Elevation and reduction of plasma tryptophan and their effects on aggression and perceptual sensitivity in normal males

Data from experimental animals suggest that 5-hydroxytryptamine (5HT) may have an inhibitory effect on aggression, while clinical studies have found a correlation between pathological aggression and low brain 5HT. To investigate this relationship further we used amino acid mixtures designed to raise or lower the levels of the 5HT precursor, tryptophan. Normal male subjects were given tryptophan-depleted, balanced, or tryptophan-supplemented ammo acid mixtures and tested for aggression 5 hours later. The balanced amino acid mixture served as a control for the tryptophan depletion and supplementation. Testing for aggression was done using the Buss paradigm in which subjects deliver electric shocks to a (nonexistent) partner in response to stimulus tones. Duration and intensity of shock delivered were the measures of aggression, while responsivity to the stimulus tones was the measure of perceptual sensitivity. Neither tryptophan supplementation nor tryptophan depletion had any effect on these measures of aggression or perceptual sensitivity. We conclude that raising or lowering the synthesis of brain 5HT through alterations in tryptophan availability does not influence aggression in normal males as measured by the Buss task.     

Body size as a determinant of aggression during heterosexual encounters in hormone-treated gonadectomized pigs

Aggressive and sexual behavior was studied in 5-minute paired encounters between testosterone-treated castrated boars and estrogen-treated ovariectomized gilts. The boars were either 15 kg heavier (N = 6), or lighter (N = 6), than the gilts (N = 8). Tests were carried out over a 4-week period, during which time each boar was paired once with each gilt; the procedure was replicated over a further 4 weeks. Gilts usually initiated the aggression, especially in the first 4-week period; however, the degree of aggression was positively correlated with body size, irrespective of sex. Aggression was reduced in the second 4-week period in both sexes in tests with large, but not with small, boars. Large boars were more sexually active than small boars, and their sexual performance improved markedly with time, unlike that of the small boars. Champing was positively correlated with aggression duration in pigs of both sexes, and salivation was seen more often in boars than gilts.     

Effects of fluprazine (DU 27716) upon aggressive and sexual behavior of testosterone-treated female rats

Female rats, chronically treated with Testosterone Propionate (TP), were injected with Fluprazine (DU 27716) or saline and tested for social aggression, masculine and feminine sexual behavior. Fluprazine-treated females were less aggressive than saline-treated females, as indicated by a shift from offensive to less offensive parameters of aggression. At the same time, mounting in Fluprazine-treated females was almost totally abolished, both in aggression tests and in tests for sexual behavior. Feminine sexual responses increased during aggressive encounters but were slightly inhibited when females were confronted with sexually active males. Females treated with Fluprazine and tested for mounting with a receptive female showed a substantial increase of offensive aggression directed at the receptive stimulus female. It is concluded that Fluprazine does not selectively inhibit offensive aggression in TP-treated female rats.     

Why and how to use virtual reality to study human social interaction: The challenges of exploring a new research landscape

As virtual reality (VR) technology and systems become more commercially available and accessible, more and more psychologists are starting to integrate VR as part of their methods. This approach offers major advantages in experimental control, reproducibility, and ecological validity, but also has limitations and hidden pitfalls which may distract the novice user. This study aimed to guide the psychologist into the novel world of VR, reviewing available instrumentation and mapping the landscape of possible systems. We use examples of state-of-the-art research to describe challenges which research is now solving, including embodiment, uncanny valley, simulation sickness, presence, ethics, and experimental design. Finally, we propose that the biggest challenge for the field would be to build a fully interactive virtual human who can pass a VR Turing test – and that this could only be achieved if psychologists, VR technologists, and AI researchers work together.     

Impairment in the control of coupled cyclic movements of ipsilateral hand and foot after total callosotomy

Integrity of both cerebral hemispheres is required to control in-phase or anti-phase coupling of ipsilateral hand and foot oscillations, as shown by the impairment of these tasks when performed on the healthy side of hemiplegic patients. On this basis, coupling of hand–foot movements was analysed in a right-handed subject (ME) who underwent a total resection of the corpus callosum. Oscillations of the prone hand and foot, paced by a metronome at different frequencies, as well as EMG activity in extensor carpi radialis (ECR) and tibialis anterior (TA) muscles were analysed by measuring the average phase difference between the hand and foot movements and EMG cycles.

ME performed in-phase movements (right-hand extension coupled to right-foot dorsal flexion) at frequencies up to 3 Hz, though the hand cycle progressively lagged the foot cycle as the frequency increased. At 3 Hz the hand lag reached −142° (as compared to about 25° in healthy subjects). The lag increased even further after application of an inertial load to the hand, reaching 180° at 1.8 Hz (about 50° in healthy subjects). ME's hand lag is caused by the lack of any anticipatory reaction in hand movers. In contrast to healthy subjects, which activate the ECR earlier than the TA when the frequency increases, ME activated the ECR later than TA at all frequencies higher than 0.9 Hz.

Anti-phase movements (hand extension coupled to foot plantar flexion) were performed only upto 1 Hz in unloaded conditions. At 0.6 Hz, movements were in tight phase-opposition (3°), but at 1 Hz, the hand lag reached −34° because of a delayed ECR activation. After hand loading ME was unable to couple movements in anti-phase. In contrast, normal subjects maintain a tight anti-phase coupling up to 2.0 Hz, both with an unloaded or loaded hand. Similar deficits were observed by ME when performing in-phase and anti-phase coupling on the left side, as well as when he was blindfolded.

In normal subjects, an anticipated muscular activation of hand movers compensates for hand loading. Since this compensation must depend on monitoring the hand delay induced by loading, the absence in ME of such compensatory reaction suggests that callosal division had apparently compromised the mechanisms sustaining feedback compensation for differences in the biomechanical limb properties. They also confirm and reinforce the idea that elaboration of the afferent message, aiming at controlling the phase of the movement association, needs the co-operation of both cerebral hemispheres.