Neural mechanisms of involuntary attention to acoustic novelty and change

Posttraining Sleep Enhances Automaticity in Perceptual Discrimination

Perceptual learning can develop over extended periods, with slow, at times sleep-dependent, improvement seen several days after training. As a result, performance can become more automatic, that is, less dependent on voluntary attention. This study investigates whether the brain correlates of this enhancement of automaticity are sleep-dependent. Event-related potentials produced in response to complex auditory stimuli were recorded while subjects' attention was focused elsewhere. We report here that following training on an auditory discrimination task, performance continued to improve, without significant further training, for 72 hr. At the same time, several event-related potential components became evident 48–72 hr after training. Posttraining sleep deprivation prevented neither the continued performance improvement nor the slow development of cortical dynamics related to an enhanced familiarity with the task. However, those brain responses associated with the automatic shift of attention to unexpected stimuli failed to develop. Thus, in this auditory learning paradigm, posttraining sleep appears to reduce the voluntary attentional effort required for successful perceptual discrimination by facilitating the intrusion of a potentially meaningful stimulus into one's focus of attention for further evaluation.

Event-related potentials associated with sound discrimination versus novelty detection in children

In children, deviant sounds in an oddball paradigm elicit a mismatch negativity (MMN) indexing discrimination of sound change and late difference negativity (LDN) with unknown functional significance. Salient sounds elicit an ERP index if orienting, P3a, and a late negative component, Nc. We compared children's responses elicited by moderate sound changes and novel sounds to examine the relationships between MMN and LDN, and LDN and Nc. Two components of the Nc, the Nc1 and Nc2, were identified. The scalp topography of LDN differed from those of the MMN and Nc1. Children's early P3a appeared mature but late P3a lacked frontal predominance. The findings suggested that LDN is not linked with either the sensory or attentional processing. It might reflect cognitive, albeit preattentive, processing of sound change. The Nc1 appears to reflect cognitive attentive processing of salient stimuli and the Nc2 might reflect reorienting after distraction.

Cross-form conceptual relations between sounds and words: effects on the novelty P3

In order for cross-form conceptual priming to occur, the brain must extract an amodal representation of the presented concept. To determine whether the novelty P3 would show such cross-form effects, novel, environmental sounds or their verbal equivalents were repeated two blocks after their first presentation in two cross-form conditions, word-sound (e.g., the word "pig" followed by the sound "oink") or sound-word. Conceptual repetition engendered an asymmetric reduction in novelty P3 amplitude, i.e., amplitude was reduced in the sound-word but not in the word-sound condition. The data suggest that the novelty P3 reflects an evaluative stage of processing in which some semantic information is extracted. However, the lack of amplitude reduction for the word-sound condition implies that, at least at the delays used here, repetition as a conceptually equivalent sound may have failed to make contact with the initial verbal concept.

Grammar Processing Outside the Focus of Attention: an MEG Study

To address the cerebral processing of grammar, we used whole-head high-density magnetoencephalography to record the brain's magnetic fields elicited by grammatically correct and incorrect auditory stimuli in the absence of directed attention to the stimulation. The stimuli were minimal short phrases of the Finnish language differing only in one single phoneme (word-final inflectional affix), which rendered them as either grammatical or ungrammatical. Acoustic and lexical differences were controlled for by using an orthogonal design in which the phoneme's effect on grammaticality was inverted. We found that occasional syntactically incorrect stimuli elicited larger mismatch negativity (MMN) responses than correct phrases. The MMN was earlier proposed as an index of preattentive automatic speech processing. Therefore, its modulation by grammaticality under nonattend conditions suggests that early syntax processing in the human brain may take place outside the focus of attention. Source analysis (single—dipole models and minimum-norm current estimates) indicated grammaticality dependent differential activation of the left superior temporal cortex suggesting that this brain structure may play an important role in such automatic grammar processing.

Test-retest reliability of auditory ERP components in healthy 6-year-old children

One prerequisite of using auditory event-related brain potentials (ERP) in developmental and clinical research is to determine their reliability. We examined the individual stability and test-retest reliability of the ERP responses elicited by repetitive, slightly deviant, and novel sounds over 3 months in healthy 6-year-old children. When broken down to 20 ms intervals, the standard-stimulus ERP responses shared > 77%, the deviant-stimulus responses 17-31%, and the novel-stimulus responses > 33% of the individual variation over the two testing sessions; the mean amplitude differences (novel/deviant-standard) did not change significantly between sessions. The sufficiently high individual stability of the ERP responses support the utility of these measurements for studying the effects of novel sounds in this age group.

