An analysis of waves underlying grid cell firing in the medial enthorinal cortex

Layer II stellate cells in the medial enthorinal cortex (MEC) express hyperpolarisation-activated cyclic-nucleotide-gated (HCN) channels that allow for rebound spiking via an I_h current in response to hyperpolarising synaptic input. A computational modelling study by Hasselmo [2013 Neuronal rebound spiking, resonance frequency and theta cycle skipping may contribute to grid cell firing in medial entorhinal cortex. Phil. Trans. R. Soc. B 369: 20120523] showed that an inhibitory network of such cells can support periodic travelling waves with a period that is controlled by the dynamics of the I_h current. Hasselmo has suggested that these waves can underlie the generation of grid cells, and that the known difference in I_h resonance frequency along the dorsal to ventral axis can explain the observed size and spacing between grid cell firing fields. Here we develop a biophysical spiking model within a framework that allows for analytical tractability. We combine the simplicity of integrate-and-fire neurons with a piecewise linear caricature of the gating dynamics for HCN channels to develop a spiking neural field model of MEC. Using techniques primarily drawn from the field of nonsmooth dynamical systems we show how to construct periodic travelling waves, and in particular the dispersion curve that determines how wave speed varies as a function of period. This exhibits a wide range of long wavelength solutions, reinforcing the idea that rebound spiking is a candidate mechanism for generating grid cell firing patterns. Importantly we develop a wave stability analysis to show how the maximum allowed period is controlled by the dynamical properties of the I_h current. Our theoretical work is validated by numerical simulations of the spiking model in both one and two dimensions

Spontaneous Reorientation Is Guided by Perceived Surface Distance, Not by Image Matching Or Comparison

Humans and animals recover their sense of position and orientation using properties of the surface layout, but the processes underlying this ability are disputed. Although behavioral and neurophysiological experiments on animals long have suggested that reorientation depends on representations of surface distance, recent experiments on young children join experimental studies and computational models of animal navigation to suggest that reorientation depends either on processing of any continuous perceptual variables or on matching of 2D, depthless images of the landscape. We tested the surface distance hypothesis against these alternatives through studies of children, using environments whose 3D shape and 2D image properties were arranged to enhance or cancel impressions of depth. In the absence of training, children reoriented by subtle differences in perceived surface distance under conditions that challenge current models of 2D-image matching or comparison processes. We provide evidence that children’s spontaneous navigation depends on representations of 3D layout geometry.National Institutes of Health (U.S.) (Grant HD 23103

Spatial Learning and Action Planning in a Prefrontal Cortical Network Model

The interplay between hippocampus and prefrontal cortex (PFC) is fundamental to spatial cognition. Complementing hippocampal place coding, prefrontal representations provide more abstract and hierarchically organized memories suitable for decision making. We model a prefrontal network mediating distributed information processing for spatial learning and action planning. Specific connectivity and synaptic adaptation principles shape the recurrent dynamics of the network arranged in cortical minicolumns. We show how the PFC columnar organization is suitable for learning sparse topological-metrical representations from redundant hippocampal inputs. The recurrent nature of the network supports multilevel spatial processing, allowing structural features of the environment to be encoded. An activation diffusion mechanism spreads the neural activity through the column population leading to trajectory planning. The model provides a functional framework for interpreting the activity of PFC neurons recorded during navigation tasks. We illustrate the link from single unit activity to behavioral responses. The results suggest plausible neural mechanisms subserving the cognitive “insight” capability originally attributed to rodents by Tolman & Honzik. Our time course analysis of neural responses shows how the interaction between hippocampus and PFC can yield the encoding of manifold information pertinent to spatial planning, including prospective coding and distance-to-goal correlates

Cultivating safeness from the inside out: understanding the processes and developing a compassion-based intervention for psychosis

