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This study is the physiological complement to previous behavioral work that demonstrated that rhesus monkeys are able to allocate attention about the surrounding space based on brief, broadband auditory cues. Single-unit recordings were taken from the intermediate layers of the superior colliculus (iSC) while the subjects oriented to visual and auditory targets in the context of a cuing task with their heads unrestrained. The results show a correlation between behavioral manifestations of attention allocation, attention capture and inhibition of return, and modulation of target-evoked responses in single iSC neurons. NEW & NOTEWORTHY These results show for the first time a neural correlate of attention capture and inhibition of return in response to auditory stimuli in the superior colliculus of the head-unrestrained monkey.

Decisions are often made based on which option will result in the largest reward. When given a choice between a smaller but immediate reward and a larger delayed reward, however, humans and animals often choose the smaller, an effect known as temporal discounting. Dopamine (DA) neurotransmission is central to reward processing and encodes delayed reward value. Impulsivity, the tendency to act without forethought, is associated with excessive discounting of rewards, which has been documented in patients with attention deficit hyperactivity disorder (ADHD). Both impulsivity and temporal discounting are linked to the dopaminergic system. Methylphenidate (MPH), which blocks the DA transporter and increases extracellular levels of DA in the basal ganglia and prefrontal cortex, is a primary treatment for ADHD and, at low doses, ameliorates impulsivity in both humans and animals. This study tested the hypothesis that low doses of MPH would decrease the discounting rate of rhesus monkeys performing an intertemporal choice task, suggesting a reduction in impulsivity. The results support this hypothesis and provide further evidence for the role of DA in temporal discounting and impulsive behavior.

Several auditory spatial illusions, collectively called the precedence effect (PE), occur when transient sounds are presented from two different spatial locations but separated in time by an interstimulus delay (ISD). For ISDs in the range of localization dominance (

Impulsivity, the predisposition to act without regard for negative consequences, is a characteristic of several psychiatric disorders and is thought to result in part from genetic variation in the untranslated region of the dopamine transporter (DAT) gene. As the exact link between genetic mutations and impulsivity has not been established, we used oculomotor behavior to characterize rhesus monkeys as impulsive or calm and genetic/epigenetic analysis and positron emission tomography (PET) to correlate phenotype to DAT genotype, DAT gene methylation, and DAT availability. We found three single nucleotide polymorphisms (SNPs) in the 3′-UTR of the DAT gene, one of which provided a potential site for methylation in the impulsive group. Bisulfite analysis showed that the DNA of the impulsive but not the calm subjects was methylated at one SNP. Because genetic/epigenetic modifications could lead to differences in protein expression, we measured DAT availability using [18F]2β-carbomethoxy-3β-(4-chlorophenyl)-8-(2-fluoroethyl)-nortropane ([18F]FECNT) PET and found higher DAT availability in the internal globus pallidus, an output nucleus of the basal ganglia, of the impulsive group. Higher DAT availability lowers dopamine levels, potentially altering neuronal circuits involved in the initiation of action, thus contributing to the impulsive phenotype. The association between increased methylation in the DAT gene and greater DAT availability suggests that mutations to the regulatory portion of the DAT gene lead to a susceptibility to epigenetic modification resulting in a discrete behavioral phenotype.

Operant conditioning was used to train cats with their heads immobilized to localize sound by directing their eyes to the location of the sources. The kinematics of those eye movements were studied and compared with eye movements to visual targets at the same locations. The main finding of this study is that eye movements to broadband long-duration acoustic targets have two components: an initial slow phase of variable duration and a fast, normal saccade. The slow component is characterized by a persistent, shallow velocity ramp, while the saccadic component of the response falls on the main sequence computed from eye movements to visual targets. The slow component was shorter before saccades to long-duration stimuli performed under the delayed-saccade task and practically absent before saccades to transient acoustic stimuli. The results suggest that the initial slow component is used by cats to deal with uncertainty associated with the location of long-duration broadband targets and that the input to the saccade integrator(s) is similar under both visual and acoustic conditions.