated their liking for the taste of five samples of yogurt differing in sweetness. Sucrose (Tate and Lyle, United Kingdom) was added to plain full-fat yogurt (Coberco, Arhem, The Netherlands) at the following concentrations: 1, 5.9, 10, 17.6, and 30% sucrose/yogurt by weight. The 10% concentration was equivalent to the sugar concentration of commercially available flavored yogurts. Fifty-milliliter portions of yogurt were served in opaque plastic cups and presented in a random order. Participants consumed enough to be able to make the ratings

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S. Higgs et al.

TABLE 1 Results of Neuropsychological Testing of the Patients

Control Measure G.A. S.R data

Visual short-term memory Corsi block test 5 7 5(2)

Verbal short-term memory Digits forwards 7 7 7(2) Digits backwards 4 6 5(2) Sentence Repetition (PALPA Test 55; W = 60) 57 60 60(0)

Word Repetition (varying number of syllables, PALPA Test 30; W = 24) 24 24 24(0)

Long-term memory WRM Words (N = 50) 24 31 45.3(3.4) WRM Faces (N = 50) 31 33 44.3(3.5) WMS Logical Memory 2 5 22.5(6.3) WMS Visual Reproduction 6 5 29.0(5.2)

Executive function Brixton test (N = 54) 41 42 50a Stroop test (N = 112) 11 92 112(0) WCST 48(3) 98(6) 67.5(5.5) N ART IQ equivalent 103 110 100a

Comprehension (Synonym Matching, PALPA Test 50) High imageability (N = 60) 60 60 60(0) Low imageability (N = 60) 58 57 60(0)

Smell UPSIT 10.0 14.0 30.8

Note. N = number of items. G.A. is a 49-year-old male whose amnesia results from herpes simplex encephalitis, contracted 14 years prior to this study; his clinical symptoms are amnesia, category-specific recognition deficit, and dysexecutive symptoms. S.P. is a 51-year-old male whose amnesia results from herpes simplex encephalitis, contracted 6 years prior to this study; his clinical symptoms are amnesia, category-specific recognition deficit, and mild dysexecutive symptoms. Scores in boldface indicate significant impairment relative to normal. Control data are provided in the norms for the Corsi block test (Kessels, van Zandvoort, Postma, Kappelle, & de Haan, 2000), the War- rington recognition memory (WRM; Warrington, 1984) test for words and faces, the Wechsler Memory Scale (WMS; Wechsler, 1999), the Brixton test (a test of visual problem solving and executive function; Burgess & Shallice, 1997), the clinical Stroop test (Trenerry, Crosson, DeBoe, & Leber, 1989), the Psycho- linguistic Assessment of Language Processing in Aphasia (PALPA; Kay, Lesser, & Coltheart, 1992), and the Wisconsin Card Sort Test (WCST; Heaton, Che- lune, Talley, Kay, & Curtiss, 1993). Control data for the University of Penn- sylvania Smell Identification Test (UPSIT; Doty, Shaman, & Dann, 1984) come from 4 male control subjects age-matched to the patients. In all other cases, control data come from 30 control subjects age-matched to the patients. For the control data, standard deviations are given in parentheses. NART = National Adult Reading Test (IQ equivalent; Nelson & Willison, 1991). aThe control data for the Brixton test and NART IQ equivalent are average normal scores.

(one or two spoonfuls) and rinsed their mouths with water in between samples.

Analysis In the first experiment, the amnesic patients' sensory-specific- satiety ratings (change in rated liking and desired intake) were averaged over three (S.P.) or seven (G.A.) sessions, and then

these averages and the control subjects' ratings were analyzed by a two-way analysis of variance with rating type (pleasantness of taste, pleasantness of texture, desire to eat) and food type (food eaten to satiety, sampled food) as within-subjects factors and group (patient, control) as a between-subjects factor. Intake of the sandwiches as lunch and change in rated appetite and thirst were averaged for the patients across sessions and com- pared with the control data using a two-tailed t test. Intake in the multiple-meal study was analyzed by t test.