Attention capture by auditory significant stimuli: semantic analysis follows attention switching

Event-related potentials (ERPs) were recorded from the scalp to investigate a long-standing controversy in auditory attention research, namely when the 'breakthrough of the unattended' takes place in the human brain. Nine subjects classified visual stimuli appearing 300 ms after task-irrelevant standard tones (80%, i.e. P = 0.8) or novel sounds (20%, i.e. P = 0.2) into odd/even categories. After the recording session, subjects scored the novel sounds as to whether they had any particular meaning (identifiable) or were perceived as a burst of noise (non-identifiable), and performance and ERPs were analysed according to this classification. A control condition, in which the visual stimuli were presented with no sounds, showed that subjects covertly monitored the task-irrelevant sounds during visual task-performance, and a further condition, in which the auditory and visual stimuli appeared regardless of each other, made it possible to trace the processing of the distracters during allocation of attention outside the auditory environment. Results yielded identical N1-enhancement for the two types of novel sounds, indicating similar attention switching triggered to these two types of unexpected sounds. However, there was a stronger orientating of attention towards identifiable novel sounds, as indicated both by behavioural distraction and by larger novelty-P3. Furthermore, this stronger orientating of attention was due to the sounds being contingent on the visual stimuli, as no increase in novelty-P3 to identifiable novel sounds was observed in the control condition, in which the sounds occurred outside the attentional set. Therefore, provided that the N1-enhancement reflects a call for focal attention, and novelty-P3 the effective orientating of attention towards the eliciting sounds, the present results suggest that semantic analysis of significant sounds occurs after a transitory switch of attention towards the eliciting stimuli. Moreover, as the novelty-P3 increase in amplitude was observed only when subjects covertly monitored the sounds, the present data suggest that semantic analysis of irrelevant sounds depends on the top-down cognitive influences of the attentional set.

Altered auditory processing in acutely psychotic never-medicated first-episode patients

Individuals with psychosis fail to differentiate external impulses and suffer from distortions of reality testing. Schizophrenia group illnesses are also associated with deficits in working memory and perception. We examined the manifestations of a very early phase of psychotic illness to automatic auditory deviance detection to clarify the basic mechanisms underlying misinterpretations of perception.

METHODS

Twenty-five never-medicated patients admitted for hospital evaluation of acute psychosis were studied. Fifty-eight EEG channels were recorded during an auditory oddball paradigm. Event-related potentials (ERPs) time-locked to non-attended deviant auditory stimuli were studied in patients and compared with healthy controls. Auditory processing was examined both at the level of the measured biosignals (standard and deviant responses) and with subtraction waveforms. Topographical differences were characterized using global field power (GFP) and minimum norm estimates.

RESULTS

The maximum GFP amplitudes and mean amplitudes of the 58 channels within the time windows corresponding to the previously known 'N2b', 'P3a' and 'P3b' components were clearly reduced in patients when compared to healthy controls. However, the groups did not differ during attention-independent automatic processing corresponding to the 'N1' and 'MMN' components, or with respect to the peak latencies of the GFP maxima.

CONCLUSIONS

Impairment of the processing of a deviance in simple auditory input in acutely ill drug-naive first-episode psychotic patients only appears in attention-dependent processing after about 250 ms. The alterations in auditory processing differed between stimulus types, suggesting at least two mechanisms underlying the auditory discrimination impairments in acute psychosis. After 250 ms there was a linear and gradually increasing difference in magnitude between the groups in their responses to deviant stimuli, probably related to arousal. In addition, however, there was a striking difference between the groups in the processing of standard stimuli. The early processing was similar in patients and controls, but the striking difference appeared in later processing. The sensory memory deficits associated with psychosis may be explained by an abnormality in sensory model formation rather than by impaired deviant detection.

Top-down control over involuntary attention switching in the auditory modality

We tested the effects of predictability on involuntary attention switching to task-irrelevant sound changes (distraction). Behavioral and neurophysiological evidence are provided, showing that the predictability of task-irrelevant sound changes eliminates effects of distraction even though the automatic auditory change detection system remains responsive. Two indices of distraction, slower task performance and cortical brain responses associated with attention switching, were seen only in the unpredictable condition, in which the irrelevant acoustic changes were unexpected. Attention was not involuntarily drawn away from the primary task when the subjects had foreknowledge of when the irrelevant changes would occur. These results demonstrate attentional control over orienting to sound changes and suggest that involuntary attention switching occurs mainly when an irrelevant stimulus change is unexpected. The present data allowed observation of the temporal dynamics of attention switching in the human brain.

