Men tend to have greater positive responses than women to explicit visual erotic stimuli (EVES). However, it remains unclear, which brain network makes men more sensitive to EVES and which factors contribute to the brain network activity. In this study, we aimed to assess the effect of sex difference on brain connectivity patterns by EVES. We also investigated the association of testosterone with brain connection that showed the effects of sex difference. During functional magnetic resonance imaging scans, 14 males and 14 females were asked to see alternating blocks of pictures that were either erotic or non-erotic. Psychophysiological interaction analysis was performed to investigate the functional connectivity of the nucleus accumbens (NA) as it related to EVES. Men showed significantly greater EVES-specific functional connection between the right NA and the right lateral occipital cortex (LOC). In addition, the right NA and the right LOC network activity was positively correlated with the plasma testosterone level in men. Our results suggest that the reason men are sensitive to EVES is the increased interaction in the visual reward networks, which is modulated by their plasma testosterone level.

14Depression is characterized by deficits in the reinforcement learning (RL) process. Although

Dopamine activity may transition between two patterns: phasic responses to reward-predicting cues and ramping activity arising when an agent approaches the reward. However, when and why dopamine activity transitions between these modes is not understood. We hypothesize that the transition between ramping and phasic patterns reflects resource allocation which addresses the task dimensionality problem during reinforcement learning (RL). By parsimoniously modifying a standard temporal difference (TD) learning model to accommodate a mixed presentation of both experimental and environmental stimuli, we simulated dopamine transitions and compared it with experimental data from four different studies. The results suggested that dopamine transitions from ramping to phasic patterns as the agent narrows down candidate stimuli for the task; the opposite occurs when the agent needs to re-learn candidate stimuli due to a value change. These results lend insight into how dopamine deals with the tradeoff between cognitive resource and task dimensionality during RL.

148 WORDS) 2 5Humans recall the past by replaying fragments of events temporally. Here, we 2 6 demonstrate a similar effect in macaques. We trained six rhesus monkeys with a 2 7 temporal-order judgement (TOJ) task and collected 5000 TOJ trials. In each trial, they 2 8 watched a naturalistic video of about 10 s comprising two across-context clips, and 2 9 after a 2-s delay, performed TOJ between two frames from the video. The monkeys 3 0 apply a non-linear forward, time-compressed replay mechanism during the 3 1 temporal-order judgement. In contrast with humans, such compression of replay is 3 2 however not sophisticated enough to allow them to skip over irrelevant information 3 3 by compressing the encoded video globally. We also reveal that the monkeys detect 3 4 event contextual boundaries and such detection facilitates recall by an increased rate 3 5 of information accumulation. Demonstration of a time-compressed, forward replay 3 6 like pattern in the macaque monkeys provides insights into the evolution of episodic 3 7 memory in our lineage. 3 8 3 9