Guide: Dr Laxmi T Rao, Associate Professor, Neurophysiology, NIMHANS
Examiner: Dr Kiranmai Rai S, Professor of Physiology at Kasturba Medical College International Center, Manipal
Neurophysiology @ NIMHANS |
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Saravanan S did the viva voce presentation for his PhD thesis entitled "Behavioural and electrophysiological assessment of neural dynamics in rat stroke model"
Guide: Dr Laxmi T Rao, Associate Professor, Neurophysiology, NIMHANS Examiner: Dr Kiranmai Rai S, Professor of Physiology at Kasturba Medical College International Center, Manipal Arun Sasidharan (PhD Scholar) presented the paper by Ford etal from the journal Schizophrenia Bulletin 2013 entitled "Did I Do That? Abnormal Predictive Processes in Schizophrenia When Button Pressing to Deliver a Tone "
ABSTRACT Motor actions are preceded by an efference copy of the motor command, resulting in a corollary discharge of the expected sensation in sensory cortex. These mechanisms allow animals to predict sensations, suppress responses to self-generated sensations, and thereby process sensations efficiently and economically. During talking, patients with schizophrenia show less evidence of pretalking activity and less suppression of the speech sound, consistent with dysfunction of efference copy and corollary discharge, respectively. We asked if patterns seen in talking would generalize to pressing a button to hear a tone, a paradigm translatable to less vocal animals. In 26 patients [23 schizophrenia, 3 schizoaffective (SZ)] and 22 healthy controls (HC), suppression of the N1 component of the auditory event–related potential was estimated by comparing N1 to tones delivered by button presses and N1 to those tones played back. The lateralized readiness potential (LRP) associated with the motor plan preceding presses to deliver tones was estimated by comparing right and left hemispheres’ neural activity. The relationship between N1 suppression and LRP amplitude was assessed. LRP preceding button presses to deliver tones was larger in HC than SZ, as was N1 suppression. LRP amplitude and N1 suppression were correlated in both groups, suggesting stronger efference copies are associated with stronger corollary discharges. SZ have reduced N1 suppression, reflecting corollary discharge action, and smaller LRPs preceding button presses to deliver tones, reflecting the efference copy of the motor plan. Effects seen during vocalization largely extend to other motor acts more translatable to lab animals. Kumari Anshu (PhD Scholar) presented the paper by Chang etal from Nature Neuroscience Feb 2013 entitled "Neuronal reference frames for social decisions in primate frontal cortex".
Abstract Social decisions are crucial for the success of individuals and the groups that they comprise. Group members respond vicariously to benefits obtained by others, and impairments in this capacity contribute to neuropsychiatric disorders such as autism and sociopathy. We examined the manner in which neurons in three frontal cortical areas encoded the outcomes of social decisions as monkeys performed a reward-allocation task. Neurons in the orbitofrontal cortex (OFC) predominantly encoded rewards that were delivered to oneself. Neurons in the anterior cingulate gyrus (ACCg) encoded reward allocations to the other monkey, to oneself or to both. Neurons in the anterior cingulate sulcus (ACCs) signaled reward allocations to the other monkey or to no one. In this network of received (OFC) and foregone (ACCs) reward signaling, ACCg emerged as an important nexus for the computation of shared experience and social reward. Individual and species-specific variations in social decision-making might result from the relative activation and influence of these areas. Ajay Nair (3rd year PhD Scholar) presented the paper by MM Arnold etal from Journal of Sleep Research, 2013 entitled "Information content in cortical spike trains during brain state transitions"
SUMMARY Even in the absence of external stimuli there is ongoing activity in the cerebral cortex as a result of recurrent connectivity. This paper attempts to characterize one aspect of this ongoing activity by examining how the information content carried by specific neurons varies as a function of brain state. We recorded from rats chronically implanted with tetrodes in the primary visual cortex during awake and sleep periods. Electroencephalogram and spike trains were recorded during 30-min periods, and 2–4 neuronal spikes were isolated per tetrode off-line. All the activity included in the analysis was spontaneous, being recorded from the visual cortex in the absence of visual stimuli. The brain state was determined through a combination of behavior evaluation, electroencephalogram and electromyogram analysis. Information in the spike trains was determined by using Lempel–Ziv Complexity. Complexity was used to estimate the entropy of neural discharges and thus the information content (Amigo´ et al. Neural Comput., 2004, 16: 717–736). The information content in spike trains (range 4–70 bits s)1) was evaluated during different brain states and particularly during the transition periods. Transitions toward states of deeper sleep coincided with a decrease of information, while transitions to the awake state resulted in an increase in information. Changes in both directions were of the same magnitude, about 30%. Information in spike trains showed a high temporal correlation between neurons, reinforcing the idea of the impact of the brain state in the information content of spike trains. Kumari Anshu Jha (2nd year PhD scholar) presented her seminar on "Interneuron dysfunction in neuropsychiatric disorders". She focused on GABAergic dysfunction in Schizophrenia and Autism.
