Audiology: Auditory Late Latency Potential

Auditory Late Latency Potential

• Late latency potentials (>80ms) in AEPs are cortical in origin, and are larger and lower in frequency than early and middle-latency potentials.
• They are highly dependent on stimulus type, recording location, recording technique, patient age, and state.

The Auditory P1-N1-P2 Complex

• Discovered in 1939 by P.A.Davis, who described changes in EEG in response to sound.
• Not specific to the auditory modality, as similar responses with different cortical sources are seen with visual or somatosensory stimulation.
• Provides information regarding the arrival of sound information to the auditory cortex.

Components of Late Latency Responses

• Four components:
  • P1: occurs between 55 and 80 ms
  • N1: occurs between 90 and 110 ms
  • P2: occurs between 145 and 180 ms
  • N2: occurs between 180 and 250 ms

P1 Component

• First vertex positive peak of the P1-N1-P2 complex
• Typically occurs approximately 50 msec after stimulus onset in adults with normal hearing
• Thought to represent late thalamic projections into the early auditory cortex and is part of the specific sensory system
• Strongly related to stimulus parameters
• Generators:
  • Primary auditory cortex (Heschl’s gyrus)
  • Hippocampus
  • Planum temporale
  • Lateral temporal regions
  • Possibly subcortical regions

N1 Component

• Prominent negative deflection in the auditory event-related potential (ERP)
• Primarily an exogenous potential, occurring at about 100 ms after the onset of an auditory stimulus
• Associated with the activity of the non-specific polysensory system within the contralateral supratemporal auditory cortex
• Often described as an “onset” response, signaling the neural encoding of sound onset at the level of the auditory cortex
• Generators:
  • Multiple generators in the primary and secondary auditory cortex include 3 underlying components:
    • Frontocentral negativity: N1b of first component N1