The disruptive effect of chronic pain on mismatch negativity

OBJECTIVE

To investigate the effect of chronic pain on processes that generate the mismatch negativity (MMN).

METHODS

Twelve participants with a diagnosis of chronic intractable pain were tested before and after pain treatment. During testing, event-related potentials were recorded while participants performed tasks of varying difficulty.

RESULTS

The amplitude of the MMN was found to be greater following a nerve block procedure compared to MMN amplitude when participants were experiencing chronic pain. This effect was found to occur in the MMN for difficult-to-detect tones elicited while participants were performing a simultaneous cognitively demanding visual task. MMN amplitude was found to be greater with attention to difficult-to-detect deviants during pain but not in no pain conditions.

CONCLUSIONS

These results provide an electrophysiological correlate of previous findings that high levels of pain disrupt cognition during the performance of demanding tasks.

Nociceptive processing in the human brain of infrequent task-relevant and task-irrelevant noxious stimuli. A study with event-related potentials evoked by CO2 laser radiant heat stimuli

Laser evoked potentials (LEPs) are nociceptive-related brain responses to activation of cutaneous nociceptors by laser radiant heat stimuli. We previously showed that LEP amplitude during the P2 period (approximately 400 ms) was increased by rare noxious stimuli, inside and outside the focus of spatial attention. It was postulated that this effect reflected a P3a response indexing an involuntary shift of attention. In the present study, LEPs were recorded in a three-stimulus oddball paradigm, commonly used to evoke P3a (or novelty-P3). CO(2) laser-induced noxious stimuli were delivered on one hand (80%, frequent). Two series of rare stronger-intensity deviant stimuli were randomly intermixed: target stimuli (10%) were delivered on the same hand while distractor stimuli (10%) were delivered on the other hand. Subjects were instructed to count targets. During an additional session, strong stimuli were delivered alone on one hand without instruction (100%, no-task stimuli). All stimulus types evoked a first positivity around 360 ms (P360). Targets and distractors elicited a late positive complex (LPC) around 465-500 ms. Topography of LPC to distractors was central and significantly more anterior than that of LPC to targets. Distractor LPC corresponds to P3a (or novelty-P3) indexing an involuntary orientation of attention toward an unexpected new/deviant event. It suggests that at least an early part of the LEP positivity (P360) is independent of P3-activities.

Effects of sleep onset on the mismatch negativity (MMN) to frequency deviants using a rapid rate of presentation

This study examined the effects of sleep onset-the transition from a waking, conscious state to one of sleep and unconsciousness-on the mismatch negativity (MMN) following frequency deviants when a rapid rate of stimulus presentation is employed. The MMN is thought to reflect a brief-lasting sensory memory. Rapid rates of stimulus presentation should guard the sensory memory from fading. A 1,000 Hz standard stimulus was presented every 150 ms. At random, on 6.6% of the trials, the standard was changed to either a large 2,000 or a small 1,100 Hz deviant. During alert wakefulness (when subject ignored the stimuli and read a book), the large deviant elicited a larger deviant related negativity (DRN) than did the small deviant. This negativity may be a composite of both N1 and MMN activity while that following the small deviant is probably a 'true' MMN. The large deviant continued to elicit a DRN in relaxed wakefulness (eyes closed) and Stages 1 and 2 of sleep, although it was much reduced in amplitude. A significant MMN was recorded for the small deviant only in alert wakefulness. The failure to observe an MMN to small deviance and the attenuation of the DRN to large deviance at sleep onset therefore is probably not due to a decay of sensory memory. It is more likely that cortical encoding of both the standard and deviant is weakened during sleep onset because of prior thalamic inhibition of sensory input.

The electrophysiological net response ('F-complex') to spatial fusion of speech elements forming an auditory object

OBJECTIVE

The purpose of this study was to define and analyze the brain activity associated with fusion of speech elements to form an auditory object and to study the effects of presenting the elements at different spatial locations (duplex stimulus).

METHODS

Stimuli were formant transitions (presented to the front, left or right of the subject) and base (presented to the front), that fused to result in V-C-V sequences /aga/ and /ada/. Ten right-handed, adult, native Hebrew speakers discriminated each fused stimulus, and the brain potentials associated with performance of the task were recorded from 21 electrodes. The net-fusion response, the 'F(fusion)-complex', was extracted by subtracting the sum of potentials to the base and formant transitions from the potentials to the fused sound. Low resolution electromagnetic tomography analysis (LORETA) was performed to assess the timing and brain location of the fusion process.

