Minoru Shimokochi

The medial preoptic area is involved in both sexual arousal and performance in male rats: re-evaluation of neuron activity in freely moving animals

A total of 74 single unit activities was recorded from the medial preoptic-anterior hypothalamic continuum (MPOA) during free copulatory behavior of male rats. Forty-six units (62.2%) showed changed activities during at least one phase of male copulatory movements; 26 units (35.1%) increased in the firing rate during pelvic thrusting; 32 units (43.2%) increased in activity during backward jumping immediately after intromission; only one unit (1.4%) showed decreased firing rate during thrusting and backward jumping; 12 units (16.2%) increased in activity during pursuit of a female; 19 units (25.7%) were suppressed during genital grooming. Furthermore, 67 units (90.5%) showed a significant change in activity throughout a series of copulatory behavior. From the introduction of a female up to ejaculation, relatively large number of units increased in the firing rate above the value during pre-introduction adaptation period. During postejaculatory interval, however, most units decreased in activity below the level during copulation. These results strongly suggest that the MPOA is involved in both sexual arousal and performance in male rats.

The N400 component of event-related potentials in schizophrenic patients: a preliminary study.

ERPs were recorded during a word recognition task to investigate cognitive dysfunction in schizophrenia. Thirteen medicated schizophrenics and 26 normal controls were tested. In each trial a pair of stimuli, S1 (a word) and S2 (a word or a non-word), were presented. The subjects were required to discriminate between a word and a non-word for S2 (lexical decision task). In a related (R) condition, S2 was the antonym of S1 (e.g., brother-sister); in an unrelated (U) condition, S1 and S2 were semantically unrelated (e.g., brother-drive); in the non-word (N) condition, S2 was a non-word (e.g., brother-grofe). The ERPs for S2 were analyzed, and the contextual effects on the ERPs for S2 observed for both the patients and controls. For both groups, in the U and N conditions S2 elicited a large negative-trending deflection (N370). In contrast, in the R condition it elicited only a small negative-trending notch. There was no difference in the amplitude of N370 between the groups, but its latency was more prolonged or its wave shape more extended for the schizophrenics than for the controls. The N400 amplitude is concluded to remain unchanged in schizophrenics.

ERPs in schizophrenic patients during word recognition task and reaction times

Event-related brain potentials (ERPs) were recorded in 28 schizophrenic patients and 26 healthy controls during a word recognition task. In each trial, stimuli consisting of S1 (word) and S2 (word or non-word) were presented. The subjects were required to indicate whether S2 was a word or a non-word by pressing buttons. For both groups, a clear N370 was elicited by S2 which were non-word or semantically unrelated to its S1. The N370 amplitude did not differ between the groups. The schizophrenics responded more slowly than the controls, and the latencies of P200 and N370 were longer for patients than for controls. However, these latencies did not differ between the groups when their reaction times were matched.

Studies on the Neural Basis of Behavior by Continuous Frequency Analysis of EEG

Publisher Summary This chapter discusses the studies on the neural basis of behavior by continuous frequency analysis of Electroencephalography (EEG). A number of electroencephalographic studies have been reported that aimed to clarify the neural mechanisms that control conditioned behavior. In some experiments, intracerebral stimulation was used as the conditioned stimulus, as the indifferent tracer stimulus to follow the input, or to influence the conditioned response. The component at 9.5 c/s driven by the reticular stimulation, showed a marked increase in amplitude just before the lever-pressing in the frontal Lead on both sides. The EEG component of the stimulation frequency in the hippocampal lead was replaced by an enhancement of the component at 7–8 c/s because of the hippocampal arousal pattern at that time. The changes of the temporo-occipital and occipito-frontal EEGs correlated with the “switch-off behavior” resembled those of the hippocampal EEG. It is found that when the EEG changes correlated with the switch-off behavior driven by the brain-stem stimulation were compared to those of the spontaneous lever-pressing, a similarity was found in the hippocampus.

Multiple unit activities recorded from the medial preoptic area during copulatory behavior in freely moving male rats

Multiple unit activities (MUAs) were recorded from the medial preoptic area (MPO) during copulatory behavior in freely moving male rats. The baseline firing rate in the male MPO was 19.6 spikes/s +/- 7.1 S.E. (n = 14), and it was increased by 36.7% when a female rat was introduced (26.8 spikes/s +/- 8.9 S.E., n = 14). The firing rate remained elevated until ejaculation. The maximum firing rate (53.5 spikes/s +/- 16.7 S.E., n = 14) was obtained specifically during pursuit-mounting behavior. This high frequency firing with pursuit-mounting behavior was, however, immediately inhibited for 8.2 s +/- 2.1 S.E. (n = 14) when mounting was followed by intromission. The firing-inhibition was further prolonged (120.9 s +/- 44.6 S.E., n = 14) when ejaculation was performed after mounting and intromission. In cases where mounting was elicited alone, a firing-inhibition was not observed and the firing rate after mounting returned to the average firing rate during copulatory behavior. These results suggest that the MPO neurons may play a major role in pursuit-mounting, intromission and ejaculation.

