activity based on anatomical structure, oo | 4 x08 ye se _ 12 ne oe® tion ger ' omo 1, 2, 3 act re gee go 1 o? ace 2 “08 wr? 01 1 1 T 1 Fig. 3. Difference between groups of neurons in different brain areas significant at P equalto or less than .05 by the MannWhitney test. Entries are as follows: (1) changes from quiet to paradoxical sleep were different between the two areas, (2) changes from quiet sleep to quiet awake were different between the two areas, (3) changes from quiet sleep to the motivated awake state were different between the two areas. recordings were regularly taken from the layer of hippocampal pyramidal cells in the dorsal anterior part. Neurons here were identified by their large ratio of signal to background (Fig. 2, right-hand column). The increments over quiet sleep rates observed in the quiet awake state were not only smaller than those observed in + paradoxical sleep, but were also less differentiated by anatomical structure. Units in the lateral hypothalamus again had the largest increments in rates, with an average increase of more than 200 percent, itself significant by statistical tests. Also, the hypothalamic group of neurons differed with respect to the size of the increase from those in reticular formation, parietal cortex, preoptic area, and hippocampus. The other brain areas had average rate increments of 50 percent or less. There were no average decrements and no other significant differences between areas, There was an almost total absence of differentiation according to anatomical structure when differences between quiet sleep and motivated awake be- havior were considered. From the 21 paired comparisons of the seven groups, taken two at a time, only one yielded a statistical significance; this was between the lateral hypothalamus which had the largest increments and the dorsal hippocampus which was unchanged. Clearly, paradoxical sleep empha- sized regional groupings of neuronal 8 DECEMBER 1967 behavior empha- process, this would suggest a reduced information content in paradoxical sleep. It might nevertheless be involved in the clearing of temporary information registers on the one hand * ge pod? 1,2] motivated sized individual differences between units. If one might assume that a differentiated pattern of excitation and inhibition would occur within a structure under the influence of an informa- . ag\o or in discharging unspent motive force on the other. The clear lead of hypothalamic process might favor a motivational interpretation because of the known “drive and reward” centers housed there. On the other hand, the reduction in hippocampal discharges might contribute to the clearing of any reverberatory processes involved in temporary information stores often suspected to occupy that region. One appealing supposition combines the two views. It is that the organism generates drive processes on the basis of physiological needs, but that there is an excess of drive which provides a cushion or safety factor. Paradoxical sleep would occur after it was established that the needs werefilled, and it would Successiveness Discrimination as 2 Two-State, Quantal Process Abstract. The duration of the “psy- chophysical time quantum’ measured through the application of a two-state model of successiveness discrimination is equal in magnitude to the modal zero-crossing interval of the alpha rhythm, The two quantities have similar distributions and they are correlated over individuals. The most recent review of the concept of a psychological unit of duration is the monograph by White (7). He considers many lines of evidence which indicate the existence of such a unit somewhere within the range from 50 to 100 msec and heraises again the speculation that the unit may be related to some rhythmic brain process. The alpha rhythm of the electroencephalogram has a period of approximately 100 msec and it is often suggested as a correlate. Later experi- ments by others (2) support this connection by showing associations between certain temporal characteristics of alpha rhythm and of behavior. I have also presented some reasons for thinking of psychophysical time in function to dissipate the excess drive. WALTER D. MINK ' quantal terms (3). In that paper, the time quantum is identified with three Department of Psychology, Macalester College, St. Paul, Minnesota 55101 different behavioral parameters, and . E. Evarts, private communication. . P. R, Huttenlocher, J. Neurophysiol. 24, 451 (1961); E, V. Evarts, Fed. Proc. 19, 828 (1960); J. Neurophysiol. 25, 812 (19623; ibid. 27, 152 (1964); E. M. Podvoll and S, J. Goodman, Science 155, 223 (1967), 7.3. Olds, Excerpta Med, Int. Congr. Ser, 87, 372 (1965). 8. J. E. Swisher, Science 138, 1110 (1962); E. Roldan, T, Weiss, E. Fifkova, Electroencephalog. Clin. Neurophysiol. 15, 775-785 (1963). 9. Research supported by PHS research grants to the Brain Research Laboratory of the University of Michigan. We thank Giulio Baldfighi for technical assistance in the surgical preparation of animals, and Fred Coury and William Wetzel for assistance in the design and construction of apparatus, W.D.M. was a NSF science faculty fellow, and P.J.B. was a NSF postdoctoral fellow during part of the time of the research. measurements show that the magnitude of the quantum is very close to 50 msec in all three cases. This is approximately the same as the interval between zerocrossings of the alpha rhythm, and additional measurements are given which indicate a positive correlation over individuals between this alpha interval and the behavioral quantum. However, the number of experimental subjects was small, and the average values of the behavioral parameters exceeded the average alpha interval by 6 or 7 msec in all three cases. The present report is concerned with a further analysis of one of the three behavioral parameters and with its relationship to the alpha interval. Additional empirical relationships which support the time quantum hypothesis are also set forth. The parameter under consideration is called M andit is defined in terms of the successiveness discrimination function: the relationship between (i) the probability of discriminating a successive pair of sensory events from a simultaneous pair of sensory events and (ii) the time interval between the members of the suc- 11 October 1967 cessive pair (4). PHILLIP J. BEST JaMEs OLDS Department of Psychology, University of Michigan, Ann Arbor 48104 References and Notes 1. W. Dement and N. Kleitman, Electroencephalog. Clin. Neurophysiol. 9, 673 (1957). 2. W. Dement, ibid, 10, 291 (1958). 3. S. Freud, A General Introduction ta Psychoanalysis (Permabooks, New York, 1958). 4. W. C. Dement, in New Directions in Psychology Hl, T. C. Newcomb, Ed. (Holt, Rinehart and Winston, New York, 1965), pp. 135-257; M. Jouvet, in Sleep Mechanisms, K. Akert, C. Bally, J. P. Schade, Eds, (Elsevier, New York, cA wie? — whereas 1965), pp. 20-57. 1337