RESULTS

Test of Sensory-Specific Satiety in Amnesia The patients could not remember having eaten when questioned after the second set of ratings, and on average correctly identi- fied the food eaten in a larger quantity 38% of the time. Nev- ertheless, the main effect of food type was significant, F(l, 16) =

6.6, p < .05; both the patients and the control subjects showed a decline in rated liking for and desire to eat the food eaten to satiety relative to the sampled foods. There was no effect of group, F(l, 16) = 0.038, p = .5, or of rating type, F(2, 32) = 0.7, p = .5, nor were there any significant interactions (all ps > .3). Figure 2 shows that the rated liking for and desire to eat the sandwiches decreased after they had been consumed as lunch, but that the rated liking for and desire to eat the other foods (cookies, potato chips, and rice pudding) did not change.

Changes in rated hunger and fullness (difference between ratings before and after lunch) differed between patients and control subjects, t(S) = -3.0, p < .05, and t(S) = 2.3,/? < .05, respectively. The control subjects showed the expected changes (mean change = -29.9 mm for hunger and 37.1 mm for fullness), but the patients' rated hunger and fullness did not change (mean change =1.1 mm for hunger and -4.5 mm for fullness). There were no significant differences for rated thirst. The patients also tended to eat more of the lunch than did the control subjects (patients: M = 362 Kcal, SD = 39; control subjects: M = 224 Kcal, SD = 106), t(S) = -1.70, p = .1.

In the follow-up session with G.A., his rated liking of the cheese pastry decreased after he had eaten it to satiety (change in rated liking = - 5 mm for taste and -46 mm for texture), but his liking for the taste of foods that he had only sampled (sandwiches, apple slices, and biscuits) increased (change in rated liking = 15 mm for taste. (Liking for the texture of foods he had only sampled did not change; change in rated liking = -3 mm for texture). When rating the pastry for the second time, G.A. said it tasted "sour." Furthermore, he chose one of the uneaten foods (sandwiches) when asked what he would most like to eat, and could not remember eating the pastry.

Multiple-Meal Study On average, the patients consumed nearly 2,000 Kcal over the two lunches, which was significantly more than the con-

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Fig. 2. Mean changes in patients7 and control subjects' rated liking for taste and texture and rated desired intake of food in the sensory-specific- satiety study. Results are shown for the food eaten to satiety (sandwiches) and foods that were only sampled. Mean change in rating was calculated

by subtracting the rating before consumption of the lunch from the rating after consumption of the lunch. Negative ratings indicate a decline in

liking or desire to eat after lunch. Error bars indicate standard errors of the means.

trol subjects consumed, £(4) = -4.1,/? < .05 (Fig. 3). Only 1 of the 4 control subjects ate something at the second lunch, whereas both patients ate almost as much at the second lunch as they did at the first. Among the control subjects, premeal rated hunger decreased between the first and second lunch, and premeal rated fullness increased (change in hunger =

Fig. 3. Patients' and control subjects' mean intake at two consecutive lunches in the multiple-meal study. Control subjects (n = 4) were tested once, and G.A. and S.P. were tested twice each. The black portions of the bars refer to the first lunch, and the white portions refer to the second lunch.

-35 mm, change in fullness = 26 mm). In contrast, the patients' ratings of their appetite did not change between the first and second lunch (change in hunger = 7.3, change in rated fullness = 7.8).

Hedonic-Ratings Study The patients' ratings of the pleasantness of the yogurt increased monotonically with increasing sucrose concentration and did not decline even for the sweetest yogurt. In contrast, the rating function for the control subjects had an inverted-U shape; their liking of the yogurts increased as the amount of sucrose in-

TABLE 2 Results of the Hedonic-Ratings Study

Yogurt sample G.A. S.P. Control data

1% sucrose 4 12 17 5.9% sucrose 13 43 67 10% sucrose 59 44 74 17.6% sucrose 68 73 44 30% sucrose 65 65 22

Note. Ratings were made on a 100-mm line scale, anchored by not at all pleasant, on the left, and extremely pleasant, on the right. The control data are from 2 age-matched control subjects.




S. Higgs et al.

creased, up to an inflection point of 10%, after which liking declined (see Table 2).