RESULTS

The 'F-complex', comprising of the difference N(1), P(2), N(2b) (FN(1), FP(2), FN(2b)) components could be identified for each of the stimuli and reflected a process indicating inhibition, occlusion or both, with right ear advantage in fusion. LORETA analyses indicate sequential processing of speech fusion in the temporal lobes, beginning with right prominence in FN(1) and FP(2) shifting to a more symmetrical pattern in FN(2).

CONCLUSIONS

The electrophysiological correlates of speech fusion highlight the uniqueness of speech perception and the brain areas involved in its analysis.

Spatiotemporal dynamics of the auditory novelty-P3 event-related brain potential

The spatiotemporal dynamics of the cerebral network involved in novelty processing was studied by means of scalp current density (SCD) analysis of the novelty P3 (nP3) event-related brain potential (ERP). ERPs were recorded from 30 scalp electrodes at the occurrence of novel unpredictable environmental sounds during the performance of a visual discrimination task. Increased SCD was observed at left frontotemporal (FT3), bilateral temporoparietal (TP3 and TP4) and prefrontal locations (F8-F4 and F7-F3), suggesting novelty-P3 generators located in the left auditory cortex, and bilaterally in temporoparietal and prefrontal association regions. Additional increased SCD was found at a central location (Cz) and at superior parietal locations (P3-Pz-P4). The SCD of the nP3 was therefore generated at three successive, partially overlapping, stages of neuroelectric activation. At the central location, SCD started to be significant before the onset of the nP3 waveform, contributing solely to its early phase. At temporoparietal and left frontotemporal locations, nP3 electrophysiological activity was characterized by sustained current density, starting at about 210 ms and continuing during the full latency range of the response, including its early and late phases. At its late phase, the nP3 was characterized by sharp phasic current density at prefrontal and superior parietal locations, starting at about 290 ms and vanishing at around 385 ms. Taken together, these results provide the first evidence of the cerebral spatio-temporal dynamics underlying novelty processing.

Cortical operational synchrony during audio-visual speech integration

Information from different sensory modalities is processed in different cortical regions. However, our daily perception is based on the overall impression resulting from the integration of information from multiple sensory modalities. At present it is not known how the human brain integrates information from different modalities into a unified percept. Using a robust phenomenon known as the McGurk effect it was shown in the present study that audio-visual synthesis takes place within a distributed and dynamic cortical networks with emergent properties. Various cortical sites within these networks interact with each other by means of so-called operational synchrony (Kaplan, Fingelkurts, Fingelkurts, & Darkhovsky, 1997). The temporal synchronization of cortical operations processing unimodal stimuli at different cortical sites reveals the importance of the temporal features of auditory and visual stimuli for audio-visual speech integration.

Speech-sound-selective auditory impairment in children with autism: they can perceive but do not attend

In autism, severe abnormalities in social behavior coexist with aberrant attention and deficient language. In the attentional domain, attention to people and socially relevant stimuli is impaired the most. Because socially meaningful stimulus events are physically complex, a deficiency in sensory processing of complex stimuli has been suggested to contribute to aberrant attention and language in autism. This study used event-related brain potentials (ERP) to examine the sensory and early attentional processing of sounds of different complexity in high-functioning children with autism. Acoustically matched simple tones, complex tones, and vowels were presented in separate oddball sequences, in which a repetitive "standard" sound was occasionally replaced by an infrequent "deviant" sound differing from the standard in frequency (by 10%). In addition to sensory responses, deviant sounds elicited an ERP index of automatic sound-change discrimination, the mismatch negativity, and an ERP index of attentional orienting, the P3a. The sensory sound processing was intact in the high-functioning children with autism and was not affected by sound complexity or "speechness." In contrast, their involuntary orienting was affected by stimulus nature. It was normal to both simple- and complex-tone changes but was entirely abolished by vowel changes. These results demonstrate that, first, auditory orienting deficits in autism cannot be explained by sensory deficits and, second, that orienting deficit in autism might be speech-sound specific.

Effects of strain, novelty, and NMDA blockade on auditory-evoked potentials in mice

People with schizophrenia exhibit impaired ability to modify electroencephalographic event-related potential (ERP) responses to novel stimuli. These deficits serve as a window into the abnormalities of neuronal organization and function and are thought to reflect a component of genetic vulnerability for schizophrenia. We describe differences among inbred mouse strains for ERPs following a novelty detection paradigm, as a model for genetic contributions to disease vulnerability. Auditory-evoked potentials were recorded during an auditory oddball task in nonanesthetized C57BL/6J, C3H/HeJ, and DBA/2J mice prior to and following ketamine (10 mg/kg). Stimuli consisted of 80 sets of 24 standard tones followed by one novel tone. Principal component analysis yielded four temporal components that contribute to the auditory ERP responses to standard and novel stimuli. Two principal components that varied between standard and novel stimuli also differed among inbred mouse strains. Post hoc analyses indicate that strain effects on novelty detection are due to a significant difference between the response to novel and standard tones in C3H/HeJ mice that is absent in the other two strains. Inbred strains of mice vary in their ability to perform neuronal detection of change in the auditory environment. The ability to model novelty detection deficits in mice will aid in identifying genetic contributions to abnormal neuronal organization in people with schizophrenia.

