A network approach for modulating memory processes via direct and indirect brain stimulation: Toward a causal approach for the neural basis of memory

Abstract

A network approach for modulating memory processes via direct and indirect brain stimulation: Toward a causal approach for the neural basis of memory This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. that disrupting frontal or parietal regions also impairs memory performance, suggesting that these regions also play necessary roles in declarative memory. On the other hand, a handful of both invasive and non-invasive studies have also suggested modest improvements in memory performance following stimulation. These studies typically target brain regions connected to the hippocampus or other memory "hubs," which may affect endogenous activity in connected areas like the hippocampus, suggesting that to augment declarative memory, altering the broader endogenous memory network activity is critical. Together, studies reporting memory improvements / impairments are consistent with the idea that a network of distinct brain "hubs" may be crucial for successful memory encoding and retrieval rather than a single primary hub such as the hippocampus. Thus, it is important to consider neurostimulation from the network perspective, rather than from a purely localizationalist viewpoint. We conclude by proposing a novel approach to neurostimulation for declarative memory modulation that aims to facilitate interactions between multiple brain "nodes" underlying memory rather than considering individual brain regions in isolation.

Direct Electrical Stimulation of the Human Entorhinal Region and Hippocampus Impairs Memory

“…Nonetheless, it may be possible to learn from our results to derive more effective stimulation protocols. Our findings support the general approach of choosing the entorhinal region and hippocampus as stimulation targets for memory modulation by showing that these sites are part of a network that can be used to causally modulate memory (Kim et al, 2016). However, going forward to achieve memory improvement it may be helpful to refine the types of stimulation parameters that are used, perhaps by measuring ongoing brain activity or by refining stimulation targets on the basis of individualized interregion connectivity patterns (Wang et al, 2014).…”

“…Although memory is a complex process that involves widespread brain regions (Squire, 1992;Kim et al, 2016), these findings provide key additional evidence that the entorhinal region and hippocampus have a critical role in supporting memory function (Abrahams et al, 1997;Scoville and Milner, 1957). While the magnitude of the effect we observed might be considered modest ($5%-20%), our finding that stimulation impaired memory might be unexpected in light of the report of Suthana et al (2012) showing 64% memory improvement from entorhinal stimulation.…”

“…Our results differ from both of these studies because we showed similar patterns of both spatial and verbal memory impairment irrespective of which hemisphere was stimulated. Because this effect persisted in a homogeneous population of patients who all had left-lateralized language function, it suggests that aspects of memory processing are supported in a holistic, network fashion (Kim et al, 2016). Further support for this network model of spatial cognition comes from our finding of a trend toward memory impairment from stimulation outside of the hippocampal formation (Figure 4).…”

Role of the hippocampus in memory functioning: modern view

“…Although besides the hippocampus functioning in the memory other brain regions take part also such as frontal and parietal regions [8], we still know little about their functional interaction with hippocampus during the memory formation and their role.…”

“…Other issues that remain involve whether DBS application should be provided unilaterally or bilaterally, and the characterization of the precise effects of DBS at anterior versus posterior hippocampus due to its diverse functional anatomy with heterogeneous neurons [23,7]. Kim, Ekstrom and Tandon have some interesting point of view (2016): they suggest approaches to reliably stimulation to enhance or disrupt memory; a network-level modulation of coherence is likely to be more effective than individual nodes stimulation (stimulating single hippocampus for example) in the memory network [8]. All of this suggests that DBS is a potentially useful method of influence on the hippocampus to improve memory, but it needs to be expanded and further researches must be held before DBS-based memory enhance methods can be introduced into clinical practice.…”