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More Than Just Memories: Hippocampus Involved in Conflict Resolution

The hippocampus in the brain’s temporal lobe is responsible for more than just long-term memory. Researchers have for the first time demonstrated that it is also involved in quick and successful conflict resolution. The team headed by Dr. Nikolai Axmacher from the Ruhr-Universität Bochum (RUB), together with colleagues from the University Hospital of Bonn as well as in Aachen and Birmingham, reported in the journal Current Biology.

Decision conflicts occur often in everyday life

In their everyday life, people are constantly confronted with decision conflicts, especially if they need to suppress an action that would have made sense under normal circumstances. For example: when the pedestrian lights go green, a pedestrian would normally start walking. If, however, a car comes speeding along at the same time, the pedestrian should stay where he is. In their experiment, researchers opted for a less threatening situation. Test participants heard the words “high” or “low” spoken in a high or low tone, and they had to state – regardless of the meaning of the word – at what pitch the speaker said them. If the pitch doesn’t correspond with the meaning of the word, a conflict is generated: the participants would answer more slowly and make more mistakes.

Results confirmed with two measurement methods

The team demonstrated with two different measurement methods that the hippocampus is active in such conflicting situations; this applies particularly when a person solves the conflicts quickly and successfully. Nikolai Axmacher from the Institute of Cognitive Neuroscience and his colleagues analysed the brain activity in healthy participants with functional magnetic resonance imaging. They gained the same results in epilepsy patients who had EEG electrodes implanted in the hippocampus for the purpose of surgery planning; this is how the researchers could measure the activity in that brain region directly.

This image shows a brain with the hippocampus highlighted. In a thought bubble is an image of a person crossing a street.

The hippocampus is particularly active when a person solves conflicts quickly and successfully. Credit: RUB/Bierstedt.

Memory system could learn from resolved conflicts

Because the hippocampus is essential for memory, the researchers speculate about its role in conflict resolution: “Our data show first of all a completely new function of the Hippocampus – processing of activity conflicts,” says Carina Oehrn from the Department of Epileptology at the University Hospital of Bonn. “However, in order to answer the question how that function interacts with memory processes, we will have to carry out additional tests.” “Perhaps the memory system becomes particularly active if a conflict has been successfully resolved,” speculates Nikolai Axmacher. “Permanently unsolved conflicts can’t be used for learning helpful lessons for the future. According to our model, the brain works like a filter. It responds strongly to resolved conflicts, but not to unsolved conflicts or standard situations. However, we have to verify this hypothesis in additional studies.”

About this neuroscience research

Source: Dr. Nikolai Axmacher – Ruhr-Universität Bochum
Image Source: The image is credited to RUB/Bierstedt
Original Research: Abstract for “Human Hippocampal Dynamics during Response Conflict” by Carina R. Oehrn, Conrad Baumann, Juergen Fell, Hweeling Lee, Henrik Kessler, Ute Habel, Simon Hanslmayr, and Nikolai Axmacher in Current Biology. Published online August 20 2015 doi:10.1016/j.cub.2015.07.032


Abstract

Human Hippocampal Dynamics during Response Conflict

Highlights
•Hippocampal iEEG and BOLD activity increases during response conflicts in humans
•Hippocampal theta oscillations (3–8 Hz) predict behavioral performance
•Medial temporal conflict effects occur specifically in the hippocampus
•Our results suggest a role of the hippocampus beyond memory and spatial navigation

Summary
Besides its relevance for declarative memory functions [ 1–5 ], hippocampal activation has been observed during disambiguation of uncertainty and conflict [ 6, 7 ]. Uncertainty and conflict may arise on various levels. On the perceptual level, the hippocampus has been associated with signaling of contextual deviance [ 8–10 ] and disambiguation of similar items (i.e., pattern separation) [ 11–13 ]. Furthermore, conflicts can occur on the response level. Animal experiments showed a role of the hippocampus for inhibition of prevailing response tendencies and suppression of automatic stimulus-response mappings [ 14–17 ], potentially related to increased theta oscillations (3–8 Hz) [ 18 ]. In humans, a recent fMRI study demonstrated hippocampal involvement in approach-avoidance conflicts [ 19 ]. However, the more general significance of hippocampal activity for dealing with response conflicts also on a cognitive level is still unknown. Here, we investigated the role of the hippocampus for response conflict in the Stroop task by combining intracranial electroencephalography (iEEG) recordings from the hippocampus of epilepsy patients with region of interest-based fMRI in healthy participants. Both methods revealed converging evidence that the hippocampus is recruited in a regionally specific manner during response conflict. Moreover, our iEEG data show that this activation depends on theta oscillations and is relevant for successful response conflict resolution.

“Human Hippocampal Dynamics during Response Conflict” by Carina R. Oehrn, Conrad Baumann, Juergen Fell, Hweeling Lee, Henrik Kessler, Ute Habel, Simon Hanslmayr, and Nikolai Axmacher in Current Biology. Published online August 20 2015 doi:10.1016/j.cub.2015.07.032

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