Hippocampal function during associative learning in patients with posttraumatic stress disorder

Abstract

In the last decade several studies have shown memory deficits in patients with posttraumatic stress disorder (PTSD) which have been associated with a reduced hippocampus volume. However, until now we do not know how or whether these structural abnormalities turn into functional abnormalities. Thus, the primary purpose of the present study was the investigation of the hippocampal function using functional magnet resonance imaging (fMRI). We compared PTSD patients and healthy control participants using an associative learning paradigm consisting of two encoding and one retrieval condition. During fMRI scanning participants had to learn face-profession pairs. Afterwards only faces were presented as cue stimuli for associating the category of the prior learned target profession and the participants had to decide whether this face belonged to a scientific or an artistic profession. Additionally, cognitive functioning, i.e. memory and attention, was examined using neuropsychological standard tests. During encoding PTSD patients showed stronger hippocampal and weaker prefrontal activation compared to healthy control participants. During retrieval the two groups did not differ neither in hippocampus activation nor in accuracy of retrieval. PTSD patients however showed a reduced activation in the left parahippocampal gyrus and other memory-related brain regions. We did not find any significant memory differences between PTSD patients and healthy control participants. The results suggest that PTSD has an effect on memory-related brain function despite intact memory functioning. In particular the hippocampal/parahippocampal regions and the prefrontal cortex show functional alterations during associative learning and memory.