Search

We experience the world through multiple senses simultaneously. To better understand mechanisms of multisensory processing we ask whether inputs from two senses (auditory and visual) can interact and drive plasticity in neural-circuits of the primary visual cortex (V1). Using genetically-encoded voltage and calcium indicators, we find coincident audio-visual experience modifies both the supra and subthreshold response properties of neurons in L2/3 of mouse V1. Specifically, we find that after audio-visual pairing, a subset of multimodal neurons develops enhanced auditory responses to the paired auditory stimulus. This cross-modal plasticity persists over days and is reflected in the strengthening of small functional networks of L2/3 neurons. We find V1 processes coincident auditory and visual events by strengthening functional associations between feature specific assemblies of multimodal neurons during bouts of sensory driven co-activity, leaving a trace of multisensory experience in the cortical network., Sensory stimuli usually arrive simultaneously but the neural-circuit mechanisms that combine multiple streams of sensory information are incompletely understood. The authors here show that visual-auditory pairing drives plasticity in multi-modal neuron networks within the mouse visual cortex.

The early stages of Alzheimer's disease (AD) have been linked to microcircuit dysfunction and pathophysiological neuronal firing in several brain regions. Inhibitory GABAergic microcircuitry is a critical feature of stable neural-circuit function in the healthy brain, and its dysregulation has therefore been proposed as contributing to AD-related pathophysiology. However, exactly how the critical balance between excitatory and inhibitory microcircuitry is modified by AD pathogenesis remains unclear. Here, we set the current evidence implicating dysfunctional GABAergic microcircuitry as a driver of early AD pathophysiology in a simple conceptual framework. Our framework is based on a generalised reductionist model of firing-rate control by local feedback inhibition. We use this framework to consider multiple loci that may be vulnerable to disruption by AD pathogenesis. We first start with evidence investigating how AD-related processes may impact the gross number of inhibitory neurons in the network. We then move to discuss how pathology may impact intrinsic cellular properties and firing thresholds of GABAergic neurons. Finally, we cover how AD-related pathogenesis may disrupt synaptic connectivity between excitatory and inhibitory neurons. We use the feedback inhibition framework to discuss and organise the available evidence from both preclinical rodent work and human studies in AD patients and conclude by identifying key questions and understudied areas for future investigation.

The adult neocortex is not hard-wired but instead retains the capacity to reorganise across multiple spatial scales long into adulthood. Plastic reorganisation occurs at the level of mesoscopic sensory maps, functional neuronal assemblies and synaptic ensembles and is thought to be a critical feature of neuronal network function. Here, we describe a series of approaches that use calcium imaging to measure network reorganisation across multiple spatial scales in vivo. At the mesoscopic level, we demonstrate that sensory activity can be measured in animals undergoing longitudinal behavioural assessment involving automated touchscreen tasks. At the cellular level, we show that network dynamics can be longitudinally measured at both stable and transient functional assemblies. At the level of single synapses, we show that functional subcellular calcium imaging approaches can be used to measure synaptic ensembles of dendritic spines in vivo. Finally, we demonstrate that all three levels of imaging can be spatially related to local pathology in a preclinical rodent model of amyloidosis. We propose that multi-scale in vivo calcium imaging can be used to measure parallel plasticity processes operating across multiple spatial scales in both the healthy brain and preclinical models of disease.

Negative and cognitive deficit symptoms in schizophrenia remain an unmet clinical need. Improved understanding of the neuro- and psychopathology of cognitive dysfunction in the illness is urgently required to enhance the development of new improved therapeutic strategies. Careful validation of animal models that mimic the behaviour and pathology of complex psychiatric disorders is an essential step towards this goal. Non-competitive NMDAR (N-Methyl-d-aspartate receptor) antagonists e.g. phencyclidine (PCP), ketamine and dizocilpine (MK-801) can effectively replicate certain aspects of negative and cognitive deficits associated with schizophrenia in animals. In 2010 we reviewed the effects of NMDAR antagonism in tests for domains of cognition affected in schizophrenia, social behaviour and neuropathology, and in 2014, in tests for negative symptoms. In this update, we evaluate the most recent pharmacological strategies for restoring cognition in schizophrenia using NMDAR antagonist models, published since our original review in 2010 (cited over 225 times, excluding self-citations). Tests reviewed are, novel object recognition for visual recognition memory, attentional set shifting for executive function, and operant tests incorporating recent touchscreen technology for a range of domains including working memory, problem solving and attention, all impaired in schizophrenia. Moreover, we include an update on parvalbumin (PV)-expressing GABAergic interneurons and review, for the first time, the effects of NMDAR antagonists on gamma oscillations, circuitry integral for effective cognition. Data summarized in this review strongly confirm the reliability and usefulness of NMDAR antagonist animal models for evaluating novel therapeutic candidates, and for improving our understanding of the pathophysiology of cognitive deficits in schizophrenia. This article is part of the Special Issue entitled 'Psychedelics: New Doors, Altered Perceptions'.

Background: Cognitive deficits and structural brain changes co-occur in patients with schizophrenia. Improving our understanding of the relationship between these is important to develop improved therapeutic strategies. Back-translation of these findings into rodent models for schizophrenia offers a potential means to achieve this goal. Aims: The purpose of this study was to determine the extent of structural brain changes and how these relate to cognitive behaviour in a sub-chronic phencyclidine rat model. Methods: Performance in the novel object recognition task was examined in female Lister Hooded rats at one and six weeks after sub-chronic phencyclidine (2 mg/kg intra-peritoneal, n=15) and saline controls (1 ml/kg intra-peritoneal, n=15). Locomotor activity following acute phencyclidine challenge was also measured. Brain volume changes were assessed in the same animals using ex vivo structural magnetic resonance imaging and computational neuroanatomical analysis at six weeks. Results: Female sub-chronic phencyclidine-treated Lister Hooded rats spent significantly less time exploring novel objects ( pConclusion: A sustained sub-chronic phencyclidine-induced cognitive deficit in novel object recognition is accompanied by global brain volume reductions in female Lister Hooded rats. The relative volumes of the perirhinal cortex however are positively correlated with novel object exploration, indicating some functional relevance.