Summary: Researchers reveal specific parts of the hippocampus may play a key role in emotional regulation.
Source: University of Toronto.
The hippocampus is an area of the brain commonly linked with memory and dementia.
But new U of T Scarborough research finds that it may also yield important clues about a range of mental health illnesses including addiction, anxiety and depression.
The research, authored by a team of neuroscientists, found that a specific part of the hippocampus could play an important role in emotional regulation, a finding that calls into question our understanding of how exactly this part of the brain works.
“What this shows is that we may need to rethink how the hippocampus processes information,” says Rutsuko Ito, an associate professor in the Department of Psychology.
The hippocampus is a seahorse-shaped structure located deep inside the brain. As part of the limbic system, it plays an important role in memory processing and spatial cognition, including how mammals learn to understand and navigate their environment.
Researchers have long looked at the hippocampus for its role in memory and dementia, especially in relation to Alzheimer’s disease. In Alzheimer’s patients for instance, this region is one of the first areas of the brain to suffer damage.
But there’s been a few studies that suggest the anterior hippocampus, a sub-region located at the front, could play a role in emotional regulation, including anxiety.
For this study, Ito and her team looked at the ventral hippocampus in rats, a sub-region that correlates to the anterior hippocampus in humans. They wanted to see what role two further subareas of the ventral hippocampus — called the CA1 and CA3 — play in terms of approach-avoidance conflict processing.
Approach-avoidance conflict is a model used in psychology to test how animals deal with regulating fear and anxiety. It basically offers a situation that involves a decision about whether to pursue or avoid something that could have both positive and negative aspects to it.
“One good example is imagine going to a restaurant you love, but the moment you walk in you see someone you can’t stand – do you go in, or avoid going in?” says Associate Professor Andy Lee, who collaborated on the research.
What they found is that after temporarily inactivating the CA1, it increased avoidance of the conflict. Meanwhile, inactivating the CA3 increased approach behaviour to the conflict.
Ito says this finding is important because the conventional thinking is that these areas, along with another part called the dentate gyrus, form a circuit through which information flow occurs in one direction. Information processed by the dentate gyrus gets passed along to the CA3, and then on to CA1. In other words, the CA1 and CA3 should carry out the same function because they’re both part of the same information processing circuit.
“But that’s not the case, the CA1 and CA3 in the ventral hippocampus seem to do very opposite things in relation to conflict processing,” says Ito.
“It’s this strange bi-directional or oppositional effect, and that goes against traditional thinking of how information processing takes place in this part of the brain,” she says.
Because of its possible role in basic motivational behaviour, it may also offer important insights into a range of mental health illnesses. Addiction, for example, could be linked to deficits of approach motivation. Anxiety and depression on the other hand could be linked to avoidance behaviours, all of which could manifest itself in this part of the brain.
The research, which was published in the journal Current Biology, received funding from the Natural Sciences and Engineering Research Council of Canada, and the Canada Institutes for Health Research.
Ito says the next step is to explore which connections to the CA1, CA3, or other parts of the brain could be responsible for this effect.
Meanwhile, Lee is investigating the role sub-regions of the hippocampus play in conflict processing in humans.
“Some patients have lesions to certain areas of this part of the brain, so hopefully we can assess them to see what particular aspects of approach avoidance behaviour may or may not be impacted,” he adds.
Funding: Natural Sciences and Engineering Research Council of Canada, Canadian Institutes for Health Research funded this study.
Source: Don Campbell – University of Toronto
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Open access research for “Ventral Hippocampal CA1 and CA3 Differentially Mediate Learned Approach-Avoidance Conflict Processing” by Anett Schumacher, Franz R. Villaruel, Alicia Ussling, Sadia Riaz, Andy C.H. Lee, and Rutsuko Ito in Current Biology. Published March 28 2018.
Ventral Hippocampal CA1 and CA3 Differentially Mediate Learned Approach-Avoidance Conflict Processing
•Rats underwent a cue-based learned approach-avoidance conflict paradigm
•Ventral CA3 inactivation increased approach behavior to a conflict cue
•Ventral CA1 inactivation induced increased avoidance of the conflict cue
•Hippocampal subfields play distinct roles in learned approach-avoidance conflict
Approach-avoidance conflict arises when an animal encounters a stimulus that is associated simultaneously with positive and negative valences. The effective resolution of approach-avoidance conflict is critical for survival and is believed to go awry in a number of mental disorders, such as anxiety and addiction. An accumulation of evidence from both rodents and humans suggests that the ventral hippocampus (anterior in humans) plays a key role in approach-avoidance conflict processing, with one influential model proposing that this structure modulates behavioral inhibition in the face of conflicting goals by increasing the influence of negative valences. Very little is known, however, about the contributions of specific hippocampal subregions to this process—an important issue given the functional and anatomical heterogeneity of this structure. Using a non-spatial cue-based paradigm in rats, we found that transient pharmacological inactivation of ventral CA1 produced an avoidance of a conflict cue imbued with both learned positive and learned negative outcomes, whereas inactivation of the ventral CA3 resulted in the opposite pattern of behavior, with significant preference for the conflict cue. In contrast, dorsal CA1- and CA3-inactivated rats showed no change in conflict behavior, and furthermore, additional behavioral tasks confirmed that the observed pattern of approach-avoidance findings could not be explained by other factors, such as differential alterations in novelty detection or locomotor activity. Our data demonstrate that ventral CA1 and CA3 subserve distinct and opposing roles in approach-avoidance conflict processing and provide important insight into the functions and circuitry of the ventral hippocampus.