activity based on anatomical structure,
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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