A comparison of the effects of inferotemporal and striate cortex lesions on the visual behaviour of rhesus monkeys

The effects of bilateral removal of inferotemporal cortex or lateral striate cortex are compared. The former operation impairs visual pattern discrimination learning, without disturbing prompt detection and retrieval of food, visual acuity or visual fields. In contrast, animals in which the macular striate projection area has been removed are significantly superior in tests of visual pattern discrimination learning despite showing impairment of visually guided reaching, visual acuity, and visual fields. The results indicate that the inferotemporal defect is not caused by deficient visual sensitivity or acuity.     

Effects of prestriate, inferotemporal, and superior temporal sulcus lesions on attention and gaze shifts in rhesus monkeys.

The role of extrastriate cortical areas in selective attention was studied in 12 rhesus monkeys. Animals learned a series of color-form pattern discrimination problems, with either color or form cues relevant. After each problem was mastered, correct behavior required a shift in attention, i.e., that responses be made to be previously irrelevant dimension. On some problems shifting attention required that the animal maintain the same fixation; on other problems the color and form cues were separated in space, and the attention shift presumably required a shift in gaze. Matched groups of animals with inferotemporal, prestriate, or superior temporal sulcus lesions, and normal controls, differed significantly in their ability to shift attention. Analyses of inferred stages in attention shift showed that different processes were disturbed in the three lesion groups. Results are discussed in terms of cortical substrates for "looking" and "seeing".     

Drug discrimination using a conditioned taste-aversion paradigm in rhesus monkeys.

The development of drug discrimination was assessed in rhesus monkeys using the conditioned taste-aversion paradigm. Monkeys were initially trained to respond under a fixed-ratio 30-response schedule of food-pellet delivery to assess the rate-decreasing effects of alprazolam (0.03 to 3 mg/kg, i.m., 60 min presession). Alprazolam decreased responding at doses greater than 0.1 mg/kg. Discriminative stimulus effects of alprazolam were then assessed by giving 0.03 mg/kg before sessions in which 1.8 mEq/kg lithium chloride was given immediately after the session (alprazolam/lithium session). On intervening days, saline was given before and after the session (saline/saline session). Rates of responding decreased over successive alprazolam/lithium sessions and also during the saline/saline session that immediately followed an alprazolam/lithium session. During subsequent saline/saline sessions, rates of responding returned to levels near baseline rates within two to four sessions. The discriminative stimulus effects of alprazolam were then assessed by giving 0.1 mg/kg before sessions in which 1 mg/kg d-amphetamine was given immediately after the session (alprazolam/d-amphetamine session). Rates of responding decreased during subsequent alprazolam/d-amphetamine sessions in drug-experienced monkeys, but did not decrease during intervening saline/saline sessions. These findings demonstrate that drug stimuli associated with postsession drug injections can rapidly develop control over behavior and suggest that similar methods be explored in the assessment of drug discrimination.     

Operant discrimination of an interoceptive stimulus in rhesus monkeys

Five rhesus macaques monkeys surgically prepared with Thiry small intestinal (jejunum) loops and implanted brain electrodes were restrained in primate chairs and kept on 23-hr deprivation-feeding cycle. After being trained to press a lever for sugar pills on an FR 25 schedule of reinforcement, a discrimination training procedure was established. Lever presses were reinforced during the S(D)-a non-aversive mechanical stimulus applied to the internal walls of the Thiry loop by rhythmic inflation-deflation of a small latex balloon by air at the rate of one cycle per sec at 100 mm Hg pressure. The S(Delta) was the absence of the visceral stimulation. The monkeys successfully discriminated between presence and absence of the internal stimulus. A discrimination reversal was attempted and completed on one monkey. The results clearly show operant discrimination based on an interoceptive stimulus. Cortical and subcortical EEG records reflected the onset but not termination of the visceral stimulation.     

Visual discrimination learning in rats with lesions of superior colliculus: Door-push and approach errors in modified jumping stand

It has been suggested that, for some species, lesions of the superior colliculus affect visual discrimination learning, but only in certain conditions: (a) when problems are first learnt only after operation, or (b) when discriminanda require detailed scanning, or (c) when “approach” responses to the discriminanda are measured, rather than the response of actually touching them. These suggestions were examined in rats learning visual discriminations in a modified jumping-stand apparatus, after sustaining large lesions of the superior colliculus (and in some cases also of the pretectum). The lesions produced open-field hyperactivity and reduced exploration, indicating effective tectal damage, but the rats learnt a series of difficult discriminations in a door-push task as fast as normal rats, and they did not make more approach errors. Their main abnormality in the discrimination apparatus was that they looked less often between the stimulus doors before stepping across to one of them from the central platform. It is suggested that in rats, as in other animals, lesions of the superior colliculus disrupt the control of scanning head and eye movements; in rats, however, such disruption need not affect discrimination learning (at least in some kinds of apparatus), possibly because the retina of the rat has a relatively poorly developed area centralis.     

Factors influencing sexual performance in male rhesus monkeys.

A 5-yr retrospective study of the sexual behavior of eight adult male rhesus monkeys showed that sexual vigor declined over the years but testosterone levels in peripheral vein plasma did not. Two prospective experiments were then carried out on these males during the sixth year. (a) The four poorest performers were injected daily for 28 days with testosterone propionate (1 mg/kg of body weight). There was no significant increase in level of performance, and behavior was not correlated with plasma levels of testosterone either before or 24 hr after the last hormone injection. (b) All eight males were exposed to novel nonspecific sensory stimulation during tests of sexual behavior. Eight different adult male rhesus strangers-present in the room but not in the test cage-were used as stimuli, one for each experimental test. Sexual behavior during experimental and control tests did not differ.