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