Concurrent Physiological Multisite-Recordings & Brain Imaging: Study of Dynamic Connectivity Related to System and Synaptic Memory Consolidation

  • Nikos K. Logothetis


Experimental work in animals and humans suggests that various short-lasting patterns of neural activity, including single- or multiple-cycle oscillatory episodes, may reflect state changes of self-organizing large- scale networks. Such state-marking events, including K complexes, spindles, hippocampal sharp wave ripples (SPW-R), and ponto-geniculo-occipital (PGO) waves, are in fact thought to regulate cognitive capacities, such as learning, memory encoding and consolidation, as well as memory-guided decision making.

Although the neural events themselves have long been studied in great detail with neurophysiological methods, the actual brain-states related to them remain elusive, primarily due to a dearth of methodologies permitting concurrent recordings in various structures and mapping of whole-brain activity. The use of multishank-multichannel (MS-MC) electrical recordings of activity in different structures per se permits both the detection and the contextual identification of structure-specific neural events, for that matter also of their interrelationships. Combining in real-time the MS-MC recordings with spatiotemporally resolved functional magnetic resonance imaging (fMRI) evidently offers a unique opportunity to study the cooperative patterns of a large number of brain structures either leading or responding to recorded events. In an effort to map and study such patterns, we have recently developed so-called neural event triggered fMRI (NET-fMRI) and used it to understand the dynamics of the networks related to SPW-R and PGO events, both considered to be critical for the sequential states of system and synaptic memory consolidation during sleep.

The observed neurophysiological interactions of hippocampus, thalamus, cortex and pontine nuclei, together with the maps of robust up/down modulation of the brainwide metabolic activity revealed both synergistic and strong antagonistic interactions between memory systems, as well as between the activities of sensory thalamic and neuromodulatory nuclei and the hippocampal formation during epochs potentially related to memory consolidation. On-going work is currently examining the event-triggered neurophysiological responses in a number of structures, mapped with imaging, as well as the extent to which fMRI-measured multistructure activity patterns at any given time may themselves predict the occurrence of various neural events.