Anshu gave an overview of Interneuron functions (feedback & feedforward inhibition, network oscillations and synchrony, modulation of excitability, integration and cortical development and plasticity) and then highlighted the complexity of internuron types (classified based on morphological, molecular, electrophysiological properties - eg Markram 2004). She then discussed the role of GABAergic neurons in the pathophysiology of Schizophrenia and then Autism from post-mortem studies and animal models (gene knockouts) while showing that GABA impairment seems to be present in a wide variety of neuropsychiatric disorders. She then went through the mechanisms through which these interneurons modulate network oscillations via electrical gap junctions and neurochemical modulations amongst the interneurons (for example Parvalbumin expressing basket cells impact gamma oscillations while somatostatin expressing interneurons impact beta oscillations). Considering that the type of impairment is similar for schizophrenia and autism, the timing of the impairment seems to be a differentiator between these two disorders. Autism is seen in early childhood (diagnosed around 3 years of age when neuronal pruning is still ongoing) and the first onset of Schizophrenia happens in adolescence (when the neurons are fully formed but the myelination is still an ongoing process). Maltesh K (1st year PhD Scholar) presented the paper by Warden et al from Nature 2012 entitled: "A prefrontal cortex–brainstem neuronal projection that controls response to behavioural challenge"
Abstract The prefrontal cortex (PFC) is thought to participate in high-level control of the generation of behaviours (including the decision to execute actions); indeed, imaging and lesion studies in human beings have revealed that PFC dysfunction can lead to either impulsive states with increased tendency to initiate action, or to amotivational states characterized by symptoms such as reduced activity, hopelessness and depressed mood. Considering the opposite valence of these two phenotypes as well as the broad complexity of other tasks attributed to PFC, we sought to elucidate the PFC circuitry that favours effortful behavioural responses to challenging situations. Here we develop and use a quantitative method for the continuous assessment and control of active response to a behavioural challenge, synchronized with single-unit electrophysiology and optogenetics in freely moving rats. In recording from the medial PFC (mPFC), we observed that many neurons were not simply movement-related in their spike-firing patterns but instead were selectively modulated from moment to moment, according to the animal’s decision to act in a challenging situation. Surprisingly, we next found that direct activation of principal neurons in the mPFC had no detectable causal effect on this behaviour. We tested whether this behaviour could be causally mediated by only a subclass of mPFC cells defined by specific downstream wiring. Indeed, by leveraging optogenetic projection-targeting to control cells with specific efferent wiring patterns, we found that selective activation of those mPFC cells projecting to the brainstem dorsal raphe nucleus (DRN), a serotonergic nucleus implicated in major depressive disorder, induced a profound, rapid and reversible effect on selection of the active behavioural state. These results may be of importance in understanding the neural circuitry underlying normal and pathological patterns of action selection and motivation in behaviour. |
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