Sey
ihe
aT
a ete eae ds pate tei
are et ee
25. D. S. Ray and P. C. Hanawalt, J. Mol. Biol.
11, 760 (1965); M. Edelman, J. A. Schiff, H.
T. Epstein, ibid., p. 769; M. Edelman, H. T.
Epstein, J. A. Schiff, ibid. 17, 463 (1966).
%. E. G. Pringsheim and O. Pringsheim, New
Phytol. 51, 65 (1952),
27. After completion of this manuscript, R. B.
Webb and M. M. Malina [Science 156, 1104
(1967)] reported a mutagenic effect of visible
light (> 408 nm) in E. coli in the absence of
an exogenous photosensitizing pigment.
28, D. I. Amon, Plant Physiol, 24, 1 (1949),
29. Supported in part by PHS research grant
GM-07984.
26 July 1967
Neurons in Paradoxical Sleep
taken with electrodes permanently implanted in unrestrained rats during
normal sleep, paradoxical sleep, quiet
awake, and highly motivated awake
periods. In most areas, neuronal activity
increased when normal sleep changed
to paradoxical sleep. The hypothalamus
showed a significantly greater increase
than most other areas. The hippocampus differed strikingly from all
other areas by showing a decrement in
all cases. The average firing rates in
paradoxical sleep exceeded those of the
quiet awake state as well as those of
normal sleep. Comparison of paradoxi-
cal sleep with motivated behavior illustrated that changes in brain activity
during paradoxical sleep were related to
anatomically specifiable groupings, but
no such differentiation appeared in motivated behavior.
The state of paradoxical sleep in
animals has been a matter of keen interest because of its relation to the state
of dreaming in man. The work of
Dement and Kieitman (/) established
that a paradoxical arousal of electroencephalographic activity occurred periodically during sleep in man and thatit
was correlated with the state of dream(2)
showed
prior to the placing of stronger bonds
in a long-term store (5). From a less
theoretical point of view, there are
significant questions related to the
similarities and differences between
dream-sleep and waking; if the brain is
active during dream sleep as it is in
Abstract. Single-cell recordings were
Later Dement
being involved in the dissipation of
weak bits of associational mformation
waking, why is there no behavioral out-
and Motivated Behavior
ing.
peutic mechanism. The notion of information processing also figures
prominently in a nonmotivational interpretation, namely that dreams function
in the laying down of memory stores,
the
similarity of paradoxical sleep in animals and man. The question of the
function of the two states of sleep does
put, and why does experience in this
period lack the coherent organization of
that of the waking brain?
Contributions toward the understanding of the questions involved have derived from physiological research on
paradoxical sleep in man ami animals.
During paradoxical sleep, as in waking,
low-voltage, fast activity appears in the
electroencephalograms (EEG) taken
from most forebrain and midbrain
points, and a higher more rhythmic and
slower “theta” pattern with higher volt-
age is recorded from the hippocampus
and related areas. There is also a powerful downstream inhibitory process act-
ing toward the spinal cord; this process
expressed in a depressed muscle tone
which is even lower in this state than
it is in normal sleep and is quite unlike
anything observed in the awake animal,
These patterns taken together are the
defining characteristics of paradoxical
sleep (4).
There is a very large imcrease in
neuronal activity in the midbrain and
forebrain (6). There is often a greater
discharge frequency during paradoxical sleep than during either quiet sleep
or quiet awake periods. It is most
marked in the reticular formation and
thalamus but is also apparent to a lesser
degree in caudate, putamen, hippocam-
pus, amygdala, cochlear mucleus, and
colliculi.
While the large downstream inhibitory process may account for the
not have a clear answer. Freud (3)
lack of output from a generally ac-
fantasied wish fulfillment, satisfying
strong motivational urges and permitting sleep to continue. Motivational interpretations have received some sup-
of the dream state and awake states.
We have compared neuronal activity
thought dreams constituted a kind of
port from work on deprivation of para-
doxical
sleep
in
animals
(4); these
Studies might be considered to suggest
that dreams constitute the discharge of
the
brain’s
unspent
motivational en-
ergies as a sort of built-in psychothera8 DECEMBER 1967
tivated brain there are still unanswered questions about the relation
during paradoxical sleep not only with
that of sleep and quiet awake states but
also with that of a highly motivated
period in order to answer the following
questions, First, can any detailed differ-
ences be specified between the dream
state and the quiet and motivated awake
states? Second, does the whole brain
participate in the activity increments
during paradoxical sleep, or do the
slow, theta rhythms which characterize
hippocampal recordings and those from
some other areas during this period indicate an actual depression of activity
in some areas? Third, is there a clear
and significant predominance of some
areas over others during this period of
general activation which might help to
clarify the relation between informational and motivational interpretations
of the process?
In these studies, we implanted six to
eight fixed wire microelectrodes in male
albino rats. The electrodes were stereotaxically aimed and guided by singleunit recording. Animals were trained to
remain motionless for aperiod of 2 seconds while depressing a pedal to obtain
food or water. Recording sessions oc-
curred during a period of 3 to 4 weeks.
Units were identified on the basis of
amplitude and wave form. Movement
was detected by a hearing-aid wire
which was wrapped loosely around the
cable that carried the microelectrode
signals; movement of the cable generated voltages in it. A more complete
description of the unit-discrimination
procedure has been reported (7).
During sleep and quiet wakefulness,
samples were taken at a rate of about
one sample every 3 seconds, but they
were accepted for computations only
if no movement occurred during the
2-second sample period. Records were
also obtained during successful 2-second movement-free pedal presses for
food. The digital output of five unitdiscriminators was recorded on EEG
paper during sample periods together
with three channels of EEG, a record
of movement, and indications of the
completion of a successful 2-second
sample and pedal pressing (Fig. 1).
The same information was punched on
papertape.
Records were taken during extended
periods of sleep, ‘usually 2 to 3 hours
long. During this time, the animal was
monitored visually. Records were
obtained during periods of quiet
havior when the animal was awake
during pedal pressing for food.
also
beand
The
EEG records were used to categorize
sleep samples as slow-wave sleep or
paradoxical sleep. Most of the EEG
recordings were monopolar from sub-
cortical locations, and theta activity
(6 to 8 cycle/sec) occurred characteristically during paradoxical sleep.
The cyclical relation of sleep with slow
1335