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BME 6938 Neurodynamics Instructor: Dr Sachin S Talathi Phase of limit cycle Isochrons-Define phase off limit cycle Phase of a non periodic point is taken to be the phase of its periodic proxy Phase Response Curve Weak Coupling- Infinitesimal PRC Linear Response Function or iPRC Practical Approach to Calculating iPRC Malkin’s Theorem: Let the system have exponentially stable limit cycle with period T and receive infinitesimal periodic perturbation Then its phase is described by equation Where with (XPPAUTO exploits this theorem to estimate iPRC) Brain rhythms (EEG) correlate with behavioral states •Delta (0.5-4 Hz): Dominant rhythm in infants and stage 3 and 4 of sleep Excited •Theta (4-8 Hz): Normal activity in young children and represents drowsiness in adults •Alpha (8-12 Hz): It is observed in relaxed state Relaxed •Beta (12-30 Hz): Observed in an anxious state Drowsy •Gamma (>30 Hz): Observed in attention state and is thought to be the learning rhythm Deep Sleep Neural synchrony: Mechanism for generation of brain rhythms Synchronous activity is large-detectable at the electrodes on the scalp (source of EEG) Neural Synchrony and the Binding Problem No central location in the brain where all information related to a task is centralized How are the parallel computations in spatially segregated regions in the brain coordinated? How are signals selected and routed from sensory structures to executive structures without confounding? How information about relatedness of content is encoded? Related to the problem of consciousness Potential Answer: Neural synchrony How does synchrony arise? Two key mechanisms. Related to the intrinsic properties of neurons in terms their preference for input frequencies (resonance) Related to the pattern of connectivity between neurons and the dynamic properties of intervening synapses (network and network interactions) Note: These are not mutually exclusive explanations Weakly coupled oscillators Substitute Note where Two weakly coupled oscillators represents deviation from the identical period for each oscillator Analyze Simple network-Weak Coupled Oscillators d A A H dt d B B dt d H dt Phase Locked Solution: H * dH Stability Criteria: 0 d * Results from Weak Coupling Theory Analysis Spike Time Response Curves perturbation time Coupling parameters T j T0 j t,T0 , E I ,gs, R , D T0 Intrinsic period Analysis of the network using STRCs n 1 n TB TA 1 1 n 2 n Phase Locked Solution: 1 1 Stability Criterion: 0 * 2 * d x 2 dx x * x x x 1 2 TB TA Results from analysis using STRCs