Biology subjects

Morris, G.

Publications and source records attributed to Morris, G..

3 recordsLinked to original sources

bioRxiv2018

Early Life Trauma Predicts Affective Phenomenology and the Effects are Partly Mediated by Staging Coupled with Lowered Lipid-Associated Antioxidant Defences.

BackgroundEarly life trauma (ELT) may drive mood disorder phenomenology, neuro-oxidative and neuro-immune pathways and impairments in semantic memory. Nevertheless, there are no data regarding the impact of ELT on affective phenomenology and whether these pathways are mediated by staging or lowered lipid-associated antioxidant defences.\n\nMethodsThis study examined healthy controls (n=54) and patients with affective disorders including major depression, bipolar disorder and anxiety disorders (n=118). ELT was assessed using the Child Trauma Questionnaire. In addition, we measured affective phenomenology and assayed advanced oxidation protein products; malondialdehyde, paraoxonase 1 (CMPAase) activity, high-sensitivity C-reactive protein (hsCRP), and high-density lipoprotein (HDL) cholesterol.\n\nResultsELT was associated with increased risk for mood and comorbid anxiety disorders and a more severe phenomenology, including staging characteristics (number of mood episodes), severity of depression and anxiety, suicide attempts, suicidal ideation, type of treatments received, disabilities, body mass index, smoking behaviour and hsCRP, as well as lowered health-related quality of life, socio-economic status, antioxidant defences and semantic memory. The number of mood episodes and CMPAase/HDL-cholesterol levels could be reliably combined into a new vulnerability staging-biomarker index, which mediates in part the effects of ELT on affective phenomenology, while lowered antioxidant defences are associated with increased oxidative stress. Moreover, the effects of female sex on mood disorders and affective phenomenology are mediated by ELT.\n\nDiscussionThe cumulative effects of different types of ELT drive many aspects of affective phenomenology either directly or indirectly through effects of staging and/or lipid-associated antioxidant defences. The results show that children, especially girls, with ELT are at great risk to develop mood disorders and more severe phenotypes of affective disorders.

neuroscience↗

bioRxiv2018

Animal learning in amultidimensional discrimination task as explained by dimension-specific allocation of attention

Reinforcement learning describes the process by which during a series of trial-and-error attempts, actions that culminate in reward are strengthened. When the actions are based on sensory stimuli, an association is formed between the stimulus, the action and the reward. Computational, behavioral and neurobiological accounts of this process successfully explain simple stimulus-response learning. However, if the cue is multi-dimensional, identifying which of its features are relevant for the reward is not trivial, and the underlying cognitive process is poorly understood. To study this we adapted an intra-dimensional/ extra-dimensional set-shifting paradigm to train rodents on a multidimensional sensory discrimination task. In our setup, stimuli of different modalities (spatial, olfactory and visual) are combined into complex cues and manipulated independently. In each set, only a single stimulus dimension is relevant for reward. To distinguish between learning and decision-making we suggest a weighted attention model (WAM). It combines a learning model where each feature-dimension is reinforced separately with a decision rule that chooses an alternative according to a weighted average of learnt values, in which weight is associated with each dimension. We estimated the parameters of the WAM (decision weights, learning rate and noise) and demonstrated that is outperforms an alternative model in which a value learnt is assigned to each combination of features, or every state. Estimated decision weights of WAM reveal an experience-based bias in learning. The intra-dimensional set shift separated the decision weights. While in the first phase of the experiment the weights were roughly the same, in the second phase the weight on the dimension that was key to finding the reward became higher than others. After the extra-dimensional shift this dimension became irrelevant, however its decision weight remained high for the early learning stage in this last phase, providing an explanation for the poor performance of the animals. By the end of the phase when the rats performance improved, the weights for the two dimensions converged. Thus, estimated weights can be viewed as a possible way to quantify the experience-based bias.

animal behavior and cognition↗

bioRxiv2017

Odor concentration change detectors in the Olfactory Bulb

Dynamical changes in the environment strongly impact our perception 1,2. Consistent with this, sensory systems preferentially represent stimulus changes, enhancing temporal contrast 3,4. In olfaction, odor concentration changes across consecutive inhalations ({Delta}Ct) can guide odor source localization. Yet the neural representation of {Delta}Ct has not been studied in vertebrates. We have found that a subset of mitral/tufted (M/T) cells in the olfactory bulb explicitly represent {Delta}Ct. These concentration change detectors are direction selective: some respond to positive {Delta}Ct, while others represent negative {Delta}Ct. This change detection enhances the contrast between different concentrations and the magnitude of contrast enhancement scales with the size of the concentration step. Further, {Delta}Ct can be read out from the total spike count per sniff, unlike odor identity and intensity, which are represented by fast temporal spike patterns. Our results demonstrate that a subset of M/T cells explicitly represents {Delta}Ct, providing a signal that may instruct navigational decisions in downstream olfactory circuits.

neuroscience↗