Evolutionary Elongation of the Time Window of Integration in Auditory Cortex: Macaque vs. Human Comparison of the Effects of Sound Duration on Auditory Evoked Potentials

Abstract Background: Transcranial magnetic stimulation (TMS)-evoked potentials (TEPs), recorded using electroencephalography (EEG), reflect a combination of TMS-induced cortical activity and multi-sensory responses to TMS. The auditory evoked potential (AEP) is a high-amplitude sensory potential—evoked by the “click” sound produced by every TMS pulse—that can dominate the TEP and obscure observation of other neural components. The AEP is peripherally evoked and therefore should not be stimulation site specificObjectives/Methods: We address the problem of disentangling the peripherally evoked AEP of the TEP from components evoked by cortical stimulation and ask whether removal of AEP enables more accurate isolation of TEP. We hypothesized that isolation of the AEP using Independent Components Analysis (ICA) would reveal features that are stimulation site specific and unique individual features. In order to improve the effectiveness of ICA for removal of AEP from the TEP, and thus more clearly separate the transcranial-evoked and non-specific TMS-modulated potentials, we merged sham and active TMS datasets representing multiple stimulation conditions, removed the resulting AEP component, and evaluated performance across different sham protocols and clinical populations using reduction in Global and Local Mean Field Potentials (GMFA/LMFA) and cosine similarity analysis.Results: We show that removing AEPs significantly reduced GMFA and LMFA in the post-stimulation TEP (14 to 400 ms), driven by time windows consistent with the N100 and P200 temporal characteristics of AEPs. Cosine similarity analysis supports that removing AEPs reduces TEP similarity between subjects and reduces TEP similarity between stimulation conditions. Similarity is reduced most in a mid-latency window consistent with the N100 time-course, but nevertheless remains high in this time window. Residual TEP in this window has a time-course and topography unique from AEPs, which follow-up analyses suggest could be a modulation in the alpha band that is not stimulation site specific but is unique to individual subject.Conclusion(s): We show, using two datasets and two implementations of sham, evidence in cortical topography, TEP time-course, GMFA/LMFA and cosine similarity analyses that this procedure is effective and conservative in removing the AEP from TEP, and thereby reveals better defined TMS-evoked activity. We show TEP remaining in early, mid and late latencies. The early response is site and subject specific. Later responses are consistent with TMS-modulated alpha activity that is not site specific but is unique to the individual. TEP remaining after removal of AEP is unique and can provide insight into TMS-evoked potentials and other modulated oscillatory dynamics.

Download Full-text

Competition for neuronal resources: how hallucinations make themselves heard

The British Journal of Psychiatry ◽

10.1192/bjp.bp.106.022954 ◽

2007 ◽

Vol 190 (1) ◽

pp. 57-62 ◽

Cited By ~ 70

Author(s):

Daniela Hubl ◽

Thomas Koenig ◽

Werner K. Strik ◽

Lester Melie Garcia ◽

Thomas Dierks

Keyword(s):

Auditory Cortex ◽

Evoked Potentials ◽

Auditory Evoked Potentials ◽

Primary Auditory Cortex ◽

Auditory Attention ◽

Auditory Hallucinations ◽

Auditory Stimuli ◽

Simultaneous Occurrence ◽

Auditory Verbal Hallucinations ◽

External Stimuli

BackgroundHallucinations are perceptions in the absence of a corresponding external sensory stimulus. However, during auditory verbal hallucinations, activation of the primary auditory cortex has been described.AimsThe objective of this study was to investigate whether this activation of the auditory cortex contributes essentially to the character of hallucinations and attributes them to alien sources, or whether the auditory activation is a sign of increased general auditory attention to external sounds.MethodThe responsiveness of the auditory cortex was investigated by auditory evoked potentials (N100) during the simultaneous occurrence of hallucinations and external stimuli. Evoked potentials were computed separately for periods with and without hallucinations; N100 power, topography and brain electrical sources were analysed.ResultsHallucinations lowered the N100 amplitudes and changed the topography, presumably due to a reduced left temporal responsivity.ConclusionsThis finding indicates competition between auditory stimuli and hallucinations for physiological resources in the primary auditory cortex. The abnormal activation of the primary auditory cortex may thus be a constituent of auditory hallucinations.

Download Full-text

Auditory evoked potentials from the primary auditory cortex of the cat: topographic and pharmacological studies

Electroencephalography and Clinical Neurophysiology/Evoked Potentials Section ◽

10.1016/0168-5597(90)90041-b ◽

1990 ◽

Vol 77 (3) ◽

pp. 225-232 ◽

Cited By ~ 17

Author(s):

Robert T. Knight ◽

Simon Brailowsky

Keyword(s):

Auditory Cortex ◽

Evoked Potentials ◽

Auditory Evoked Potentials ◽

Primary Auditory Cortex ◽

Pharmacological Studies

Download Full-text

Enhancement of Auditory-evoked Potentials in Musicians Reflects an Influence of Expertise but not Selective Attention

Journal of Cognitive Neuroscience ◽

10.1162/jocn.2008.20157 ◽

2008 ◽

Vol 20 (12) ◽

pp. 2238-2249 ◽

Cited By ~ 65

Author(s):

Simon Baumann ◽

Martin Meyer ◽

Lutz Jäncke

Keyword(s):

Selective Attention ◽

Auditory Cortex ◽

Evoked Potentials ◽

Time Course ◽

Auditory Evoked Potentials ◽

Sine Wave ◽

Event Related Potential ◽

Auditory Evoked Responses ◽

Density Mapping ◽

Sound Features

Instrumental tones and, in some instances, simple sine-wave tones were shown to evoke stronger auditory-evoked responses in musicians compared to nonmusicians. This effect was taken as an example for plasticity in the auditory cortex elicited by training. To date, however, it is unknown whether an enlarged cortical representation for (instrumental) tones or increased neuronal activity provoked by focused attention in musicians accounts for the reported difference. In an attempt to systematically investigate the influence of attention on the processing of simple sine wave and instrumental tones, we compared auditory-evoked potentials recorded from musicians and nonmusicians. During the electroencephalogram recording, the participants were involved in tasks requiring selective attention to specific sound features such as pitch or timbre. Our results demonstrate that the effect of selective attention on the auditory event-related potential (AEP) has a different time course and shows a different topography than the reproduced effect of music expertise at the N1 component or the previously demonstrated effect at the P2 component. N1 peak potentials were unaffected by attention modulation. These results indicate that the effect of music expertise, which was traced by current density mapping to the auditory cortex, is not primarily caused by selective attention, and it supports the view that increased AEPs on tones in musicians reflect an enlarged neuronal representation for specific sound features of these tones. However, independent from the N1–P2 complex, attention evoked an Nd-like negative component in musicians but not in nonmusicians, which suggests that plasticity also affects top–down processes.

Download Full-text