Effects of semantic context and event-related potentials: N400 correlates with inhibition effect

Two experiments investigated the modulation of event-related brain potentials (ERPs) by semantic context. A prime-target pair was visually presented in each trial of a lexical decision task. For word targets, three types of relatedness conditions were employed: (1) Related word condition (e.g., school-teacher); (2) Neutral word condition (e.g., [symbol: see text] - number); (3) Unrelated word c((e.g., hospital-potato). In Experiment 1, the reaction time for unrelated targets was longer than that for neutral targets (inhibition effect) which was longer than that for related targets (facilitation effect). The N400 amplitude in the unrelated targets was larger compared to those in the related and neutral targets, which did not differ. In Experiment 2, where only the facilitation effect was obtained, the N400 amplitude did not differ among conditions.

Modification of male rat copulatory behavior by lateral midbrain stimulation

Effects of electrical stimulation of the lateral midbrain tegmentum (LMT) on the copulatory behavior of male rats were examined in our investigation of the role of the LMT in this behavior. Sexually experienced male rats (n = 15) that had been implanted with chronic electrodes under sodium pentobarbital anesthesia were individually tested for copulation with a receptive female under a 30 s on, 30 s off pattern of stimulation. The ejaculation latency, and mount and intromission frequencies decreased significantly during the stimulation tests, indicative of facilitation of copulation. In contrast, a strong stimulus-bound inhibition of copulation was found in 12 males (80%). Six animals who showed accelerated copulation also depressed the lever for self-stimulation at an identical current during the copulation tests. These results suggest that the LMT functions in ejaculation, in the normal expression of intromission and in sexual reward, thereby regulating the copulatory behavior of male rats.

Involvement of the lateral mesencephalic tegmentum in copulatory behavior of male rats: neuron activity in freely moving animals.

Single unit activity was recorded from the lateral mesencephalic tegmentum (LMT) during free copulatory activity by male rats. Twenty-four (89%) of 27 units showed changes in the firing rate during at least one of the three phases of copulatory behavior: pursuit of the female, pelvic thrusting and genital grooming. The activity of 16 units (59%) increased during pursuit of the female, and the activity of 3 units (11%) increased markedly during pelvic thrusting accompanied by intromission. In contrast, 6 units (22%) were suppressed during thrusting with intromission. Whereas the activity of 10 units (37%) increased during genital grooming, 7 units (26%) were suppressed below the baseline during this behavior. The specific firing patterns of the LMT units that are correlated with the particular copulatory movements are a strong indication that the LMT may have an important function in the execution of male copulatory behavior. Some LMT units may mediate sensory information from the genitals that is needed to display a series of copulatory movements. Other units may be more directly related to reflex-like copulatory movements.

Deviate N200 Component of Event‐Related Potentials in Shuchaku‐Seikaku, a Premorbid Personality of Depression

Abstract: Twenty‐one healthy subjects with Shuchaku‐Seikaku (SS), a premorbid personality of depression, and 44 control subjects were tested for event‐related potentials using the auditory odd ball paradigm. A higher percent of the N200 component was evoked by frequent task‐irrelevant stimuli in the Shuchaku‐Seikaku (81.0%) subjects than in the controls (45.5%). The mean amplitudes in the 50–100 ms latency range for task‐relevant rare stimuli were smaller; whereas, the amplitudes in the 100–200 ms range for task‐irrelevant frequent stimuli and the amplitudes in the 200–260 ms range for both stimuli were larger (shifted to negative direction) in the SS subjects than in the controls. The evidence suggests that the fully automatic detection process, which is assumed to be correlated with mismatch negativity, is hypoactivated and that a contrarily controlled or conscious mismatch process, which may be N2b, is hyperactivated in SS.

Temporal analysis of REM sleep after nest-building behavior in nulliparous albino rat

EEG recording was performed, during nest-building behavior (NBB), from the hippocampus and sensorimotor cortex of nulliparous albino rats with simultaneous recordings of EMGs of neck-muscle and eye movements. The duration of NBB varied with a period of 4-5 days. However, the relative durations of behavioral transitions in NBB, i.e., nest-building, grooming, and sleeping, were regular in both long lasting and early terminated NBB. REM sleep was identified, in every instance, immediately after NBB. The latency of REM sleep was significantly tied to the termination of NBB without regard to the duration of NBB. Differences in the duration of NBB, however, affected REM-propensity: the longer the NBB was, the shorter the latency of REM sleep tended to be. NBB might accelerate the induction of the physiological condition responsible for REM sleep generation.