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Focal Human CA1 Lesion Potentiates Avoidance Behaviour During Approach-Avoidance Conflict Decision-Making

Poster Session A - Saturday, March 7, 2026, 3:00 – 5:00 pm PST, Fairview/Kitsilano Ballrooms

Willem Le Duc¹, Rutsuko Ito¹, Andy Lee^1,2; ¹University of Toronto Scarborough, ²Rotman Research Institute, Bacyrest Centre, Toronto, Canada

Approach-avoidance conflict (AAC) occurs when a goal stimulus is associated with both rewarding and aversive outcomes simultaneously, and an organism must resolve competing tendencies to engage with or evade it. Rodent work has implicated the ventral hippocampus (vHPC) in resolving AAC: gross vHPC lesions have been shown to potentiate approach behaviour, and selective inactivation of the CA1 or CA3 subfields within the vHPC result in increased avoidance and approach behaviour, respectively. Human patient studies have similarly shown that large anterior HPC (aHPC; the human vHPC analogue) lesions result in greater approach behaviour under motivational conflict. However, there has been no human patient work investigating the roles of subfields within the aHPC, as in rodents. In the current study, we recruited a patient with a focal CA1 lesion (female; age = 43) and 12 controls (all female; age: M = 42.46, SD = 3.07). We administered an AAC task to all participants, in which they first learned to associate individual images with either reward or punishment, and were later asked to approach or avoid combined pairs of these images, with pairs with conflicting outcomes designed to elicit AAC. Consistent with prior rodent research, the CA1 patient was significantly more avoidant than controls under conflict, a difference that was not attributable to differences in learning rates of stimulus valences. These findings provide causal evidence that rodent hippocampal subfield-specific AAC behavioural findings extend to humans and furthers our understanding of the role of the HPC in resolving AAC.

Topic Area: THINKING: Decision making