Table 1. Median values and ranges for ratios of mean unit activity durmg three behavioral conditions to mean unit activity during sleep with slow waves for 52 electrodes. N, number; Md, median. Location N Paradoxical sleep rats (8). A group of 12 animals was observed, Md Range Md Range providing a total of 52 unit recordings. 11 3.52 0.95- 5.17 2.06 0.83- 4.81 2.84 0.89- 9.28 Electrodes were aimed at the following Lateral preoptic Anterior thalamus 9 7 1.79 1.49 .49- 3.15 .T3- 3.46 1.31 1.48 .92- 1.76 94- 3.40 1.57 2.45 1.11- 2.44 0.75- 3.30 pothalamus, reticular ormation, ventra tegmentum. anterior thalamus, dorsal 0.87- 1.26 0.99 34 1.26 9 2.80 6 194 Parietal cortex 4 Dorsal hippocampus 1.42 6 0.62 Total 52. 1.93 Range BarP food ari Tess,fooe’ Lateral hypothalamus Reticular formation Ventral tegmentum Md k Quiet awake waves to paradoxical sleep in our animals was similar to that reported in .97-20.50 63 2.75 1.51 1.37 .88- 2.09 1.23 34 0.87 1.03 .34-20.50 1.37 .79- 4.25 .55— 3.41 LOI- 1.26 .55- 4.81 1.53 1.13 .95-16.25 .32- 6.20 1.21 .98— 1.53 1.58 .32-16.25 areas: lateral preoptic area, lateral hythal ‘cular f ti tral . n ; hippocampus, and parietal cortex. The number of 2-second samples varied from 350 to 2000. Because rates of response per 2-second period were greatly different from unit to unit, absolute response rates were not used in comparisons but were converted to Anterior Thalamus''} Hypothalamus: 2 Cortex 3 ‘| ratios of a baseline average response rate obtained during sleep with slow waves. The analyses of results were. Reticular Formation 4 I Reticular Formation 5 ! Anterior Thalamus, 6 based on these ratios. The medians and ranges of the ratios were tabulated for each of the stereotaxically defined brain Ventral Tegmentum 7 imacr: Clock - 10 min.) 8 Gate % ' Water Behavior 10 Posterlor Hypothalamus 11 ' | AVA | | 1 SLEEP WITH SLOW WAVES] paRapoxicat’ steep Movement 12 | areas (Table 1). : In total neuronal activity, paradoxical sleep surpassed the quiet awakestate | GuLET AWAKE | s | ; | Food Bahavior 3B Complete Trial - or - Reinforcement 14 Fig. 1. I Sample records of one complete sample interval for the four conditions which were observed. Analog channels are EEG tracings (3, 7, 11) and movement (12); digital channels indicate the readout of unit counters (1, 2, 4, 5, 6) and the state of the behavior sampling system (8, 9, 10, 13, 14). (P<.05), and the latter surpassed quiet sleep (P<.05}. The motivated awake condition was highly variable, falling above the quiet awake state and below paradoxical sleep in mean value but statistically not differing from either. The pattern of changes in rate of firing from normal to paradoxical sleep was highly differentiated by brain locus. The hypothalamus and reticular areas showed the highest increments: both changes were Statistically significant. The median response rate in hypothala- Hypothalamus Hippocampus ad ee ee mus was more than 350 percent of the normal sleep rate, and that in reticular formation was more than 250 percent. The thalamic, preoptic, tegmental, and cortical groups had median increments ranging from 42 to 94 percent; each of the latter three groups was significant- mee a — ly below the hypothalamus in the size of the increments. Histological material showed that the highly augmented cases of hypothalamus occurred in the lateral part, in or near the medial forebrain bundle. The involvement of the medial forebrain bundle was also indicated by the characteristic recordings which usually had a small ratio of signal to Fig. 2. Samples of neuronal activity in lateral hypothalamus and dorsal hippocampus the background, making units difficult to distinguish from one another (Fig. 2, left-hand column). The units of hippocampus showed a consistent decrease in rate of firing during paradoxical sleep. In fact, a decrease was observed in the rate of every hippocampal unit. The hippocampus as an area was significantly different from all the others, the two recording points. decrement (Fig. 3). The hippocampal during normal sleep and paradoxical sleep. Histological sections show the location of 1336 being the only case to show a consistent SCIENCE, VOL. 158