The noradrenergic nucleus locus coeruleus (LC) is implicated in many cognitive functions, with activity tied to arousal and improvements in sensory and motor performance. These properties have motivated the hypothesis that the LC helps mobilize resources required for both action and cognition. Prior work established a strong link between LC activity and physical effort; this study directly tested whether LC activity causally supports cognitive effort using a reversible, cell-type–specific pharmacogenetic manipulation in nonhuman primates.
Authors used viral vectors to express inhibitory chemogenetic receptors (hM4Di DREADDs) selectively in noradrenergic LC neurons of two rhesus macaques. Reversible inhibition of LC neurons was achieved by systemic administration of the DREADD actuator deschloroclozapine (DCZ) at 0.1 mg/kg. A third monkey served as a control and received DCZ injections without DREADD expression. The design permitted within-subject, reversible suppression of LC activity in DREADD-expressing animals while controlling for systemic effects of the actuator in a non-DREADD animal.
Behavioral testing used a hole-board search task requiring monkeys to find hidden food rewards (raisins) in a 5×5 grid of wells. Two task conditions were interleaved or compared:
This contrast allowed the investigators to dissociate effects of LC inhibition on simple sensory-guided searching from effects on working-memory–dependent, effortful search strategies.
When rewards were visible (transparent condition), reversible LC inhibition produced no detectable change in performance. Measures that could index basic sensory-motor function and motivation—such as success in finding visible rewards and response times—were reported as unaffected by DCZ-induced suppression of LC in DREADD-expressing monkeys. This suggests that LC suppression did not broadly impair perception, motor execution, or willingness to perform the simple version of the task.
In the opaque condition, which required working memory to avoid revisiting empty wells, LC inhibition significantly impaired performance. The principal behavioral change was an increase in errors specifically characterized as revisits to wells already checked and found empty. Importantly, LC suppression did not reduce the overall number of rewards obtained, nor did it alter response times or apparent motivation. Instead, animals compensated for reduced success rate by performing more trials, indicating a decline in search efficiency rather than task abandonment or general motor slowing.
The pattern of effects—selective impairment in the cognitively demanding opaque condition, preserved performance in the transparent condition, unchanged response times and reward rate, and increased trial count to maintain reward intake—supports the interpretation that LC activity contributes to the mobilization of cognitive resources required for demanding search and working-memory use. The authors emphasize that the outcome reflects decreased efficiency in cognitive effort allocation rather than a reduction in motivation or engagement.
These findings provide causal evidence, in nonhuman primates, that LC activity supports cognitive effort and efficient deployment of working-memory–dependent search strategies. By extending pharmacogenetic causal manipulation to the primate LC, the study complements noninvasive human work linking noradrenergic function to cognitive control and effort. It also aligns with prior demonstrations of LC involvement in physical effort, suggesting a broader role for the noradrenergic system in resource mobilization across motor and cognitive domains.
The report summarized here is a preprint and has not been certified by peer review. The abstract describes two DREADD-expressing monkeys and one control animal receiving DCZ, but detailed methods, full statistical results, safety or off-target assessments, and sample-size justifications are not provided in the abstract. Where exact quantitative values, statistical tests, or additional methodological details are required, those were not reported in the source abstract and would need to be obtained from the full manuscript or subsequent peer-reviewed publication.
Note: The study authors declared no competing interests in the source document.