Our brains are powerful prediction machines; whether it’s anticipating the next note in a familiar song or how hot your next sip of coffee will be, these predictions help us to make sense of our surroundings quickly and efficiently. However, exactly how these predictions are generated and communicated within the brain has so far been unclear.
The current study, published in Science Advances, used ultra-high-resolution functional magnetic resonance imaging (7T fMRI) in 30 healthy male and female participants to investigate how the hippocampus communicates with the sensory cortex.
Participants listened to sound cues that were linked to specific abstract shapes. The predicted shapes were shown in three-quarters of the trials but left out in the other quarter. This allowed the researchers to observe how brain activity changed when people expected to see a shape versus when they actually saw it.
The researchers found that when participants heard a sound cue, regions of the hippocampus, particularly CA2/3, and the parahippocampal cortex (PHC) showed distinct neural activity patterns.
The hippocampus is a region known for its role in memory and the CA2/3 subregions are heavily involved in associating different elements of an experience, making it a key brain area for predictive processing and pattern completion. The PHC on the other hand is a region of the brain that relays visual information between visual cortex and hippocampus.
Interestingly, these activity patterns were negatively correlated with the patterns seen when the same shape was presented without the sound cue. This suggests that the brain uses different neural codes for predicted versus unpredicted stimuli.
To understand the direction of communication between the hippocampus and the PHC, the team analysed activity across different cortical layers. Anatomical studies have revealed that superficial layers of PHC send signals to the hippocampus, whereas deep layers of PHC receive signals from the hippocampus. They found that communication of predictions between CA2/3 and PHC was specific to the deep layers of PHC. This supports the idea that memory and perception are tightly linked and that the hippocampus is not just a passive memory store, but an active generator of perceptual predictions.
The ability to study the direction of communication between the hippocampus and neocortex holds great promise for answering crucial questions in other domains of cognition as well, such as learning and memory, spatial navigation, and the use of cognitive maps.
Talking about the study, senior author, Professor Peter Kok, in the Department of Imaging Neuroscience, Queen Square Institute of Neurology said:
This study provides compelling evidence that the hippocampus is not just involved in remembering the past, but also in anticipating the future. By reconstructing expected sensory inputs and sending them to the PHC, it helps the brain anticipate what’s coming next. This predictive function may be essential not only for perception but for decision-making and learning.