Lorazepam induces an atypical dissociation of visual and auditory event-related potentials

Lorazepam has been reported to atypically disrupt visual processing compared to other benzodiazepines (BZs), but it is not known to what extent this effect extends to impairment in other modalities. Our objective was to compare the effects of lorazepam with those of flunitrazepam, a BZ with standard effects, on visual and auditory event-related potentials (ERPs) using the same paradigm. The study followed a placebo-controlled, double-blind, parallel group-design and involved single oral doses of lorazepam (2.0 mg), flunitrazepam (1.2 mg) and placebo. Thirty-six young, healthy subjects completed a test battery before and after treatment including classic behavioural tests, visual and auditory ERPs. Both drugs led to comparable alterations on behavioural tests and double-dissociations were found, indicating that the doses used were equipotent: lorazepam was more deleterious than flunitrazepam and placebo in fragmented shape identification, while simple reaction times were prolonged for flunitrazepam in comparison to lorazepam and placebo. Effects on P3 latencies were also distinct: alterations in both modalities for flunitrazepam were equivalent and greater than placebo's. In contrast, lorazepam at the frontal and central electrode sites led to greater changes in visual than in auditory latency, and also to longer visual latencies than flunitrazepam and placebo, but lorazepam's auditory latency effects were only different to placebo's at the parietal electrode site. Peripheral visual changes were not responsible for these effects. Differences in the impairment profile between equipotent doses of lorazepam and flunitrazepam suggests that lorazepam induces atypical central visual processing changes.

Neural sensitivity to human voices: ERP evidence of task and attentional influences

In an earlier study, we found that human voices evoked a positive event-related potential (ERP) peaking at approximately 320 ms after stimulus onset, distinctive from those elicited by instrumental tones. Here we show that though similar in latency to the Novelty P3, this Voice-Sensitive Response (VSR) differs in antecedent conditions and scalp distribution. Furthermore, when participants were not attending to stimuli, the response to voices was undistinguished from other harmonic stimuli (strings, winds, and brass). During a task requiring attending to a feature other than timbre, voices were not distinguished from voicelike stimuli (strings), but were distinguished from other harmonic stimuli. We suggest that the component elicited by voices and similar sounds reflects the allocation of attention on the basis of stimulus significance (as opposed to novelty), and propose an explanation of the task and attentional factors that contribute to the effect.

Electrophysiological evidence of abnormal activation of the cerebral network of involuntary attention in alcoholism

OBJECTIVE

Increased distractibility is a common impairment in alcoholism, but objective evidence has remained elusive. Here, a task designed to investigate with event-related brain potentials (ERPs) the neural mechanism underlying distraction was used to show abnormal involuntary orienting of attention in chronic alcoholism.

METHODS

Fifteen alcoholics and 17 matched healthy controls were instructed to ignore auditory stimuli while concentrating in the discrimination of immediately following visual stimuli. The auditory sequences contained repetitive standard tones occasionally replaced by deviant tones of slightly higher frequency, or by complex novel sounds.

RESULTS

Deviant tones and novel sounds distracted visual performance, i.e. increased reaction time to visual stimuli, similarly in patients and controls. Compared to controls, however, alcoholics showed ERP abnormalities, i.e. enhanced P3a amplitudes over the left frontal region, and a positive posterior deflection instead of the frontally distributed reorienting negativity (RON).

CONCLUSIONS

The enhanced P3a to novelty and subsequent positive wave instead of RON in alcoholics suggests encoding into working memory of task-irrelevant auditory events and provides neurophysiological markers of impaired involuntary attention mechanisms in chronic alcoholism.

