Sensory neuroscience

Typical experiments

A typical experiment in sensory neuroscience involves the presentation of a series of relevant stimuli to an experimental subject while the subject's brain is being monitored. This monitoring can be accomplished by noninvasive means such as functional magnetic resonance imaging (fMRI) or electroencephalography (EEG), or by more invasive means such as electrophysiology, the use of electrodes to record the electrical activity of single neurons or groups of neurons. fMRI measures changes in blood flow which related to the level of neural activity and provides low spatial and temporal resolution, but does provide data from the whole brain. In contrast, Electrophysiology provides very high temporal resolution (the shapes of single spikes can be resolved) and data can be obtained from single cells. This is important since computations are performed within the dendrites of individual neurons.

Single neuron experiments

In most of the central nervous system, neurons communicate exclusively by sending each other action potentials, colloquially known as "spikes". It is therefore thought that all of the information a sensory neuron encodes about the outside world can be inferred by the pattern of its spikes. Current experimental techniques cannot measure individual spikes noninvasively. Such encoding includes the Dual Process Theory and how we think in a conscious and unconscious manner.

A typical single neuron experiment will consist of isolating a neuron (that is, navigating the neuron until the experimenter finds a neuron which spikes in response to the type of stimulus to be presented, and (optionally) determining that all of the spikes observed indeed come from a single neuron), then presenting a stimulus protocol. Because neural responses are inherently variable (that is, their spiking pattern may depend on more than just the stimulus which is presented, although not all of this variability may be true noise, since factors other than the presented stimulus may affect the sensory neuron under study), often the same stimulus protocol is repeated many times to get a feel for the variability a neuron may have. One common analysis technique is to study the neuron's average time-varying firing rate, called its post stimulus time histogram or PSTH.