Synaptic Noise - Physiological Relevance

Physiological Relevance

Synaptic noise has been associated with high frequency oscillations (HFOs) within the brain. HFOs are imperative to normal brain function, and research has shown that synaptic noise may be a potential initiator of HFOs. HFOs between 60–70 Hz have been recorded as normal activity within the brain by EEG (electroencephalography) recordings, however frequencies within the ranges of 100–200 Hz, also called ripples, have been associated with epilepsy. Ripples, however, are not entirely abnormal nor regular. “Ripples have been used to describe both abnormal activity associated with epileptiform sharp waves and normal behaviors such as physiological sharp waves and memory consolidation.”

Synaptic noise is not only caused by mass signaling from surrounding neuronal impulses, but also from the direct signaling within the neuron itself. During episodes of epilepsy, the impulses fired are of greater magnitude and frequency than normal. Transient signaling, or more specifically noise, may shorten the resting potential in order to allow for quicker neural firing.

There is also evidence which supports the fact that epilepsy may be one cause of synaptic noise. During an epileptic seizure, tertiary bursts of action potential occur through the neurons in the brain. Neurons fire off randomly and rapidly creating the convulsive effect which the patient exhibits during the seizure. Before these bursts, there is an increase in the extracellular potassium concentrations of the neurons. "Potassium is expected to rise during epileptic discharges, and we have preliminary evidence from ventral slices exposed to bicuculline that potassium rises to a threshold value of ~9 mM just prior to the onset of tertiary bursts." The increased potassium concentrations outside the neuron can increase terminal excitability, causing possible action potential firing, which leads to synaptic noise.