general principles part 1 historical and classifications

Henry P. Trahan, Au.D.

AUD 744AUD 744Overview of Overview of

Auditory Evoked ResponsesAuditory Evoked ResponsesTransitional Audiology ProgramTransitional Audiology Program

AUD 616 AUD 616 Auditory Evoked ResponsesAuditory Evoked Responses

Residential Audiology ProgramResidential Audiology Program

Part 1 Part 1

Auditory Evoked Auditory Evoked ResponsesResponses

Historical OverviewHistorical Overview

And And

General PrinciplesGeneral Principles

1929 – Human EEG -- Berger 1930 – First paper on AEPs in general --

Weaver and Bray 1930 – Earliest of AEPs discovered

– Cochlear Microphonic – Weaver and Bray

1939 – First recorded alteration in EEG with auditory stim. in humans – P. Davis

1941 – CM recorded from round window in human through TM perforation – Pearlman and Case

Historical Time LineHistorical Time Line

Henry P. Trahan, Au.D.

1950 – Summating Potential in animal recorded – Davis

1958 – Description of average response computer (ARC) – Clark

1967 – AP with earlobe electrodes. ABR response first shown but

reported as ECochG – Sohmer and Feinmesser

1971 – AP recorded in human w/external ear canal electrode – Saloman & Elberling

Historical Time LineHistorical Time Line

Henry P. Trahan, Au.D.

1971 – ABR first described in animals - Jewett

1971 – ABR response first described in humans – Jewett, Romano, Williston

1974 – CM, SP, and AP record in human w/ ear canal electrode -- Coats

1974 – Relationship between ECochG abnormalities and Meniere’s disease – Eggermont

1974 – Description of ABR in infants & young children – Hecox and Galambos

Historical Time LineHistorical Time Line

Henry P. Trahan, Au.D.

Electrical potentials in the human nervous system can be recorded both in response to specific external stimuli (event-related potentials [ERP] ) and in an ongoing manner without the presence of external stimuli (non-evoked or non-event related).

Evoked Versus Evoked Versus

Non-EvokedNon-Evoked ResponsesResponses

Henry P. Trahan, Au.D.

Non-Event Related Event Related

EEG ECochG

ABR

Evoked Versus Evoked Versus Non-Evoked ResponsesNon-Evoked Responses

Henry P. Trahan, Au.D.

Auditory Evoked Responses (AERs) represent electrical responses of the Auditory nervous system to externally presented acoustic stimuli.

Henry P. Trahan, Au.D.

Auditory Evoked Auditory Evoked ResponsesResponses

1. AEPs can be classified according to whether their characteristics are determined by external or internal processes (exogenous vs. endogenous)

2. AEPs can be classified according to the time epoch following the stimulus in which they occur. (latency)

3. AEPs can be classified according to the relation of the recording electrodes to the actual generator sites. (Near Field vs. Far Field)

4. AEPs can be classified according to what structures in the auditory system generates them.

Henry P. Trahan, Au.D.

Classification of Auditory Evoked ResponsesClassification of Auditory Evoked Responses

Henry P. Trahan, Au.D.

Classification of Auditory Evoked ResponsesClassification of Auditory Evoked Responses

1. AEPs can be classified according to whether their characteristics are determined by external or internal processes.

Exogenous Endogenous

Jeffrey L. Alexander, Ph.D.

Classification of AEPsClassification of AEPs2. AEPs can be classified according

to the time epoch following the stimulus in which they occur.

– Very Early (0 – 1.5 msec) (First) (CM, SP, N1) (ECochG)

– Early (1.5 -12 msec) (Fast) Nerve and brainstem) (ABR)

– Middle (12 - 50 msec) (thalamus and aud. cortex) (MLR)

– Slow (50 – 300 msec) (1o and 2o areas of cortex) (ALR)

– P300 (300+ msec) (1o and association areas) (P300)

Jeffrey L. Alexander, Ph.D.

The Family of AEPsThe Family of AEPs

Jeffrey L. Alexander, Ph.D.

The Family of AEPsThe Family of AEPs

vertex positive

III

IIIIV V

VI

No

Po

Na

Pa

Nb

P1

N1

P2

N2

P300

Jeffrey L. Alexander, Ph.D.

Classification of AEPsClassification of AEPs

3. AEPs can be classified according to the relation of the recording electrodes to the actual generator sites.

– Far-Field Response (Electrodes some distance away)

– Near-Field Response (Electrodes in close proximity)

Jeffrey L. Alexander, Ph.D.

Clinically, AEPs are almost always recorded at far-field., with electrodes located outside of the skull (extracranially), usually at the scalp. Two exceptions are:

1. During intraoperative monitoring (when recording electrodes mat be placed directly on the VIIIth Nerve) and

2. During transtympanic membrane ECochG, (when a recording electrode may be placed on the promontory).

Jeffrey L. Alexander, Ph.D.

4. AEPs can be classified according to what structures in the auditory system generates them.

– Receptor Potentials (cochlear hair cells)

– Neurogenic Potentials (VIIIth N &/or brain stem)

Classification of AEPsClassification of AEPs