P50

P50, P-50, or P.50 may refer to:

P50 (neuroscience)

In electroencephalography, the P50 is an event related potential occurring approximately 50 ms after the presentation of a stimulus, usually an auditory click. The P50 response is used to measure sensory gating, or the reduced neurophysiological response to redundant stimuli.

Research has found an abnormal P50 suppression in people with schizophrenia, making it an example of a biological marker for the disorder. Besides schizophrenia, abnormal P50 suppression has been found in patients with traumatic brain injury, recreational drug use, and post-traumatic stress disorder.

Paired click test

In a paired click test, one auditory click sound will be presented, followed by a second click approximately 200 ms after the first one. The second sound is considered redundant, and so a typical control showing normal sensory gating will produce a reduced response (in wave amplitude) to the second click. The suppression is measured as the percentage of amplitude decrease in response to the second click compared to the first click, with typical controls showing an approximately 80% decrease to the second stimulus. This response is recorded at the scalp and represents a pre-attentive process of sensory gating.

P50 (pressure)

In biochemistry, P₅₀ indicates the partial pressure of a gas required to achieve 50% enzyme saturation. Values of P₅₀ are negatively correlated with substrate affinity, with lower values of P₅₀ corresponding to high affinity and vice versa. The term is analogous to the Michaelis-Menten constant (K_m), which identifies the concentration of substrate required for an enzyme to achieve 50% of its maximum reaction velocity.

For example, the P₅₀ of myoglobin for O₂ is 130 pascals while the P₅₀ for adult hemoglobin is 3.5 kPa. Thus, when O₂ partial pressure is low, hemoglobin-bound O₂ is more readily transferred to myoglobin. Myoglobin, found in high concentrations in muscle tissue, can then transfer the oxygen to muscle fibers, where it will be used in the generation of energy to fuel muscle contraction.

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