Synaptic Noise - in Sensory Neurons

In Sensory Neurons

Signals and noise in sensory receptors, which allow organisms to encode information based on their senses, set a limit on a given sensation. Oftentimes it is necessary to amplify a weak signal in order for it to be of use. For amplification to help, the signal at the synapse must be more intensified than the noise.

For example, amplification is needed when a single photon of light hits a rod photoreceptor in the retina of an eye. The amplification allows the small stimulus to overcome the noise that is an inherent characteristic of the cell. However, increasing the stimulus also increases the noise. This phenomenon has led to the question of how sensory receptors can lower synaptic noise effectively while amplifying the signal to reach threshold.

The sensitivity of a neuron increases when information from many receptors is collected and integrated - an event called pooling. While this allows a cell to focus predominantly on the actions that are directly involved with the stimulus, it also combines the noise, which increases the overall amount of noise present in the system.

A sensory neuron’s efficiency can be increased further if noise is eliminated as early as possible before pooling occurs, through linear filtering. The removal of noise in the beginning is crucial because once a signal and noise with similar timings combine, it is harder to separate them. Linear filtering involves the removal of noise with time frequencies that aren't associated with a given stimulus response. This removes events that are slower than the response, or not connected to the receptor in question.