Detecting time lag between a pair of time series using visibility graph algorithm.

Estimating the time lag between a pair of time series is of significance in many practical applications. In this article, we introduce a method to quantify such lags by adapting the visibility graph algorithm, which converts time series into a mathematical graph. Currently widely used method to detect such lags is based on cross-correlations, which has certain limitations.

Estimation of Dynamic Bivariate Correlation Using a Weighted Graph Algorithm.

Dynamic correlation is the correlation between two time series across time. Two approaches that currently exist in neuroscience literature for dynamic correlation estimation are the sliding window method and dynamic conditional correlation. In this paper, we first show the limitations of these two methods especially in the presence of extreme values.

The Hippocampus and Dorsolateral Striatum Integrate Distinct Types of Memories through Time and Space, Respectively.

Several decades of research have established that different kinds of memories result from the activity of discrete neural networks. Studying how these networks process information in experiments that target specific types of mnemonic representations has provided deep insights into memory architecture and its neural underpinnings. However, in natural settings reality confronts organisms with problems that are not neatly compartmentalized.

Correction to: graph analysis of structural brain networks in Alzheimer's disease: beyond small world properties.

The original version of the article contained an error in the electronic supplementary material. The caption of the figure in the electronic supplementary material was omitted.

Place cell firing cannot support navigation without intact septal circuits.

Though it has been known for over half a century that interference with the normal activity of septohippocampal neurons can abolish hippocampal theta rhythmicity, a definitive answer to the question of its function has remained elusive. To clarify the role of septal circuits and theta in location-specific activity of place cells and spatial behavior, three drugs were delivered to the medial septum of rats: Tetracaine, a local anesthetic; muscimol, a GABA-A agonist; and gabazine, a GABA-A antagonist. All three drugs disrupted normal oscillatory activity in the hippocampus.

Graph analysis of structural brain networks in Alzheimer's disease: beyond small world properties.

Changes in brain connectivity in patients with early Alzheimer's disease (AD) have been investigated using graph analysis. However, these studies were based on small data sets, explored a limited range of network parameters, and did not focus on more restricted sub-networks, where neurodegenerative processes may introduce more prominent alterations. In this study, we constructed structural brain networks out of 87 regions using data from 135 healthy elders and 100 early AD patients selected from the Open Access Series of Imaging Studies (OASIS) database.

Contributions of Hippocampus and Striatum to Memory-Guided Behavior Depend on Past Experience.

Unlabelled: The hippocampal and striatal memory systems are thought to operate independently and in parallel in supporting cognitive memory and habits, respectively. Much of the evidence for this principle comes from double dissociation data, in which damage to brain structure A causes deficits in Task 1 but not Task 2, whereas damage to structure B produces the reverse pattern of effects. Typically, animals are explicitly trained in one task.

Applications of temporal kernel canonical correlation analysis in adherence studies.

Adherence to medication is often measured as a continuous outcome but analyzed as a dichotomous outcome due to lack of appropriate tools. In this paper, we illustrate the use of the temporal kernel canonical correlation analysis (tkCCA) as a method to analyze adherence measurements and symptom levels on a continuous scale. The tkCCA is a novel method developed for studying the relationship between neural signals and hemodynamic response detected by functional MRI during spontaneous activity.

Relative contributions of CA3 and medial entorhinal cortex to memory in rats.

The hippocampal CA1 field processes spatial information, but the relative importance of intra- vs. extra-hippocampal sources of input into CA1 for spatial behavior is unclear. To characterize the relative roles of these two sources of input, originating in the hippocampal field CA3 and in the medial entorhinal cortex (MEC), we studied effects of discrete neurotoxic lesions of CA3 or MEC on concurrent spatial and nonspatial navigation tasks, and on synaptic transmission in afferents to CA1.

Memory modulates journey-dependent coding in the rat hippocampus.

Neurons in the rat hippocampus signal current location by firing in restricted areas called place fields. During goal-directed tasks in mazes, place fields can also encode past and future positions through journey-dependent activity, which could guide hippocampus-dependent behavior and underlie other temporally extended memories, such as autobiographical recollections. The relevance of journey-dependent activity for hippocampal-dependent memory, however, is not well understood.

Representing episodes in the mammalian brain.

Memory lets the past inform the present so that we can attain future goals. In many species, these abilities require the hippocampus. Recent experiments, in which memory demand was varied while overt behavior and the environment were kept constant, have revealed firing patterns of hippocampal neurons that corresponded with memory demands and predicted performance.

Episodic memory--from brain to mind.

Neuronal mechanisms of episodic memory, the conscious recollection of autobiographical events, are largely unknown because electrophysiological studies in humans are conducted only in exceptional circumstances. Unit recording studies in animals are thus crucial for understanding the neurophysiological substrate that enables people to remember their individual past. Two features of episodic memory--autonoetic consciousness, the self-aware ability to "travel through time", and one-trial learning, the acquisition of information in one occurrence of the event--raise important questions about the validity of animal models and the ability of unit recording studies to capture essential aspects of memory for episodes.

Relative spike timing in pairs of hippocampal neurons distinguishes the beginning and end of journeys.

Episodic memory organizes experience in time, so that we can review past events and anticipate the future. In a hippocampus-dependent memory task, spike timing in pairs of simultaneously active CA1 neurons with overlapping place fields distinguished the start and end of trials. At the common starting point of different journeys, the relative spike timing of the neurons was highly correlated.

Prospective and retrospective memory coding in the hippocampus.

The effect of memory on hippocampal neuronal activity was assessed as rats performed a spatial task that was impaired by fornix lesions. The influences of current location, recently entered places, and places about to be entered were compared. Three new findings emerged.

Both dorsal and ventral hippocampus contribute to spatial learning in Long-Evans rats.

The hippocampus (HPC) may be functionally heterogeneous in supporting spatial learning in rats. Thus, dorsal but not ventral HPC lesions have been reported to impair acquisition in the Morris water task which consists of finding a submerged platform in a pool filled with opaque water. To further investigate the functional differences between dorsal and ventral HPC regions, we used a one-trial matching to position water task in which the submerged platform occupied a different position during each session.