Tese de Doutoramento em Psicologia, na especialidade de Psicologia Clínica, apresentada à Faculdade de Psicologia e de Ciências da Educação da Universidade de CoimbraGiven the challenging and often distressing characteristics of experiences occurring before, during and after a psychotic episode, emotional dysfunction after psychosis is a widely common reality. Although overlooked for a long time, psychological interventions have important benefits in coping with psychotic symptoms or loss of functions, reducing the burden of the disease and enhancing patients’ lives. From the recovery model’s perspective, psychological interventions should promote richer and more positive self-experiences across several dimensions, thus shifting from a symptom-focused approach to a more person-based approach. This paradigm shift entails clinical and research implications regarding assessment, research on psychological mechanisms and intervention methods and outcomes. Contextual behavioural approaches, emphasizing the importance of mechanisms such as compassion, mindfulness and acceptance, have the potential to be key interventions for people with psychosis. Thus, this projects’ aims were: 1) to contribute to the development and validation of adequate assessment tools, through a) the development and validation of a clinical interview for psychotic disorders based on the recovery model and b) the development and/or validation of self-report measures; 2) to extend the understanding on processes underlying the development and maintenance of psychotic symptoms and their impact; and 3) to develop, implement and evaluate a new compassion-based group intervention for people with psychosis. Methods: The present project comprises one descriptive study, two review studies and ten empirical studies. Empirical studies were conducted in adult, clinical samples of people with experience of psychosis. Methods to assess participants included self-report measures, clinician-reported measures (clinical interviews and rating scales) and instruments filled in by a significant-other of each participant. Three empirical studies were clinical, interventional studies and followed a longitudinal design, while the others assessed participants cross-sectionally (either for evaluating psychometric properties of instruments or associations between process and outcome variables). Results: Regarding the studies focused on assessment, overall our results highlight the adequate psychometric properties, clinical utility and pertinence of a new clinical interview and self-report measures designed to measure experiential acceptance towards delusions and voices, and to assess antipsychotic medication adherence. In what concerns processes underlying psychotic experiences and recovery, results highlighted the pervasive role of shame, self-criticism and fears of compassion in difficulties experienced by people with psychosis, on one hand, and the impact of mindfulness and positive affect on social safeness, on the other. Clinical studies further emphasized the safety, adequacy, acceptability and usefulness of compassion, acceptance and mindfulness-based interventions in this population. Furthermore, the COMPASS intervention showed benefits regarding self-to-self and self-to-others relationships, functioning and symptoms. Conclusions: Overall the studies presented in the research project emphasize the importance of social rank and contextual variables in the maintenance versus recovery from psychosis, from the assessment phase to the intervention planning and implementation. This entails important clinical and research implications, namely regarding the need to foster accepting and compassionate therapeutic environments rooted on care-giving social mentalities.Tendo em conta que as experiências que ocorrem antes, durante e após um episódio psicótico são desafiadoras e muitas vezes angustiantes, a disfunção emocional após a psicose é uma realidade amplamente comum. Embora negligenciadas durante muito tempo, as intervenções psicológicas têm benefícios importantes na capacidade de lidar com os sintomas psicóticos ou perda de funcionalidade, na redução da sobrecarga da doença e na melhoria da vida dos pacientes. Do ponto de vista do modelo recovery, as intervenções psicológicas devem promover experiências de autoconhecimento mais ricas e positivas em várias dimensões, havendo assim uma mudança de uma abordagem focada nos sintomas para uma abordagem mais baseada na pessoa. Esta mudança de paradigma tem importantes implicações clínicas e de investigação nos campos da avaliação psicológica, do estudo dos mecanismos psicológicos, e da intervenção. As abordagens comportamentais contextuais, enfatizando a importância de mecanismos como compaixão, atenção plena e aceitação, têm o potencial de serem intervenções-chave para pessoas com psicose. Assim, os objetivos deste projeto prenderam-se com: 1) contribuir para o desenvolvimento e validação de instrumentos de avaliação adequados, através a) do desenvolvimento e validação de uma entrevista clínica para perturbações psicóticas com base no modelo de recuperação, e b) do desenvolvimento e/ou validação de medidas de autorresposta; 2) ampliar a compreensão em relação aos processos subjacentes ao desenvolvimento e manutenção de sintomas psicóticos e seu impacto; e 3) desenvolver, implementar e avaliar uma nova intervenção em grupo baseada na compaixão para pessoas com psicose. Método: O presente projeto compreende um estudo descritivo, dois estudos de revisão e dez estudos empíricos. Os estudos empíricos foram realizados com amostras clínicas de adultos com experiência de psicose. Os métodos para avaliar os participantes incluíram medidas de autorrelato, medidas preenchidas pelo clínico (entrevistas clínicas e escalas de avaliação cotadas pelo clínico) e instrumentos preenchidos por uma pessoa significativa do participante. Três dos estudos empíricos foram estudos clínicos, intervencionais e seguiram um desenho longitudinal. Os restantes avaliaram transversalmente os participantes (seja para avaliar propriedades psicométricas de instrumentos ou para perceber as associações entre variáveis de processo e de resultado). Resultados: Em relação aos estudos focados na avaliação, os nossos resultados destacam as propriedades psicométricas adequadas, utilidade clínica e pertinência de uma nova entrevista clínica e de medidas de autorrelato desenhadas para medir a aceitação experiencial em relação a delírios e vozes, e para avaliar a adesão à medicação anti-psicótica. No que diz respeito aos estudos que exploraram os processos subjacentes às experiências psicóticas e à recuperação, os resultados destacaram o papel nefasto da vergonha, autocrítica e medos de compaixão nas dificuldades experimentadas pelas pessoas com psicose, por um lado, e o impacto da atenção plena e do afeto positivo no sentimento de segurança em contextos sociais, por outro. Os estudos clínicos enfatizaram a segurança, adequação, aceitabilidade e utilidade das intervenções baseadas na compaixão, aceitação e atenção plena nesta população. Além disso, a intervenção COMPASS mostrou benefícios no que concerne as relações dos participantes consigo próprios e com os outros, o seu funcionamento e sintomas. Conclusões: De maneira geral, os estudos apresentados neste projeto enfatizam a importância de variáveis contextuais na manutenção versus recuperação da psicose, desde a fase da avaliação ao planeamento e implementação da intervenção. Isto acarreta importantes implicações clínicas e de investigação, nomeadamente no que diz respeito à necessidade de promover ambientes terapêuticos de aceitação e compaixão baseados na mentalidade social de prestação de cuidados