The amount of exposure determines generalization in animal perceptual learning using short inter-stimulus intervals

BackgroundA paradoxical enhancement of the magnitude of the N1 wave of the auditory event-related potential (ERP) has been described when auditory stimuli are presented at very short (<400 ms) inter-stimulus intervals (ISI). Here, we examined whether this enhancement is specific for the auditory system, or whether it also affects ERPs elicited by stimuli belonging to other sensory modalities.Methodology and Principal FindingsWe recorded ERPs elicited by auditory and somatosensory stimuli in 13 healthy subjects. For each sensory modality, 4800 stimuli were presented. Auditory stimuli consisted in brief tones presented binaurally, and somatosensory stimuli consisted in constant-current electrical pulses applied to the right median nerve. Stimuli were delivered continuously, and the ISI was varied randomly between 100 and 1000 ms. We found that the ISI had a similar effect on both auditory and somatosensory ERPs. In both sensory modalities, ISI had an opposite effect on the magnitude of the N1 and P2 waves: the magnitude of the auditory and the somatosensory N1 was significantly increased at ISI≤200 ms, while the magnitude of the auditory and the somatosensory P2 was significantly decreased at ISI≤200 ms.Conclusion and SignificanceThe observation that both the auditory and the somatosensory N1 are enhanced at short ISIs indicates that this phenomenon reflects a physiological property that is common across sensory systems, rather than, as previously suggested, unique for the auditory system. Two of the hypotheses most frequently put forward to explain this observation, namely (i) the decreased contribution of inhibitory postsynaptic potentials to the recorded scalp ERPs and (ii) the decreased contribution of ‘latent inhibition’, are discussed. Because neither of these two hypotheses can satisfactorily account for the concomitant reduction of the auditory and the somatosensory P2, we propose a third, novel hypothesis, consisting in the modulation of a single neural component contributing to both the N1 and the P2 waves.

Fast synaptic transmission requires a rapid clearance of the released neurotransmitter from the extracellular space. Glial glutamate transporters (excitatory amino acid transporters, EAATs) strongly contribute to glutamate removal. In this work, we investigated the paired-pulse plasticity of synaptically activated, glutamate transporter-mediated currents (STCs) in cortical layer 2/3 astrocytes. STCs were elicited by local electrical stimulation in layer 4 in the presence of ionotropic glutamate (AMPA and NMDA), GABAA, and GABAB receptor antagonists. In experiments with low [Na(+)]i (5 mM) intrapipette solution, STCs elicited by paired-pulse stimulation demonstrated paired-pulse facilitation (PPF) at short (<250 ms) interstimulus intervals (ISIs) and paired-pulse depression at longer ISIs. In experiments with close to physiological, high [Na(+)]i (20 mM) intrapipette solution, PPF of STCs at short ISIs was significantly reduced. In addition, the STC kinetics was slowed in the presence of high [Na(+)]i. Exogenous GABA increased astrocytic [Na(+)]i, reduced the mean STC amplitude, decreased PPF at short ISIs, and slowed STC kinetics. All GABA-induced changes were blocked by NO-711 and SNAP-5114, GABA transporter (GATs) antagonists. In experiments with the low intrapipette solution, GAT blockade under control conditions decreased PPF at short ISIs both at room and at near physiological temperatures. Dialysis of single astrocyte with low [Na(+)]i solution increased the amplitude and reduced PPR of evoked field potentials recorded in the vicinity of the astrocyte. We conclude that (1) endogenous GABA via GATs may influence EAAT functioning and (2) astrocytic [Na(+)]i modulates the short-term plasticity of STCs and in turn the efficacy of glutamate removal.

Processing homonymy and polysemy: Effects of sentential context and time-course following unilateral brain damage

The individual replicability of mismatch negativity at short and long inter-stimulus intervals

