Functional MRI of long-term potentiation: imaging network plasticity

Abstract

Neurons are able to express long-lasting and activity-dependent modulations of their synapses. This plastic property supports memory and conveys an extraordinary adaptive value, because it allows an individual to learn from, and respond to, changes in the environment. Molecular and physiological changes at the cellular level as well as network interactions are required in order to encode a pattern of synaptic activity into a longterm memory. While the cellular mechanisms linking synaptic plasticity to memory have been intensively studied, those regulating network interactions have received less attention. Combining high-resolution fMRI and in vivo electrophysiology in rats, we have previously reported a functional remodelling of long-range hippocampal networks induced by long-term potentiation (LTP) of synaptic plasticity in the perforant pathway. Here, we present new results demonstrating an increased bilateral coupling in the hippocampus specifically supported by the mossy cell commissural/ associational pathway in response to LTP. This fMRI-measured increase in bilateral connectivity is accompanied by potentiation of the corresponding polysynaptically evoked commissural potential in the contralateral dentate gyrus and depression of the inactive convergent commissural pathway to the ipsilateral dentate. We review these and previous findings in the broader context of memory consolidation.

Targeted enhancement of cortical-hippocampal brain networks and associative memory

“…fMRI connectivity changes due to stimulation could reflect LTP-like effects throughout cortical-hippocampal networks (20). Indeed, changes were evident ~24 hours after stimulation (Post-Tx), indicating long-term plasticity.…”

Tuning noninvasive brain stimulation with MRI to cope with intersubject variability

“…Apart from the systems-level implications of these results for memory formation, they already demonstrated the important influence of local synaptic plasticity on activity propagation in brain-wide networks. Furthermore, the potentiation of neuronal responses, indicated by the steepened slope of the population excitatory postsynaptic potentials and the increased amplitude of the population spikes, correlated with the amplitude of the blood oxygen level-dependent signal, thus validating the usefulness of MRI for assessing global plasticity changes [51]. In contrast to detecting the effects elicited by noninvasive stimulation protocols only by means of their final parameters and comparing those to the corresponding datasets gathered prior to NIBS or rSS, a coupled on-going monitoring of stimulation effects is probably the more advantageous alternative.…”

“…A pioneer study combining simultaneously fMRI with intracranial electrophysiological recordings and deep brain stimulation in rats was conducted to investigate the influence of local synaptic plasticity on long-range functional connectivity in the brain [50][51][52]. In this work, induction of LTP by high-frequency stimulation of the perforant pathway connecting the medial entorhinal cortex with the dorsal hippocampus resulted in brain-wide reorganization of neuronal networks.…”

Combining Exergame Training with Omega-3 Fatty Acid Supplementation: Protocol for a Randomized Controlled Study Assessing the Effect on Neuronal Structure/Function in the Elderly Brain

“…Moreover, TMS is used in this study as an indirect proxy measure of synaptic plasticity. Based on the results of this study future studies should focus on more direct measures of synaptic plasticity by using either magnetic resonance tomography (Alvarez-Salvado et al, 2014) or positron emissions tomography scans (Magistretti, 2006) for comparing the brain scans before and after the intervention.…”