DISCUSSION

The data show that reported multiple-meal eating by amnesics is unlikely to be due to a failure of sensory-specific satiety. Both the patients and the control subjects in our first study showed a decline in rated liking of a food consumed to satiety, whereas only the patients showed hyperphagia. We further conclude that it is not necessary to remember having eaten a food in order to express sensory-specific satiety to that food, because neither of the patients was aware of having just eaten when queried after lunch. This finding suggests that cognitive processes based on explicit expectations about normal portion size, or on memories of having eaten, do not underlie sensory-specific satiety. A likely mechanism may be habituation of responses to the sensory properties of an eaten food (Swithers & Hall, 1994). Our data also suggest that the decline in pleasantness of an eaten food is not sufficient for someone to terminate a meal, because in the second study, the patients, who had previously shown sensory- specific satiety, ate a second lunch 15 min after consuming an identical first lunch.

Brain areas other than those damaged in S.P. and G.A. are likely to be important for the expression of sensory-specific satiety. This hypothesis is consistent with reports that the neural correlates of sensory-specific satiety are found in orbitofrontal cortex (Critchley & Rolls, 1996), rather than medial temporal structures. Processing of the pleasantness of taste stimuli is represented in anterior regions of the orbitofrontal cortex (Kringelbach, O'Doherty, Rolls, & Andrews, 2003), which is consistent with the findings that orbitofrontal damage in S.P. and G.A. is restricted to the right hemisphere and that anterior sections in both hemispheres are spared.

The possibility that the hyperphagia observed is unrelated to the memory deficits of the patients should be considered. Amygdala damage, common to both of these patients, has been associated with hyperoral behavior (in Kliiver-Bucy syndrome). However, we saw no evidence of behaviors associated with Kliiver-Bucy syndrome in these patients. Both patients also had some bilateral damage to the insula, and such damage is known to cause gustatory and olfactory deficits (Pritchard, Macaluso, & Eslinger, 1999; Small et al., 2003). Our findings are consistent with the patients having some gustatory and olfactory deficits: Although G.A. and S.P. could discriminate among sweetened yogurts, unlike the control subjects they did not show reduced liking for the very sweet yogurt. They are also both anosmic. However, it is unlikely that these gustatory and olfactory deficits can explain their hyperphagia, because lesions of the insula are not associated with overeating (Mathy, Dupuis, Pigeolet, & Jacquerye, 2003). Furthermore, although increased preference for sweetness is seen in normal aging (Murphy & Withee, 1986), aging is generally associated with reduced

food intake. Finally, the patients ate more of both foods, not just the sweet food, in the multiple-meal study. Another possibility is that the patients' overeating reflects perseveration re- sulting from damage to the frontal cortex; however, the patients showed no evidence of persistent responses in using the rating scales.

Alternatively, the most powerful cue for terminating a meal may be the social norm that eating should stop after a meal has been consumed (Rozin et al., 1998), and amnesic patients may eat beyond the bounds of what is considered "normal consumption" because they cannot remember having just eaten (because of damage to the hippocampus). However, the patients differed from the control subjects in that their rated appetite did not change in line with changes in their nutritional state, and this suggests that their hyperphagia may be related to processing of visceral satiety signals. Supporting this possibility, data from rats with selective lesions to the hippocampus suggest that the hippocampus is required for internal-state signals to organize eating behavior (Clifton, Vickers, & Somerville, 1998; David- son, 1993). Similarly, amnesic patients may be unable to use bodily sensations arising from the ingestion of food. Meal- induced changes in appetite (which were impaired in the patients) may be cognitively mediated and depend on the con- junction of memories of internal-state cues, food-related sensory cues, and information about the previous postingestive conse- quences of consuming a food (Baker, Booth, Duggan, & Gibson, 1987; Booth, 1977). Failed configuration learning, due to hippocampal damage, could thus contribute to overeating (Suth- erland & Rudy, 1989). Finally, explicit memory that food has been eaten may be required to label internal cues associated with food ingestion. A study supporting this possibility has shown that the behavioral effects of drug-induced bodily states depend on cognitive variables that affect the labeling of those states (Schachter & Singer, 1962).

In conclusion, our data demonstrate that impaired sensory- specific satiety cannot account for the phenomenon of multiple- meal eating in amnesia. The patients in this study showed sensory-specific satiety although they had no explicit memory for having eaten food and ate multiple meals.

Acknowledgments - This work was supported by grants to the first and last authors from the Biotechnology and Biological Research Council and the Medical Research Council, United

Kingdom, and by a fellowship to the third author given jointly by the Economic and Social Research Council and the Medical Research Council, United Kingdom. We thank G.A. and S.P. for their kind participation in the studies.

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