title: Distinguishing cognitive state with multifractal complexity of hippocampal interspike interval sequences.
abstract: Fractality, represented as self-similar repeating patterns, is ubiquitous in nature and the brain. Dynamic patterns of hippocampal spike trains are known to exhibit multifractal properties during working memory processing; however, it is unclear whether the multifractal properties inherent to hippocampal spike trains reflect active cognitive processing. To examine this possibility, hippocampal neuronal ensembles were recorded from rats before, during and after a spatial working memory task following administration of tetrahydrocannabinol (THC), a memory-impairing component of cannabis. Multifractal detrended fluctuation analysis was performed on hippocampal interspike interval sequences to determine characteristics of monofractal long-range temporal correlations (LRTCs), quantified by the Hurst exponent, and the degree/magnitude of multifractal complexity, quantified by the width of the singularity spectrum. Our results demonstrate that multifractal firing patterns of hippocampal spike trains are a marker of functional memory processing, as they are more complex during the working memory task and significantly reduced following administration of memory impairing THC doses. Conversely, LRTCs are largest during resting state recordings, therefore reflecting different information compared to multifractality. In order to deepen conceptual understanding of multifractal complexity and LRTCs, these measures were compared to classical methods using hippocampal frequency content and firing variability measures. These results showed that LRTCs, multifractality, and theta rhythm represent independent processes, while delta rhythm correlated with multifractality. Taken together, these results provide a novel perspective on memory function by demonstrating that the multifractal nature of spike trains reflects hippocampal microcircuit activity that can be used to detect and quantify cognitive, physiological, and pathological states.
authors.affiliation: Neuroscience Program, Wake Forest School of Medicine Winston-Salem, NC, USA ; Department of Physiology and Pharmacology, Wake Forest School of Medicine Winston-Salem, NC, USA.
authors.forename: Dustin
authors.initials: D
authors.lastname: Fetterhoff
authors.affiliation: Department of Biomedical Engineering, Wake Forest School of Medicine Winston-Salem, NC, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Kraft
authors.affiliation: Department of Biomedical Engineering, University of Southern California Los Angeles, CA, USA.
authors.forename: Roman A
authors.initials: RA
authors.lastname: Sandler
authors.affiliation: Department of Physiology and Pharmacology, Wake Forest School of Medicine Winston-Salem, NC, USA.
authors.forename: Ioan
authors.initials: I
authors.lastname: Opris
authors.affiliation: Department of Biomedical Engineering, Wake Forest School of Medicine Winston-Salem, NC, USA.
authors.forename: Cheryl A
authors.initials: CA
authors.lastname: Sexton
authors.affiliation: Department of Biomedical Engineering, University of Southern California Los Angeles, CA, USA.
authors.forename: Vasilis Z
authors.initials: VZ
authors.lastname: Marmarelis
authors.affiliation: Department of Physiology and Pharmacology, Wake Forest School of Medicine Winston-Salem, NC, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Hampson
authors.affiliation: Department of Physiology and Pharmacology, Wake Forest School of Medicine Winston-Salem, NC, USA.
authors.forename: Sam A
authors.initials: SA
authors.lastname: Deadwyler
keywords: delayed nonmatch-to-sample; hippocampus; long-range temporal correlations; multifractal detrended fluctuation analysis; resting state; tetrahydrocannabinol (THC); working memory