Study identifies new function for the hippocampus.


The human brain is the source of a person’s thoughts, emotions, perceptions, actions, and memories.  One challenge for neuroscience is to achieve an integrated understanding of the large-scale brain-wide interactions, particularly the patterns of neural activities that give rise to functions and behaviour.   Now, a study from researchers at the University of Hong Kong shows that low-frequency activity robustly propagates in the dorsal hippocampal–cortical pathway, to drive interhemispheric cortical resting-state fMRI (rsfMRI) connectivity, and mediate visual processing.  The team states their data indicates that the hippocampus can be considered as the heart of the brain, a breakthrough in the knowledge of how the brain works.   The opensource study is published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

Previous studies show that the hippocampus, located underneath the cortex, plays an important role in memory and navigation. Alzheimer’s disease and other forms of dementia have been proven to affect and damage this area of the brain, resulting in early symptoms such as short-term memory loss and disorientation.  However, the role of hippocampus in complex brain networks, particularly its influence on brain-wide functional connectivity, is not well understood.  The current study shows that low-frequency activity robustly propagates in the dorsal hippocampal–cortical pathway, to drive interhemispheric cortical rsfMRI connectivity, and mediate visual processing.

The current study utilises optogenetics and fMRI to investigate how excitatory neural activity initiated in the dorsal dentate gyrus of the hippocampus propagates and modulates rsfMRI connectivity.  Results show that low-frequency activities in the hippocampus drive brain-wide functional connectivity in the cerebral cortex and enhance sensory responses.  Data findings show that low-frequency activities of the hippocampus drives the functional integration between different regions of the cerebral cortex and enhance the responsiveness of vision, hearing and touch.

Results show that low-frequency activities in the hippocampus can enhance learning and memory since low-frequency activities usually occur during slow-wave sleep which has been associated with learning and memory.  The lab state that based on current knowledge, one expects the hippocampus to predominantly generate high-frequency activities and these activities are largely confined within the hippocampus; however, in their study, low-frequency optogenetic excitation of the dorsal dentate gyrus, a subregion of the hippocampus, evoked cortical and subcortical activities which are beyond the hippocampus.

The team surmise their study highlights the important role of slow hippocampal–cortical activity in driving brain-wide connectivity and mediating sensory processing. For the future, the researchers state that their findings signify the potentials of rsfMRI and neuromodulation for early diagnosis and enhanced treatment of brain diseases including Alzheimer’s disease, dementia, epilepsy, schizophrenia, transient global amnesia, and PTSD.

Source:University of Hong Kong

 

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