What is the expected cortical response time when stimulating the median nerve at the wrist in a normal adult?

When stimulating the median nerve at the wrist in a normal adult, the expected cortical response time is about 20 milliseconds. This timing reflects the latency involved in neural conduction from the site of stimulation through the peripheral nerves to the spinal cord, and then up to the primary sensory cortex in the brain.

The latency can vary based on several factors, including the individual’s age and health, but standard values in clinical neurophysiology typically range from 18 to 22 milliseconds for this type of stimulation under normal conditions.

In this context, selecting around 20 milliseconds aligns with established reference values in neurophysiology literature, which indicate the time it takes for sensory signals conveyed through the median nerve to elicit a cortical response. Other responses, such as the visible twitch in specific muscles, relate to motor responses rather than sensory processing times, further clarifying why the focus is on the expected latency to the cortex in this scenario.