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 brain-wide interactions, particularly the patterns of neural activities giving rise to functions and behavior.   Now, a study from researchers at the University of Hong Kong shows low-frequency activity 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 the hippocampus should 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 (PNAS).

Previous studies show 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, resulting in early symptoms such as short-term memory loss or disorientation.  However, the role of the hippocampus in complex brain networks, particularly its influence on brain-wide functional connectivity, is not well understood.  The current study shows low-frequency activity propagates in the dorsal hippocampal–cortical pathway, to drive interhemispheric cortical rsfMRI connectivity, and mediate visual processing.

The current study utilizes 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 low-frequency activities in the hippocampus drive brain-wide functional connectivity in the cerebral cortex and enhance sensory responses.  Data findings show low-frequency activities of the hippocampus drive the functional integration between different regions of the cerebral cortex and enhance the responsiveness of vision, hearing, and touch.

Results show low-frequency activities in the hippocampus can enhance learning and memory as these activities usually occur during slow-wave sleep.  The lab states it could reasonably be expected for the hippocampus to generate high-frequency activities, however, their data indicates low-frequency optogenetic excitation of the dorsal dentate gyrus evokes cortical and subcortical activities.

The team surmises their study highlights the important role of slow-wave activity in the hippocampal–cortical region in driving brain-wide connectivity and mediating sensory processing. For the future, the researchers state their findings signify the potentials of rsfMRI and neuromodulation for early diagnosis and enhanced treatment of brain diseases including dementia and PTSD.

Source: University of Hong Kong

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