The auditory mismatch negativity (MMN) is an event-related potential (ERP) peaking about 100–250 ms after the onset of a deviant tone in a sequence of identical (standard) tones. Depending on the interstimulus interval (ISI) between standard and deviant tones, the MMN is suitable to investigate the pre-attentive auditory discrimination ability (short ISIs, ≤ 2 s) as well as the pre-attentive auditory memory trace (long ISIs, >2 s). However, current results regarding the MMN as an index for mild cognitive impairment (MCI) and dementia are mixed, especially after short ISIs: while the majority of studies report positive associations between the MMN and cognition, others fail to find such relationships. To elucidate these so far inconsistent results, we investigated the validity of the MMN as an index for cognitive impairment exploring the associations between different MMN indices and cognitive performance, more specifically with episodic memory performance which is among the most affected cognitive domains in the course of Alzheimer’s dementia (AD), at baseline and at a 5-year-follow-up. We assessed the amplitude of the MMN for short ISI (stimulus onset asynchrony, SOA = 0.05 s) and for long ISI (3 s) in a neuropsychologically well-characterized cohort of older adults at risk of dementia (subjective memory impairment, amnestic and non-amnestic MCI; n = 57). Furthermore, we created a novel difference score (ΔMMN), defined as the difference between MMNs to short and to long ISI, as a measure to assess the decay of the auditory memory trace, higher values indicating less decay. ΔMMN and MMN amplitude after long ISI, but not the MMN amplitude after short ISI, was associated with episodic memory at baseline (β = 0.38, p = 0.003; β = −0.27, p = 0.047, respectively). ΔMMN, but not the MMN for long ISIs, was positively associated with episodic memory performance at the 5-year-follow-up (β = 0.57, p = 0.013). The results suggest that the MMN after long ISI might be suitable as an indicator for the decline in episodic memory and indicate ΔMMN as a potential biomarker for memory impairment in older adults at risk of dementia.

The present study investigated how a dementing illness such as Alzheimer's disease, might affect an individual's recourse to higher order contextual information in the access and integration of lexical material in on-line discourse comprehension. More specifically, the experiment investigated the priming of homophones in a discourse context, by use of a cross-modal lexical decision task, and compared the performances of a group of six subjects with mild to moderate dementia of the Alzheimer's type (DAT) with those of a matched control group. The subjects listened to 2-sentence paragraphs and performed a lexical decision on visually presented targets that followed ambiguous prime words (or homophones) at two inter-stimulus intervals (ISIs): 330 and 1000 msec. When the target was a word, it was either an associate of the prime word, a probable inference suggested by the discourse, or an unrelated word. The control subjects primed both the discourse-appropriate and discourse-inappropriate associate of the homophone at short (330 msec) ISIs (but not an appropriate inference word), a finding which supports the exhaustive access model of ambiguity resolution. As the ISI was lengthened to 1000 msec, however, the discourse-appropriate inference word was primed, and reflects the operation of attention-dependent integrative strategies. The subjects with DAT primed both appropriate associates and inference words at the short ISI. At ISI of 1000 msec, the DAT subjects primed the appropriate associate and showed substantial inhibition priming of the inappropriate associate. These results point to disturbances in the selective automatic activation of lexical material, and in the conscious integration and elaboration of lexical material in ongoing discourse comprehension in persons with DAT.

Immunotoxic cholinergic lesions in the basal forebrain reverse the effects of entorhinal cortex lesions on conditioned odor aversion in the rat

The recording of brain event-related potentials (ERPs) is a widely used technique to investigate the neural basis of sensory perception and cognitive processing in humans. Due to the low magnitude of ERPs, averaging of several consecutive stimuli is typically employed to enhance the signal to noise ratio (SNR) before subsequent analysis. However, when the temporal interval between two consecutive stimuli is smaller than the latency of the main ERP peaks, i.e., when the stimuli are presented at a fast rate, overlaps between the corresponding ERPs may occur. These overlaps are usually dealt with by assuming that there is a simple additive superposition between the elicited ERPs and consequently performing algebraic waveform subtractions. Here, we test this assumption rigorously by providing a statistical framework that examines the presence of nonlinear additive effects between overlapping ERPs elicited by successive stimuli with short interstimulus intervals (ISIs). The results suggest that there are no nonlinear additive effects due to the time overlap per se but that, for the range of ISIs examined, the second ERP is modulated by the presence of the first stimulus irrespective of whether there is time overlap or not. In other words, two ERPs that overlap in time can still be written as an addition of two ERPs but with the second ERP being different from the first. This difference is also present in the case of nonoverlapping ERPs with short ISIs. The modulation effect elicited on the second ERP by the first stimulus is dependent on the ISI value.

