Abstracts

Rationale: The mesiotemporal lobe which is frequently affected in patients with temporal lobe epilepsy (TLE) was proposed to be crucial for decision processes since bilateral amygdala damage can cause impairments in decision making under ambiguity. In this kind of decision making, individuals have to choose between options without explicitly knowing the decision’s consequences and their probabilities. Therefore, the decision process mainly depends on the emotion-based processing of previously received consequences. Decision making under risk, in which explicit information about consequences and probabilities is available, was assumed to depend on executive functions in addition to the use of feedback. Although it is well known that patients with TLE frequently have unilateral mesiotemporal damage as well as impairments in functions associated with decision making (emotion processing, executive functioning), the ability to make decisions has not been investigated in these patients, to date. In the current study, we assessed whether TLE patients exhibit deficits in making decisions under ambiguity as well as under risk conditions. Methods: We presurgically examined 20 patients with unilateral refractory TLE and 20 healthy individuals (CG) with a task assessing decision making under ambiguity (Iowa Gambling Task, IGT), a task measuring decision making under risk (Game of Dice Task, GDT) and a neuropsychological test battery. Results: On the GDT patients did not differ from the CG (p=.26). On the IGT patients with TLE selected the disadvantageous alternatives more frequently compared to the CG (p=.03). A subgroup analysis revealed that those patients with disadvantageous decision making (n=11) had an earlier seizure onset (mean age of onset=12.14 years, SD=8.76) compared to those patients with advantageous decision making (n=11, mean age of onset =24.11 years, SD=12.87, p=.02). Executive subcomponents such as inhibition and cognitive flexibility were also lower in the group of patients deciding disadvantageously (p’s<.03). Decision making reductions occurred in five of six patients with selective unilateral hippocampal sclerosis not extended to the amygdala. Side of epileptogenic focus did neither impact GDT nor IGT performance (p’s>.62). Conclusions: Our results demonstrate for the first time that TLE patients can be selectively impaired in decision making under ambiguity that commonly depends on a feedback-driven emotional learning process. Patients with prepubertal age of onset and lower executive functioning seem to be at higher risk of having reductions in decision making; potentially due to the adverse effect of early seizures on the immature brain. Our results also give a first hint that selective, unilateral hippocampal damage without involvement of the amygdala may already cause a preference for disadvantageous decisions under ambiguous conditions. In contrast to decision making under ambiguity, TLE patients did not choose the disadvantageous options more frequently under risk conditions; most likely due to intact executive functioning in the patients studied.