Multiple Areas Discrete Sources

Macroscopic electrophysiological techniques can resolve the course of neural population activation with sub-millisecond temporal resolution. This is adequate to detect the synchronous volley of action potentials that can result from electrical stimulation or sharp physiological activation and allows the characterization of oscillatory activity that can emerge within a network or by interactions between brain regions. In practice, most responses measured noninvasively do not disclose significant structure at time scales below a few milliseconds. A few specialized methods such as auditory brain stem evoked responses or electrical stimulation of the median nerve elicit a tightly correlated volley of action potentials that can be measured externally. However, most NEM evoked responses are a few milliseconds to tens of milliseconds wide and occur tens of milliseconds to hundreds of milliseconds after a stimulus event.

Dynamic responses of neural tissue involve a number of distinct processes. In response to upstream neural activity (or by endogenous processes in certain specialized sensor neurons, such as retinal photore-ceptors or hair cells of the auditory system), the neuron generates an electrical response. This response is typically initiated by the flow of ionic currents though transmembrane protein channels in the plasma membranes of the neuronal dendritic tree. These currents produce a change in the standing potential across the membrane and produce potential gradients along the neuron. These potential gradients give rise to passive currents that flow along dendritic processes to rapidly equilibrate the membrane potential. Most neurons contain other channel proteins whose properties are voltage-sensitive; an excursion of the membrane potential from its typical resting value across some threshold produces a conformational change that opens an ion-specific conductance. This transient conductance change gives rise to an action potential or spike. Subsequent responses by other voltage-sensitive channels within the neuronal membrane shut down the action potential and allow recovery of the membrane potential to resting levels.

Breaking Bulimia

Breaking Bulimia

We have all been there: turning to the refrigerator if feeling lonely or bored or indulging in seconds or thirds if strained. But if you suffer from bulimia, the from time to time urge to overeat is more like an obsession.

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