The role of central auditory processing in reading skill development and reading disorders is unclear. The purpose of this study was to examine whether individuals with specific reading disabilities (SRD) have deficits in processing rapidly presented, serially ordered non-speech auditory signals. To this end, we compared 12 children with SRD and 12 children without SRD on their ability to detect differences and similarities in pure tones of 1000 and 2000 Hz when these signals were presented in pairs (same or different tones, randomly ordered) with short (50 ms) versus long (500 ms) inter-stimulus intervals (ISI). Results showed that the children with SRD had significant difficulty in discriminating between pure tones with short, but not long ISI, whereas the controls performed well with both short and long ISI. The two groups did not differ significantly on measures of attention (d2) and performance IQ, and there were no significant correlations between these measures and ISI performance. There were significant correlations between the short ISI performance and phonologic awareness test results when the two groups were combined. These findings support the specific rapid auditory processing deficit hypothesis of SRD. Examination of intra-subject variability in performance indicated that children from the SRD group showed both decrement in performance with time on task and high overall variability in performance as compared to the controls. These findings underpin the importance of using time-series analyses of performance.

Slow potential changes and choice reaction time as a function of interstimulus interval

The twitch force (Ft)-interval relation of cardiac muscle reflects recovery of calcium release from the sarcoplasmic reticulum (SR). The calcium content of the SR is thought to be reflected by force developed during a contracture (Fc), induced by rapid cooling to near 0 degrees C. In right ventricular trabeculae of rat, under control conditions, the Ft-interval relation consisted of recovery of Ft to steady state (early recovery), followed by a secondary increase of Ft up to a maximum at an interval of approximately 100 seconds (rest potentiation) and a decline of Ft at intervals greater than 100 seconds (rest depression). The mechanisms that may underlie recovery of force after the last twitch at short intervals are 1) time-dependent transport of Ca2+ from the uptake compartment of the SR to the release compartment, 2) recovery of slow inward Ca2+ current during the action potential, and 3) recovery of the Ca2+ release channels in the SR. The Fc-interval relation was similar to the Ft-interval relation in that both a rest potentiation and a rest depression phase were present. However, at short interstimulus intervals (less than 1 second), Fc was independent of time, suggesting that the mechanism underlying early recovery was bypassed. Ryanodine (0.1-10 nM) reduced rest potentiation in a dose-dependent manner and accelerated rest depression of both Ft and Fc. At high ryanodine concentration, a significant Fc could only be induced after short intervals. Significant acceleration of rest depression was observed at low ryanodine concentrations, when Ft at intervals of 5 seconds was kept constant by increasing the stimulus frequency of [Ca2+]o, suggesting that the ryanodine effect was enhanced by increased [Ca2+]i. Ryanodine also increased the rate of decay of postextrasystolic potentiation in a dose-dependent manner. A significant effect was observed in 10 nM ryanodine. The twitch was not prolonged by ryanodine at these concentrations. These results suggest that the small magnitude of the twitch at short intervals is due to the finite time required by SR Ca2+ release channels to fully recover after a twitch. Furthermore, the results offer support for the hypothesis that ryanodine (in the nanomolar range) promotes Ca2+ leak from the SR in a dose-dependent manner and thereby limits Ca2+ accumulation during the interstimulus interval. Therefore, it may be expected that the negative inotropic effect of ryanodine is due to the SR Ca2+ depletion, and it is not necessary to postulate that ryanodine "blocks" the Ca2+ release channels in the SR.

