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C6 - Neural correlates of intact and impaired PFC-HC interactions during HC-dependent cognitive functions

Principal investigator(s):

Institut für Neuropsychologie und Klinische Psychologie
Zentralinstitut für Seelische Gesundheit (ZI)
J5, D-68159 Mannheim

Tel.:
+49-621-1703-6302
Fax:
+49-621-1703-6305
Internet:
http://www.zi-mannheim.de
Email:
herta.flor@zi-mannheim.de

Institut für Neuropsychologie und Klinische Psychologie
Zentralinstitut für Seelische Gesundheit (ZI)
J5, D-68159 Mannheim

Tel.:
+49-621-1703-6314
Fax:
+49-621-1703-6305
Internet:
http://www.zi-mannheim.de
Email:
carsten.diener@zi-mannheim.de

Projects within the BCCN:


The subproject C6 used two different experimental paradigms (contextual fear conditioning, a source memory task) and two different brain imaging modalities (functional magnetic resonance imaging (fMRI), electroencephalography (EEG)) to address questions regarding episodic memory functioning in subjects with purported hippocampal impairment compared to healthy controls. In the first investigation (Baeuchl et al. 2015), we developed a differential contextual conditioning paradigm, which requires configural context processing for successful associative learning. This was achieved by employing the same cue-elements in two contexts and only varying the composition of those cues between contexts, which necessitates memorizing the cue-configuration in order to distinguish them, a process that is believed to be hippocampus-dependent. Using this paradigm, we examined differences in fear learning of old healthy adults, depressive patients and schizophrenic patients compared to young healthy controls during fMRI. We could show that even among young healthy controls, subjects who do not develop awareness of the CS/US contingency show no differential learning-related autonomous responses, no fear-related brain activity and have worse performances in tests on visual and working memory. A further comparison between young and old healthy adults showed that a larger number of older adults were contingency unaware and had higher activation in the hippocampus than young adults, a potential overcompensation mechanism in the old-age group which is impaired in configural context processing. In the second investigation, a spatial source memory task was employed, in which subjects were required to memorize the position of objects in one of four squares on a screen while EEG was recorded from healthy young, healthy old and depressive subjects. It was hypothesized that compared to young adults, depressive patients and older adults would show deficient source monitoring processes, which would be reflected in a delay of correct source allocations and a reduction of the parietal old/new effect. The comparison between old and young subjects revealed no significant late parietal old/new effect in old subjects, related to recollection when successful source retrieval was contrasted with source retrieval failure. A late frontal positivity related to source monitoring was not found in old subjects either, while both effects could be detected in young adults. These results were accompanied by reduced source retrieval performance in old subjects. Taken together with the results from the previous EEG-fMRI study (Hoppstädter et al. 2015), where the parietal old/new effect was linked to hippocampal activity, we can infer from our study that old subjects\' reduced source memory performance is due to a deficient fronto-hippocampal network.
The results of the first study demonstrate the importance of contingency awareness for contextual fear conditioning and shed light on potential mechanisms for contingency learning for paradigms which use difficult-to-discriminate context stimuli that require configural processing. Future contextual conditioning studies need to take contingency awareness and differences in visual working memory capacity into account when examining individual differences in the acquisition of contextual fear. A more thorough understanding of how contingency awareness can facilitate or inhibit implicit associations might be critical for treating anxiety disorders. Concerning the second study, further studies need to clarify whether the deficiency of old subjects comes from retrieval problems or whether there are already shortcomings at the level of encoding. If the location of the deficit can be narrowed down, neurocognitive trainings could be designed and evaluated in a new aging population. The desired outcome would be trainings that are ecologically valid and suitable for daily use to overcome source memory problems that can substantially affect daily life in old age.

Key publications:

Baeuchl C, Meyer P, Hoppstadter M, Diener C, Flor H (2015) Contextual fear conditioning in humans using feature-identical contexts Neurobiol Learn Mem, 121:1-11 .
Hoppstädter M, Baeuchl C, Diener C, Flor H, Meyer P (2015) Simultaneous EEG and fMRI reveals the brain networks underlying recognition memory ERP old/new effects Neuroimage,116:112-122 .