What type of responses are recorded over the primary somatosensory cortex to median somatosensory evoked potentials (SSEPs)?

The primary somatosensory cortex is responsible for processing sensory information from the body, specifically tactile stimuli. When examining median somatosensory evoked potentials (SSEPs), the interaction between these potentials and the cortex can vary based on the location of the recorded responses.

Negative nearfield responses are specifically associated with the primary somatosensory cortex because they reflect the direct cortical activation due to sensory input. These responses appear as negative peaks within the short latency range following the stimulus, signifying a direct response from the cortex rather than from more distant neural structures.

In this context, the nearfield responses specifically record the activity from neurons that are closer to the electrode, which is why they are classified as "nearfield." These negative peaks indicate a rapid and direct processing of the sensory input.

Farfield responses, on the other hand, tend to capture the effects of more distal brain structures and are often characterized by different polarities. Recognizing the distinction between nearfield and farfield responses is crucial for accurate interpretations in clinical practices involving SSEPs. Negative nearfield responses are a key indicator of cortical function and neural conduction in response to stimuli, making this the correct choice.