Event-related potential measures of the inhibition of information processing: II. The sleep onset period

The loss of consciousness during the sleep onset period is associated with dramatic changes in information processing. Human event-related potentials (ERPs) reflect these changes. Short- and mid-latency ERPs are only minimally affected by sleep onset. On the other hand, long-latency ERPs are very much affected. A negative wave, N1, peaking at approximately 100 ms gradually decreases in amplitude until it reaches baseline level during definitive stage 2 sleep. The changes in N1 are especially apparent when the subject no longer signals awareness of the external stimulus or when stage 1 is dominated by theta activity in the EEG. The positive peaks, P1 and P2, peaking at approximately 50 and 180 ms, respectively, may appear to increase in amplitude (i.e. also be less negative). A long-lasting processing negativity (PN) may overlap and summate with these peaks during the waking state. During sleep onset, the PN dissipates, thus explaining the apparent positive baseline shift in the ERP waveform. In an oddball task, when an alert and awake subject detects a rare, relevant stimulus, a large positive wave, P300, maximum over parietal areas of the scalp, is observed. This P300 is, however, widely dispersed and can be observed over frontal areas of the scalp. When the subject no longer signals detection of this target stimulus, P300 can no longer be recorded. During stage 1, the parietal P300 remains large, providing the subject overtly detects the target. The amplitude of the frontal aspect of P300 is much reduced as response times slow. This may reflect deactivation of the frontal lobes during the sleep onset period. The infrequent change of an otherwise rapidly presented homogenous train of stimuli is associated with another long-lasting negativity, the mismatch negativity (MMN). The MMN also decreases in amplitude during the sleep onset period, reaching baseline level during definitive sleep. The vertex sharp wave (VSW) becomes apparent during the sleep onset period. Associated with the VSW is a late negative ERP, sometimes called the sleep N2 or the N350, peaking between 300 and 350 ms. It is unique to the sleep onset and sleep periods, becoming very large during stage 1-theta or when the subject no longer shows signs of awareness of the external stimulus.

Event-related potential measures of the inhibition of information processing: I. Selective attention in the waking state

This article reviews the effects of selective attention on event-related potentials (ERPs). Attention has little, if any, effect on short-latency exogenous ERPs. The longer-latency ERPs can be markedly affected by manipulation of the subject's level of attention. For example, a late positive wave, P300, appears to occur only if subjects actively detect an infrequently occurring target stimulus. However, a number of other late positive waves may also occur independently of the direction of attention, particularly if elicited by highly biologically or psychologically relevant stimuli. Attention may also interact with an earlier, apparently exogenous, negative waveform, N1. This could be due to the overlapping and summating effect of an attentional-related waveform, the processing negativity. The presentation of a physically deviant stimulus occurring among a train of homogeneous standard stimuli will elicit another negative wave, the mismatch negativity (MMN). The MMN has traditionally been thought to occur independently of attention. More recent studies have, however, shown that attention can modulate the MMN. This may, however, be explained by the summating effects of other overlapping components. Interpreting the scalp-recorded ERP can therefore require judicious care. Design of experiments must take into account the fact that the magnitude of attentional effects will depend on a number of different influences, some of which are very subtle and complex. A problem with any study in the waking and alert human is that the subject may not be able to completely ignore stimuli, in spite of instructions to do so. For this reason, the study of unconscious states, such as sleep, may prove to be especially fruitful in understanding the effects of attention in the waking state.

Dopamine modulates involuntary attention shifting and reorienting: an electromagnetic study

OBJECTIVE

Dopaminergic function has been closely associated with attentional performance, but its precise role has remained elusive.

METHODS

Electrophysiological and behavioral methods were used to assess the effects of dopamine D2-receptor antagonist haloperidol on involuntary attention shifting using a randomized, double-blind, placebo-controlled cross-over design. Eleven subjects were instructed to discriminate equiprobable 200 and 400ms tones in a forced-choice reaction-time (RT) task during simultaneous measurement of whole-head magnetoencephalography and high-resolution electroencephalography.

RESULTS

Occasional changes in task-irrelevant tone frequency (10% increase or decrease) caused marked distraction on behavioral performance, as shown by significant RT increases to deviant stimuli and subsequent standard tones. Furthermore, while the standard tones elicited distinct P1-N1-P2-N2-P3 waveforms, deviant tones elicited additional mismatch negativity (MMN), P3a, and reorienting negativity (RON) responses, indexing brain events associated with involuntary attention shifting. While haloperidol did not affect the source loci of the responses of magnetic N1 and MMN, the amplitude of the electric P3a and that of RON were significantly reduced and the latency of magnetic RON were delayed following haloperidol administration.

CONCLUSIONS

The present results suggest that dopamine modulates involuntary attention shifting to task-irrelevant deviant events. It appears that dopamine may disrupt the subsequent re-orienting efforts to the relevant task after distraction.

