Having applied new neurocognitive and mathematical approaches, a group of Russian scientists with the participation of MEPhI has described an interaction between hippocampus and other important areas of human brain for the first time. The results of work have been published in journal Frontiers in Human Neuroscience.

Scientists have researched hippocampus, a conjugated structure in medial crotaphic parts of cerebral hemispheres, connected with processes of remembrance and orientation in space.

The gist of work was in studying of cause-and-effect (or effective) connections between left and right hippocampal regions of a human with main structures of the network of passive mode of brain work (Default Mode Network), which operates brain work in the awake resting state, basic condition of human conscience. Defaulted mode network includes medial prefrontal cortex (MPFC), posterior cingulate cortex (PCC), and the inferior parietal cortex of left (LIPC) and right (RIPC) hemispheres. These two structures unite intermodal (visual, audial, vestibular, and tactile) information about opposite half of egocentric spatial environment: LIPC – about right semispace, and RIPC – about left semispace.

30 healthy subjects took part in the research (10 males and 20 females), all right-handed, of age from 20 to 35 years. In the resting state the data of the participants’ functional magnetic resonance tomography (FMRT) was recorded. To calculate effective relationships, the mathematical method of spectral dynamic causal modeling (DCM) was used. The main idea of ​​this method is to evaluate the parameters of a biologically based model of brain neural network interaction so that it best predicts the FMRT data, observed in the experiment.

Scientists conducted three DCM analyzes, verifying in total predictions of about 3,000 quantitative models. The first two analyzes allowed identify interactions between areas that included four key structures of the passive brain network in addition to the left and right hippocampus. The third analysis was a virtual neurosurgical experiment to determine the consequences, that "removal" of one of the key structures of the human brain (PCC) might have, for the work of hippocamps and interferences within the default neural network.

The study of effective (cause-effect) connections of both human hippocampus with other important structures of the brain was carried out for the first time. "We found evidence of a pronounced asymmetry in the work of the left and right hippocampus, which was completely unknown from studies, conducted on animals. In general, the left hippocampus is more active than the right, interacting with the rest of the brain structures. Apparently, this is due to the fact that speech mechanisms in humans (in 97% of right-handers and 75% of left-handers) are localized in the left hemisphere. But the right hippocampus has its advantage: it receives information from both intermodal centers, LIPC and RIPC, which serves as the basis for a holistic view of the environment. The left hippocampus, on the other hand, receives information only from the LIPC, so its "knowledge" about the environment is limited to the right "half-space", said project manager Boris Velichkovsky.

"With the participation of MEPhI scientists, an analysis of effective connections was made that allows us to determine the architecture of neural networks," said Vadim Ushakov, senior research fellow at the Department of Cybernetics of MEPhI ICIS, leading researcher at the Research Center "Kurchatov Institute".

He noted that such asymmetry of effective hippocampal connections explains one of the most frequent disorders of consciousness, observed in the clinic of local brain lesions, namely, left-sided space hemineglect in patients with lesions of the right hemisphere. A patient with such a defeat at meal ignores the food located on the left side of the plate, or, preparing for medical examination, shaves only the right half of the face. As a rule, traumas of the left hemisphere do not lead to similar loss of perception of the right half of the environment.

According to Vadim Ushakov, the study allows for a more holistic understanding of the work of the neural networks of the brain in order to provide a basic level of consciousness, in medical practice this serves as a good help for an accurate diagnosis of the functionality of the brain.

The research was attended by scientists from the Moscow State University, Kurchatov Institute, MEPhI, Higher School of Economics, Russian State University for the Humanities, and Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences. The study is supported by the Russian Science Foundation.