Event Abstract Back to Event Adaptation of the N170: Effects of stimulus category, presentation time and interstimulus interval Daniel C. Feuerriegel1*, Owen Churches2, Mark J. Kohler1 and Hannah A. Keage1 1 University of South Australia, School of Psychology, Social Work and Social Policy, Australia 2 Flinders University, School of Psychology, Australia Background Event-related potential neural adaptation studies of the N170 in face and object perception have been used to delineate the time course of neural processes in high-level vision. However, study designs have varied widely in regards to the duration of the adaptor stimulus and the interstimulus interval (ISI). If adaptor duration and ISI influence the extent of neural adaptation then these variables may explain discrepancies between past studies. We measured ERPs to faces and chairs (representing nonface objects) over different adaptor duration and ISI conditions to assess the independent and combined effects of these on the extent of neural adaptation. We also tested whether these adaptation effects were stimulus specific or reflected a general property of repeated high-level object processing. Methods A Double Pulse paradigm was used. In each an adaptor stimulus was followed by an interstimulus interval and then a test stimulus. Adaptor stimuli were presented for 200ms, 500ms or 1000ms and the ISI was set at 200ms or 500ms. Greyscale images of face and chair stimuli were presented at the adaptor and test level. Neural responses to stimuli were recorded using 64-channel EEG. N170 peak amplitude and peak latency measures were derived from responses to adaptor and test stimuli in each condition. Results Test stimulus evoked N170s were smaller (more positive) following longer adaptor stimulus durations and longer (500ms) ISIs. Face and chair test N170 amplitudes differed by adaptor duration only when adapted by the same stimulus, although this sensitivity was found in faces but not chairs when the ISI was 500ms. N170 peak latencies were slower with longer adaptor durations and shorter ISIs. N170 peak latency differences between test faces and chairs were only found with face adaptor stimuli, and only in 200ms ISI conditions and when the adaptor duration was 1000ms in the 500ms ISI condition. Discussion Findings indicate that N170 peak amplitude and peak latency are differently affected by adaptor duration and ISI. These results appear to be category selective; that is that face and chair adaptors have different adapting effects on face and chair test stimuli. Keywords: Neural adaptation, N170, face perception, repetition suppression, object perception, ERPs (Event-Related Potentials) Conference: ACNS-2013 Australasian Cognitive Neuroscience Society Conference, Clayton, Melbourne, Australia, 28 Nov - 1 Dec, 2013. Presentation Type: Poster Topic: Sensation and Perception Citation: Feuerriegel DC, Churches O, Kohler MJ and Keage HA (2013). Adaptation of the N170: Effects of stimulus category, presentation time and interstimulus interval. Conference Abstract: ACNS-2013 Australasian Cognitive Neuroscience Society Conference. doi: 10.3389/conf.fnhum.2013.212.00064 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 15 Oct 2013; Published Online: 25 Nov 2013. * Correspondence: Mr. Daniel C Feuerriegel, University of South Australia, School of Psychology, Social Work and Social Policy, Adelaide, South Australia, Australia, dfeuerriegel@unimelb.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Daniel C Feuerriegel Owen Churches Mark J Kohler Hannah A Keage Google Daniel C Feuerriegel Owen Churches Mark J Kohler Hannah A Keage Google Scholar Daniel C Feuerriegel Owen Churches Mark J Kohler Hannah A Keage PubMed Daniel C Feuerriegel Owen Churches Mark J Kohler Hannah A Keage Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Temporal Summation of Pain Evoked by Mechanical Stimulation in Deep and Superficial Tissue

The present study evaluated the use of slow rates of stimulus presentation on the accuracy of the N1-P2 cortical response in estimating hearing threshold. Long interstimulus intervals (ISI) allow the non-specific component of the N1 response to emerge, believed to reflect widespread cortical arousal that facilitates sensory and motor responses. We examined whether the non-specific N1 would be elicited at intensity levels near threshold. Event-related potentials were recorded to 0.5-, 1.0, and 4.0-kHz tone bursts with a long ISI (8–12 s) while the eleven subjects read a book. The stimulus level varied from -5 to 45 dB nHL. The 1.0-kHz tone burst was also presented with a shorter ISI (1.5–2.5 s), akin to that typically used in the audiological setting. The amplitude of N1-P2 was significantly enhanced in the long compared to short ISI condition, but, importantly, only for the stimuli with a level ≥25 dB nHL. Therefore, the N1-P2 recorded with long ISIs was not more precise in estimating threshold than that recorded with short ISIs, remaining visible to within 10 dB of behavioural threshold.

The aim of this study was to determine whether there is a difference in the neural encoding of tones and complex sounds. Obligatory cortical auditory evoked potentials were obtained from normal hearing adults using tones and complex sounds with two stimulus durations and two inter-stimulus intervals. The response was smaller in amplitude for all of the long duration stimuli when using a short inter-stimulus interval. The difference in amplitude between the short and long duration tones disappeared when using the longer inter-stimulus interval but persisted for the complex sounds. The results provide evidence for duration-sensitive neurons in the auditory cortex as well as evidence for differences in the neural encoding of tones and complex sounds.