An electrophysiological and behavioral investigation of involuntary attention towards auditory frequency, duration and intensity changes

We measured behavior and event-related brain potentials (ERPs) in 12 subjects performing on an audio-visual distraction paradigm to investigate the cerebral mechanisms of involuntary attention towards stimulus changes in the acoustic environment. Subjects classified odd/even numbers presented on a computer screen 300 ms after the occurrence of a task-irrelevant auditory stimulus, by pressing the corresponding response button. Auditory stimuli were standard tones (600 Hz, 200 ms, 85 dB; P=0.8) or deviant tones (P=0.2), these differing from the standard either in frequency (700 Hz), duration (50 ms) or intensity (79 dB), in separate blocks. In comparison to performance to visual stimuli following the standard tones, reaction time increased by 24 ms (F(1,11)=10.91, P<0.01) and hit rate decreased by 4.6% (F(1,11)=35.47, P<0.001) to visual stimuli following the deviant tones, indicating behavioral distraction. ERPs revealed the mismatch negativity (MMN) elicited to deviant tones, which was larger for the duration deviant than for the frequency and intensity deviants (F(2,22)=19.43, P<0.001, epsilon =0.83), and which had different scalp distribution for all three deviant conditions (F(16,176)=2.40, P<0.05, epsilon =0.12). As the shorter duration and softer intensity deviant tones were unlikely to engage fresh neurons responding to their specific physical features, the present results indicate that a genuine change detection mechanism is involved in triggering attention switching towards sound changes, and suggest a largely distributed neural network of the auditory cortex underlying such involuntary attention switching.

Attentional modulation of the nociceptive processing into the human brain: selective spatial attention, probability of stimulus occurrence, and target detection effects on laser evoked potentials

Laser evoked potentials (LEPs) are brain responses to activation of skin nociceptors by laser heat stimuli. LEPs consist of three components: N1, N2, and P2. Previous reports have suggested that in contrast to earlier activities (N1), LEPs responses after 230-250 ms (N2-P2) are modulated by attention to painful laser stimuli. However, the experimental paradigms used were not designed to specify the attentional processes involved in these LEP modulations. We investigated the effects of selective spatial attention and oddball tasks on LEPs. CO(2) laser stimuli of two different intensities were delivered on the dorsum of both hands of ten subjects. One intensity was frequently presented, and the other rarely. Subjects were asked to pay attention to stimuli delivered on one hand and to count rare stimuli, while ignoring stimuli on the other hand. Frequent and rare attended stimuli evoked enhanced N160 (N1) and N230 (N2) components in comparison to LEPs from unattended stimuli. Both components showed scalp distribution contralateral to the stimulus location. The vertex P400 (P2) was unaffected by spatial attention and stimulus location, but its amplitude increased after rare stimuli, whether attended or unattended. An additional parietal P600 component was induced by the attended rare stimuli. It is suggested that several attentional processes can modify nociceptive processing in the brain at different stages. LEP activities in the time-range of N1 and N2 (120-270 ms) showed evidence of processes modulated by the direction of spatial attention. Conversely, processes underlying P2 (400 ms) were not affected by spatial attention, but by the probability of the stimulus. This probability effect was not due to P3b-related processes that were observed at a later latency (600 ms). Indeed, P600 could be seen as a P3b evoked by conscious detection of rare targets.

Cognitive impairment in amyotrophic lateral sclerosis: evidence from neuropsychological investigation and event-related potentials

The presence of subclinical cognitive impairment in patients with amyotrophic lateral sclerosis (ALS) is investigated using neuropsychological assessment and event-related potential recordings (ERP). An extensive battery of neuropsychological tests assessing the domains of attention, memory, language, visuo-spatial and executive functions were administered to 20 non-demented patients with sporadic ALS and 13 age- and education-matched healthy control subjects. Mismatch negativity (MMN), P3b, P3a (novelty P300) and contingent negative variation (CNV) were recorded. ALS patients were significantly impaired in tests of working memory, sustained attention, response inhibition, naming, verbal fluency and complex visuo-spatial processing. The memory impairment seemed to be secondary to deficits in forming learning strategies and retrieval. In ERP recordings, P3a and P3b amplitudes of ALS patients were lower compared with the controls, P3a latencies were significantly longer and mean CNV amplitudes were higher. These results indicate subclinical impairment of cognitive functions in patients with ALS. The pattern of cognitive impairment suggests the dysfunction of the frontal network.

