Improved functional connectivity network estimation for brain networks using multivariate partial coherence.

Objective: Graphical networks and network metrics are widely used to understand and characterise brain networks and brain function. These methods can be applied to a range of electrophysiological data including electroencephalography, local field potential and single unit recordings. Functional networks are often constructed using pair-wise correlation between variables.

Adaptive spectral tracking for coherence estimation: the z-tracker.

Objective: A major challenge in non-stationary signal analysis is reliable estimation of correlation. Neurophysiological recordings can be many minutes in duration with data that exhibits correlation which changes over different time scales. Local smoothing can be used to estimate time-dependency, however, an effective framework needs to adjust levels of smoothing in response to changes in correlation.

Methylmercury bioaccumulation in an urban estuary: Delaware River USA.

Spatial variation in mercury (Hg) and methylmercury (MeHg) bioaccumulation in urban coastal watersheds reflects complex interactions between Hg sources, land use, and environmental gradients. We examined MeHg concentrations in fauna from the Delaware River estuary, and related these measurements to environmental parameters and human impacts on the waterway. The sampling sites followed a north to south gradient of increasing salinity, decreasing urban influence, and increasing marsh cover.

Hippocampal Neural Disinhibition Causes Attentional and Memory Deficits.

Subconvulsive hippocampal neural disinhibition, that is reduced GABAergic inhibition, has been implicated in neuropsychiatric disorders characterized by attentional and memory deficits, including schizophrenia and age-related cognitive decline. Considering that neural disinhibition may disrupt both intra-hippocampal processing and processing in hippocampal projection sites, we hypothesized that hippocampal disinhibition disrupts hippocampus-dependent memory performance and, based on strong hippocampo-prefrontal connectivity, also prefrontal-dependent attention. In support of this hypothesis, we report that acute hippocampal disinhibition by microinfusion of the GABA-A receptor antagonist picrotoxin in rats impaired hippocampus-dependent everyday-type rapid place learning performance on the watermaze delayed-matching-to-place test and prefrontal-dependent attentional performance on the 5-choice-serial-reaction-time test, which does not normally require the hippocampus.

Sex differences in learned fear expression and extinction involve altered gamma oscillations in medial prefrontal cortex.

Sex differences in learned fear expression and extinction involve the medial prefrontal cortex (mPFC). We recently demonstrated that enhanced learned fear expression during auditory fear extinction and its recall is linked to persistent theta activation in the prelimbic (PL) but not infralimbic (IL) cortex of female rats. Emerging evidence indicates that gamma oscillations in mPFC are also implicated in the expression and extinction of learned fear.

Non-parametric directionality analysis - Extension for removal of a single common predictor and application to time series.

Background: The ability to infer network structure from multivariate neuronal signals is central to computational neuroscience. Directed network analyses typically use parametric approaches based on auto-regressive (AR) models, where networks are constructed from estimates of AR model parameters. However, the validity of using low order AR models for neurophysiological signals has been questioned.

Too little and too much: hypoactivation and disinhibition of medial prefrontal cortex cause attentional deficits.

Attentional deficits are core symptoms of schizophrenia, contributing strongly to disability. Prefrontal dysfunction has emerged as a candidate mechanism, with clinical evidence for prefrontal hypoactivation and disinhibition (reduced GABAergic inhibition), possibly reflecting different patient subpopulations. Here, we tested in rats whether imbalanced prefrontal neural activity impairs attention.

Persistent prelimbic cortex activity contributes to enhanced learned fear expression in females.

Anxiety disorders, such as post-traumatic stress, are more prevalent in women and are characterized by impaired inhibition of learned fear and medial prefrontal cortex (mPFC) dysfunction. Here we examined sex differences in fear extinction and mPFC activity in rats. Females showed more learned fear expression during extinction and its recall, but not fear conditioning.

Assessing cortico-hippocampal functional connectivity under anesthesia and kainic acid using generalized partial directed coherence.

A significant challenge in modern neuroscience lies in determining the functional connectivity between discrete populations of neurones and brain regions. In this study, a variation of partial directed coherence, the generalized partial directed coherence (gPDC), along with a newly proposed critical value for gPDC, were applied on recorded local field potentials (LFPs) and single-unit activity, in order to assess information flow between medial prefrontal cortex (mPFC) and hippocampus and within the hippocampus of the rat brain, under isoflurane anesthesia and kainic acid-induced enhanced neuronal activity. Our findings suggest that, under anesthesia, there exists a continuous information flow from hippocampus towards mPFC, reversed mostly during activity bursts occurring in the mPFC.

Early life programming of fear conditioning and extinction in adult male rats.

The early rearing environment programs corticolimbic function and neuroendocrine stress reactivity in adulthood. Although early environmental programming of innate fear has been previously examined, its impact on fear learning and memory later in life remains poorly understood. Here we examined the role of the early rearing environment in programming fear conditioning and extinction in adult male rats.

Cannabinoid receptor activation reverses kainate-induced synchronized population burst firing in rat hippocampus.

Cannabinoids have been shown to possess anticonvulsant properties in whole animal models of epilepsy. The present investigation sought to examine the effects of cannabinoid receptor activation on kainic acid (KA)-induced epileptiform neuronal excitability. Under urethane anesthesia, acute KA treatment (10 mg kg(-1), i.

Ultrasonic vocalisations explain unexpected effects on pre-pulse inhibition responses in rats chronically pre-treated with phencyclidine.

Deficits in pre-pulse inhibition (PPI-indicative of psychosis in humans) can be replicated in rats using the NMDA receptor antagonist phencyclidine (PCP). Ultrasonic vocalisations (USVs) produced by rats in response to acoustic startle are indicative of heightened anxiety; here we tested the predictive validity of USVs as an indicator of PPI. Male juvenile Sprague-Dawley rats (n=10) were treated for 14 days with either PCP (5mg/kg i.

Neonatal maternal separation alters reward-related ultrasonic vocalizations in rat dams.

We examined the effects of brief or long durations of repeated maternal separation (MS) on ultrasonic vocalizations (USVs) in rat dams. 50-kHz USVs putatively identified as maternal in origin were emitted only immediately after pups were returned following MS. Maternal USV emission also depended on separation duration and pup age.

Early life programming of innate fear and fear learning in adult female rats.

The early rearing environment can impact on emotional reactivity and learning later in life. In this study the effects of neonatal maternal separation (MS) on innate fear and fear learning were assessed in the adult female rat. Pups were subjected to MS (360 min), brief handling (H; 15 min), or animal facility rearing (AFR) on post-natal days 2-14.

Early life stress causes FG-7142-induced corticolimbic dysfunction in adulthood.

Maternal separation (MS) during the neonatal period enhances stress responsivity in adulthood. The medial prefrontal cortex (mPFC) and the basolateral amygdala (BLA) are involved in coordinating various stress responses. Evidence indicates that MS reduces benzodiazepine and GABA(A) receptor expression in these regions, although their effects on neuronal function in the mPFC and the BLA remain unknown.

Systemic administration of the benzodiazepine receptor partial inverse agonist FG-7142 disrupts corticolimbic network interactions.

The medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) coordinate various stress responses. Although the effects of stressors on mPFC and BLA activity have been previously examined, it remains unclear to what extent stressors affect functional interactions between these regions. In vivo electrophysiology in the anesthetized rat was used to examine mPFC and BLA activity simultaneously in response to FG-7142, a benzodiazepine receptor partial inverse agonist that mimics various stress responses, in an attempt to model the effects of stressors on corticolimbic functional connectivity.