296
W.E Dolphin
There have been a number of approaches to the classification and naming
of AEPs, however, a standardized nomenclature has yet to emerge (e.g.,
Ferraro and Durrant 1994). The classification and nomenclature of AEPs is
generally based on various aspects of the AEP itself or the stimulus evoking
the response. The most widely used classification of AEPs, largely adapted
from the work of Picton and Hillyand (1974), Picton and Hink (1974), and
Picton et al. (1977), is based on latency of response relative to stimulus
onset, and includes short latency responses (SLR: 0 to 20ms), middle
latency responses (MLR: 15 to 50ms), or long latency responses (LLR:
50 to 400ms); however, classifications based on anatomic origin (e.g.,
brain stem, cortical), stimulus-response relationship (e.g., transient versus
sustained, exogenous versus endogenous), and recording arrangements
(e.g., near-field versus far-field electrode placement) are also commonly
reported.
A standard and widely used measure of hearing in humans and other
animals involves a class of AEPs termed the auditory brain stem response
or ABR (sometime referred to in the audiology literature as the brain
stem auditory evoked response or BAER). ABRs are short latency (tens
of milliseconds) microvolt potentials evoked by acoustic stimuli. These
potentials are recorded in the far-field using computer averaging techniques
with electrodes located centimeters from the active tissue. The ABR is
a series of five to seven patterned and identifiable "waves," usually evoked
in response to clicks or short tone bursts that are manifested within the
first 20 ms after stimulus onset. ABRs were first reported in humans
by Sohmer and Feinmesser (1967) and later described in cats by Jewett
(1970). Subsequently, the various waves comprising the ABR were characterized and numerated in humans based on latency following delivery
of the stimulus (Jewett et al. 1970). The conventional method of identifying individual ABR peaks or waves is with roman numerals as per Jewett
et al. (1971).
Auditory brain stem responses reflect the synchronized, massed discharge
of large neuronal assemblies. As neural excitation moves through the auditory pathway, from the eighth nerve at least through the midbrain, the
resultant electrical potentials are measured from the scalp and appear as
sequential deflections in the ongoing EEG. However, the contribution of
specific cellular generators is still a matter of some debate (e.g., Mjjller
1994).
An example of an ABR from an adult Pseudorca crassidens, false killer
whale, obtained in response to a 50lls click presented at 120dB pe SPL
(peak equivalent, re IIlPa (i.e., 60 to 70dB > response threshold)) is shown
in Figure 7.1. As described above, the ABR is a series of five to seven waves,
usually occurring within 2ms of each other. Waves I, III, and V are generally considered to be the most clinically relevant components of the ABR.
The features of the response waveform most often used for clinical purposes have been indicated in Figure 7.1 and include the absolute latencies
W.E Dolphin
There have been a number of approaches to the classification and naming
of AEPs, however, a standardized nomenclature has yet to emerge (e.g.,
Ferraro and Durrant 1994). The classification and nomenclature of AEPs is
generally based on various aspects of the AEP itself or the stimulus evoking
the response. The most widely used classification of AEPs, largely adapted
from the work of Picton and Hillyand (1974), Picton and Hink (1974), and
Picton et al. (1977), is based on latency of response relative to stimulus
onset, and includes short latency responses (SLR: 0 to 20ms), middle
latency responses (MLR: 15 to 50ms), or long latency responses (LLR:
50 to 400ms); however, classifications based on anatomic origin (e.g.,
brain stem, cortical), stimulus-response relationship (e.g., transient versus
sustained, exogenous versus endogenous), and recording arrangements
(e.g., near-field versus far-field electrode placement) are also commonly
reported.
A standard and widely used measure of hearing in humans and other
animals involves a class of AEPs termed the auditory brain stem response
or ABR (sometime referred to in the audiology literature as the brain
stem auditory evoked response or BAER). ABRs are short latency (tens
of milliseconds) microvolt potentials evoked by acoustic stimuli. These
potentials are recorded in the far-field using computer averaging techniques
with electrodes located centimeters from the active tissue. The ABR is
a series of five to seven patterned and identifiable "waves," usually evoked
in response to clicks or short tone bursts that are manifested within the
first 20 ms after stimulus onset. ABRs were first reported in humans
by Sohmer and Feinmesser (1967) and later described in cats by Jewett
(1970). Subsequently, the various waves comprising the ABR were characterized and numerated in humans based on latency following delivery
of the stimulus (Jewett et al. 1970). The conventional method of identifying individual ABR peaks or waves is with roman numerals as per Jewett
et al. (1971).
Auditory brain stem responses reflect the synchronized, massed discharge
of large neuronal assemblies. As neural excitation moves through the auditory pathway, from the eighth nerve at least through the midbrain, the
resultant electrical potentials are measured from the scalp and appear as
sequential deflections in the ongoing EEG. However, the contribution of
specific cellular generators is still a matter of some debate (e.g., Mjjller
1994).
An example of an ABR from an adult Pseudorca crassidens, false killer
whale, obtained in response to a 50lls click presented at 120dB pe SPL
(peak equivalent, re IIlPa (i.e., 60 to 70dB > response threshold)) is shown
in Figure 7.1. As described above, the ABR is a series of five to seven waves,
usually occurring within 2ms of each other. Waves I, III, and V are generally considered to be the most clinically relevant components of the ABR.
The features of the response waveform most often used for clinical purposes have been indicated in Figure 7.1 and include the absolute latencies