Local Infusion of Scopolamine Into Intraparietal Cortex Slows Covert Orienting in Rhesus Monkeys

There is accumulating evidence to suggest that cholinergic neurotransmission may play an important role in visuospatial attention, but the brain sites at which acetylcholine modulates attention are not well understood. The present work tested the hypothesis that the cholinergic influences within the intraparietal cortex are necessary for normal attentional shifting (covert orienting) in nonhuman primates. Two rhesus monkeys were trained to perform a visual, cued target detection task for liquid reinforcement. The animals pressed a lever to produce a visual display in which a central fixation point was flanked by two circles. Shortly after fixation was established, one of the circles brightened (cue), and a target appeared subsequently within one of the circles. Detection was signaled by a manual response and the reaction time to the appearance of the target was recorded. Four types of trials were presented. For valid cue trials, the cue and target were at the same spatial location; for invalid cues, cue and target were in opposite hemifields; for double cues, both cues were brightened but the target appeared in either the left or right circle; in no-cue trials, the cue was omitted. We localized the intraparietal region by recording attention-related, cellular activity with intracerebral microelectrodes. Among visually responsive cells in this area, valid cues presented to the receptive fields of visual neurons enhanced the responses to target stimuli in about half the cells and inhibited those responses in the remainder. In addition, some cells showed longer response latencies to invalid cues than to valid cues. We then infused scopolamine into attention-related activity sites and assessed its effect on performance. Scopolamine produced a dose-dependent increase in reaction times and decrease in performance accuracy that lasted more than 1 h. Neither vehicle injections in the same locations nor scopolamine outside the physiologically defined area produced any significant change in behavior. Under our conditions of measurement, we conclude that activity mediated by muscarinic cholinergic receptors within the intraparietal cortex is necessary for normal covert orienting.

Performance of Malnourished Rats on the Hebb-Williams Closed-Field Maze Learning Task

3 groups of rats were subjected to protein restrictions during development, while two control groups received normal diets throughout the experiment. The protein restricted groups were raised on dams that were maintained on 12% protein diets and were weaned at 21 days of age to a diet containing 3% protein. One group was maintained on the diet for 7 wk. and then rehabilitated on a 21% protein diet while a second group was maintained on the 3% protein diet for 27 wk. and then rehabilitated for 7 wk. At this time these two groups and a control group maintained on a normal dam prior to weaning and maintained on 21% protein throughout the experiment were tested on a Hebb-Williams maze for liquid reinforcement. The third diet-restricted group was maintained on the 3% protein diet throughout the experiment and was tested in the Hebb-Williams maze along with a control group raised on 21% diet when they were 6 mo. of age. The nonrehabilitated group made the most errors and differed significantly from both the control groups and the rehabilitated groups. The rehabilitated groups did not differ significantly from one another, but they made significantly more errors than the nonrehabilitated groups. The effects of early diet restriction were compared with the effects of early environmental restrictions in their effects on problem-solving behavior.