Previous studies have shown that amphetamine can enhance learning in Pavlovian conditioning tasks, but little is known about the changes in neural activity accompanying these performance enhancements. We evaluated the effects of amphetamine (10 mumol/kg) on delay eyeblink conditioning performance and single-neuron activity in the anterior cingulate cortex (area 24) of the rabbit (Oryctolagus cuniculus). Amphetamine produced little to no learning enhancement on our task but strongly influenced the conditioned response (CR), which peaked closer in time to the onset of the unconditioned stimulus (US). The overall ACC population response showed very weak stimulus-evoked modulations during the course of training, with the primary effect being an increase in inhibition. Group discrepancies in stimulus-invoked inhibition correlated with differences in learning performance, and this correlation was stronger when subjects were grouped according to learning performance, independent of drug treatment. ACC neuronal responses of both groups displayed hemispheric asymmetries (laterality), but amphetamine treatment altered this effect, in that activity within each hemisphere of the amphetamine group more closely resembled that of the contralateral hemisphere of controls. Our data suggest that amphetamine modulates CR timing, and influences the flow of sensory information to the two cortical hemispheres. Our observations are also consistent with the ACC's non-essential role in learning during delay eyeblink conditioning.

The lateral intraparietal area (LIP), a portion of monkey posterior parietal cortex, has been implicated in spatial attention. We review recent evidence showing that LIP encodes a priority map of the external environment that specifies the momentary locus of attention and is activated in a variety of behavioral tasks. The priority map in LIP is shaped by task-specific motor, cognitive and motivational variables, the functional significance of which is not entirely understood. We suggest that these modulations represent teaching signals by which the brain learns to identify attentional priority of various stimuli based on the task-specific associations between these stimuli, the required action and expected outcome.

It has long been known that the brain is limited in the amount of sensory information that it can process at any given time. A well-known form of capacity limitation in vision is the set-size effect, whereby the time needed to find a target increases in the presence of distractors. The set-size effect implies that inputs from multiple objects interfere with each other, but the loci and mechanisms of this interference are unknown. Here we show that the set-size effect has a neural correlate in competitive visuo-visual interactions in the lateral intraparietal area, an area related to spatial attention and eye movements. Monkeys performed a covert visual search task in which they discriminated the orientation of a visual target surrounded by distractors. Neurons encoded target location, but responses associated with both target and distractors declined as a function of distractor number (set size). Firing rates associated with the target in the receptive field correlated with reaction time both within and across set sizes. The findings suggest that competitive visuo-visual interactions in areas related to spatial attention contribute to capacity limitations in visual searches.

The lateral intraparietal area (LIP), a portion of monkey posterior parietal cortex, has been implicated in spatial attention. We review recent evidence from our laboratory showing that LIP encodes a priority map of the external environment that specifies the momentary locus of attention and is activated in a variety of behavioral tasks. The priority map in LIP is shaped by task-specific variables. We suggest that the multifaceted responses in LIP represent mechanisms for allocating attention, and that the attentional system may flexibly configure itself to meet the cognitive, motor and motivational demands of individual tasks.

Natural behavior requires close but flexible coordination between attention, defined as selection for perception, and action. In recent years a distributed network including the lateral intraparietal area (LIP) has been implicated in visuospatial selection for attention and rapid eye movements (saccades), but the relation between the attentional and motor functions of this area remains unclear. Here we tested LIP neurons in a task that involved not an ocular but a manual operant response. Monkeys viewed a display containing one cue and several distractors and reported the orientation of the cue (right- or left-facing) by releasing one of two bars grasped, respectively, with the right or left hand. The movement in this task thus was associated with (cued by), but not directed toward, the visual stimulus. A large majority of neurons responded more when the cue rather than when a distractor was in their receptive field, suggesting that they contribute to the attentional selection of the cue. A fraction of these neurons also was modulated by limb release, thus simultaneously encoding cue location and the active limb. The results suggest that the LIP links behaviorally relevant visual information with motor variables relevant for solving a task in a wide range of circumstances involving goal-directed or symbolically cued movements and eye as well as limb movements. A central function of the LIP may be to coordinate visual and motor selection during a wide variety of behaviors.