3 research outputs found
Assessing Neuronal Synchrony and Brain Function Through Local Field Potential and Spike Analysis
Studies of neuronal network oscillations and rhythmic neuronal synchronization have led to a number of important insights in recent years, giving us a better understanding of the temporal organization of neuronal activity related to essential brain functions like sensory processing and cognition. Important principles and theories have emerged from these findings, including the communication through coherence hypothesis, which proposes that synchronous oscillations render neuronal communication effective, selective, and precise. The implications of such a theory may be universal for brain function, as the determinants of neuronal communication inextricably shape the neuronal representation of information in the brain. However, the study of communication through coherence is still relatively young. Since its articulation in 2005, the theory has predominantly been applied to assess cortical function and its communication with downstream targets in different sensory and behavioral conditions. The results herein are intended to bolster this hypothesis and explore new ways in which oscillations coordinate neuronal communication in distributed regions. This includes the development of new analytic tools for interpreting electrophysiological patterns, inspired by phase synchronization and spike train analysis. These tools aim to offer fast results with clear statistical and physiological interpretation
Mean field modelling of human EEG: application to epilepsy
Aggregated electrical activity from brain regions recorded via an electroencephalogram (EEG),
reveal that the brain is never at rest, producing a spectrum of ongoing oscillations that
change as a result of different behavioural states and neurological conditions. In particular,
this thesis focusses on pathological oscillations associated with absence seizures that typically
affect 2–16 year old children. Investigation of the cellular and network mechanisms for absence
seizures studies have implicated an abnormality in the cortical and thalamic activity in the
generation of absence seizures, which have provided much insight to the potential cause of this
disease. A number of competing hypotheses have been suggested, however the precise cause
has yet to be determined. This work attempts to provide an explanation of these abnormal
rhythms by considering a physiologically based, macroscopic continuum mean-field model of
the brain's electrical activity. The methodology taken in this thesis is to assume that many
of the physiological details of the involved brain structures can be aggregated into continuum
state variables and parameters. The methodology has the advantage to indirectly encapsulate
into state variables and parameters, many known physiological mechanisms underlying the
genesis of epilepsy, which permits a reduction of the complexity of the problem. That is, a
macroscopic description of the involved brain structures involved in epilepsy is taken and then
by scanning the parameters of the model, identification of state changes in the system are
made possible. Thus, this work demonstrates how changes in brain state as determined in
EEG can be understood via dynamical state changes in the model providing an explanation
of absence seizures. Furthermore, key observations from both the model and EEG data
motivates a number of model reductions. These reductions provide approximate solutions of
seizure oscillations and a better understanding of periodic oscillations arising from the involved
brain regions. Local analysis of oscillations are performed by employing dynamical systems
theory which provide necessary and sufficient conditions for their appearance. Finally local
and global stability is then proved for the reduced model, for a reduced region in the parameter
space. The results obtained in this thesis can be extended and suggestions are provided for
future progress in this area
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Freeman's mass action
Freeman's Mass Action (FMA) refers to the collective synaptic actions that neurons in the cortex exert on each other in vast numbers by synchronizing their firing of action potentials. In the aggregate, FMA is a powerful force that creates bursts of cortical neural activity that resemble the vortices of tornadoes and hurricanes. The bursts rapidly and repeatedly retrieve memories and bind them with sensory information into percepts. In this way, FMA expresses and transmits the meaning of sensory information in spatial patterns of cortical activity that resemble frames in a movie