No abstract

The involvement of the human amygdala in emotion-related processing has been studied using functional magnetic resonance imaging (fMRI) for many years. However, despite the amygdala being comprised of several subnuclei, most studies investigated the role of the entire amygdala in processing of emotions. Here we combined a novel anatomical tracing protocol with eventrelated high-resolution fMRI acquisition to study the responsiveness of the amygdala subnuclei to negative emotional stimuli and to examine intra-amygdala functional connectivity. The greatest sensitivity to negative emotional stimuli was observed in the centromedial amygdala, where the hemodynamic response amplitude elicited by negative emotional stimuli was greater and peaked later than for neutral stimuli. Connectivity patterns converge with extant findings in animals, such that the strongest connectivity was between the lateral nucleus and the nuclei of the basal amygdala. Current findings provide evidence of functional specialization within the human amygdala.

The functional role of the hippocampal formation in episodic memory has been studied using functional magnetic resonance imaging (fMRI) for many years. The hippocampus can be segmented into three major anteroposterior sections, called head, body and tail, and into the Cornu Ammonis (CA), dentate gyrus (DG), and subiculum (Sub) subfields based on its transverse axis. However, the exact role of these subregions and subfields in memory processes is less understood. In the present study we combined ultra-high resolution structural Magnetic Resonance Imaging (MRI) at 4.7 T with an event-related high-resolution fMRI paradigm based on the 'Designs' subtest of the Wechsler Memory Scale to investigate how the hippocampal subfields and longitudinal subregions are involved in encoding and retrieval of item, spatial, and associative memories. Our results showed that during memory encoding, regardless of the type of memory being learned, all subregions and all subfields were active. During the retrieval phase, on the other hand, we observed an anterior to posterior gradient in hippocampal activity for all subfields and all types of memory. Our findings also confirmed presence of an anterior to posterior gradient in hippocampal activity during spatial learning. Comparing subfield activities to each other revealed that the DG was more active than the CA1-3 and Sub during both encoding and retrieval. Finally, our results showed that for every subfield, encoding vs. retrieval activity differences were larger in the hippocampal head than in the hippocampal body and tail. Furthermore, these encoding vs. retrieval activity differences were similar in all subfields, highlighting the importance of studying both the longitudinal and transverse axis specialization simultaneously. Current findings further elucidate the structure-function relationship between the human hippocampus and episodic memory. Highlights• Hippocampus responded similarly during item, spatial, and associative learning • The entire hippocampus was active during memory encoding• Retrieval activity was characterized by an anterior to posterior gradient • Dentate gyrus showed the largest BOLD activity during both encoding and retrieval• Both the longitudinal and transverse properties characterize hippocampal function