Auditory evoked brainstem and middle latency responses in Macaca mulatta and humans
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R E Lasky1, M M Maier, E B Snodgrass
1Neurology Department, University of Wisconsin-Madison Medical School 53792-5132, USA.
Abstract:
Early (ABRs) and middle (MLRs) surface-recorded auditory evoked potentials were compared in eight adult monkeys (Macaca mulatta) and eight adult humans. Responses whose probable generators were the cochlear nucleus and lateral lemniscus were of shorter latency and larger amplitude in monkeys. Relative to humans, ABR response latencies in monkeys were less affected by stimulus intensity, stimulus rate, and masker level. In contrast, monkey amplitudes were relatively more affected by those same stimulus parameters. The most prominent MLR wave was longer in latency and greater in amplitude in humans than the homologous wave in monkeys. The reduction in amplitude of that wave with increasing rate was greater for humans than monkeys. Temporal interactions (the effect of prior stimuli on the response to current stimulation) were investigated from a non-linear systems identification framework using maximum length sequences (MLSs). Both monkey and human auditory systems were second and probably third-order systems at the levels assessed. As the separations between the stimulus pulses decreased, evidence for temporal interactions became more prominent, reached a maximum, and then decreased with further decreases in stimulus pulse separation. At the highest stimulus rates presented, variations in temporal spacing among stimuli had less of an effect on monkey than human evoked responses.
Insights
Auditory evoked potentials in monkeys showed faster and larger responses than humans. Monkey auditory systems exhibited distinct temporal interaction patterns compared to humans, especially at high stimulus rates.
Area of Science:
- Neuroscience
- Auditory Neuroscience
- Comparative Physiology
Background:
- Auditory evoked potentials (AEPs), including early (ABRs) and middle (MLRs) components, are crucial for assessing auditory pathway function.
- Understanding species-specific differences in AEPs can elucidate fundamental principles of auditory processing.
- Previous research suggests variations in auditory system maturation and processing between primates and humans.
Purpose of the Study:
- To compare early (ABRs) and middle (MLRs) auditory evoked potentials between adult monkeys (Macaca mulatta) and adult humans.
- To investigate species-specific differences in response latency, amplitude, and parameter-dependent modulation.
- To characterize temporal interactions within the auditory system using non-linear systems identification.
Main Methods:
- Surface-recorded auditory evoked potentials (ABRs and MLRs) were measured in eight adult monkeys and eight adult humans.
- Stimulus parameters included intensity, rate, and masker level to assess response modulation.
- Non-linear systems identification using maximum length sequences (MLSs) was employed to study temporal interactions.
Main Results:
- Monkey ABRs (cochlear nucleus/lateral lemniscus) exhibited shorter latency and larger amplitude than humans.
- Monkey ABR latency was less affected by stimulus intensity, rate, and masker level, while amplitude was more affected.
- Human MLRs showed longer latency and greater amplitude, with a more pronounced amplitude reduction at higher rates compared to monkeys.
- Both species' auditory systems behaved as second and likely third-order systems.
- Temporal interactions became more prominent with decreased stimulus pulse separation, peaking and then declining.
- At high stimulus rates, monkey evoked responses were less affected by temporal spacing variations than human responses.
Conclusions:
- Significant species-specific differences exist in early and middle auditory evoked potentials between monkeys and humans.
- The auditory systems of both species demonstrate complex temporal interactions, with distinct patterns observed at high stimulus rates.
- These findings contribute to a comparative understanding of auditory processing mechanisms across primate species.