Modulation of mismatch negativity by stimulus deviance and modality of attention

We studied the effect of attention on the processing of auditory sensory inputs by means of the mismatch negativity (MMN) potential, which can be derived from event-related EEG. A series of frequent standard and rare deviant auditory stimuli were presented to 20 healthy subjects in two recording sessions about five weeks apart. Deviant stimuli were either low or highly deviant as compared to the standard stimulus. While MMN was recorded, subjects were performing a visual and, subsequently, an auditory discrimination task. Directing attention towards the auditory task was associated with increased MMN amplitude only in response to low deviant stimuli and only in the first recording session. No change of MMN amplitude was found when directing attention towards the visual task or when MMN was recorded in response to highly deviant auditory stimuli. The latter may trigger an involuntary switch of attention, thereby overwriting the effect of task-directed attention. Conversely, the effects of attention on the processing of low deviant stimuli appear to be fragile and diminish with increasing automaticity of task execution.

Acute nicotine effects on auditory sensory memory in tacrine-treated and nontreated patients with Alzheimer's disease: an event-related potential study

The auditory mismatch negativity (MMN) event-related brain potential (ERP) reflects the storage of information in acoustic sensory memory. Thirteen patients with Alzheimer's disease (AD), 6 receiving treatment with the cholinesterase inhibitor, tacrine [tetrahydroaminoacridine (THA)], and 7 receiving no treatment, were administered 2 mg of nicotine polacrilex and placebo. MMNs were recorded with 1- and 3-s interstimulus intervals (ISIs) during pre- and post-placebo/nicotine administration. Amplitudes decreased from pre- to post-placebo recordings in nontreated patients but remained stable in THA-treated patients. Comparison of pre- and post-nicotine MMNs found amplitude increases with nicotine in nontreated but not in THA-treated patients. MMN latencies were shortened by nicotine in both treatment groups. These exploratory findings suggest that nicotine-improved strength of acoustic sensory memory traces and speed of acoustic sensory discrimination in AD are differentially affected by chronic tacrine treatment.

Discrimination of emotional facial expressions in a visual oddball task: an ERP study

Several ERP studies have shown an orienting complex, the N2/P3a, associated to the detection of stimulus novelty. Its role consists in preparing the organism to process and react to biologically prepotent stimuli. Whether this N2/P3a: (1) could be obtained with complex visual stimuli, such as with emotional facial expressions; and (2) could take part in a complex discrimination process has yet to be determined. To investigate this issue, event-related potentials were recorded in response to repetitions of a particular facial expression (e.g. sadness) and in response to two different deviant (rare) stimuli, one depicting the same emotion as the frequent stimulus, while the other depicted a different facial expression (e.g. fear). As expected, deviant stimuli evoked an N2/P3a complex of larger amplitude than frequent stimuli. But more interestingly, when the deviant stimulus depicted the same emotion as the frequent stimulus the N2/P3a was delayed compared to the response elicited by the different-emotion deviant. The N2/P3a was thus implicated in the detection of physical facial changes, with a higher sensitivity to changes related to a new different emotional content, perhaps leading to faster adaptive reactions.

Automatic and controlled processing of melodic contour and interval information measured by electrical brain activity

Most work on how pitch is encoded in the auditory cortex has focused on tonotopic (absolute) pitch maps. However, melodic information is thought to be encoded in the brain in two different "relative pitch" forms, a domain-general contour code (up/down pattern of pitch changes) and a music-specific interval code (exact pitch distances between notes). Event-related potentials were analyzed in nonmusicians from both passive and active oddball tasks where either the contour or the interval of melody-final notes was occasionally altered. The occasional deviant notes generated a right frontal positivity peaking around 350 msec and a central parietal P3b peaking around 580 msec that were present only when participants focused their attention on the auditory stimuli. Both types of melodic information were encoded automatically in the absence of absolute pitch cues, as indexed by a mismatch negativity wave recorded during the passive conditions. The results indicate that even in the absence of musical training, the brain is set up to automatically encode music-specific melodic information, even when absolute pitch information is not available.

A modified oddball paradigm "cross-modal delayed response" and the research on mismatch negativity

A modified oddball paradigm was developed to facilitate the focus of attention and to minimize target effects on deviant-related components of auditory and visual event-related potentials (ERPs) elicited with long interstimulus intervals. Subjects were required to focus on either the visual or auditory stimulus in each stimulus block. Deviant-related components were obtained by subtracting ERPs of the standard stimulus from that of the deviant stimulus for each modality with each stimulus condition. Results showed that auditory mismatch negativity (MMN) and a visual early deviant related negativity (DRN1) were elicited both when stimuli were attended and unattended. In contrast, N2b and P3 were produced only under the attended condition. In comparison of attended MMN and unattended MMN at three time windows (100-150 ms, 150-200 ms, and 200-250 ms) of MMN zone, different scalp distributions were shown, depending on the time windows. This result suggests that the attended auditory MMN is a mixed wave, consisting of genuine MMN, N2b, and possible P165. The effect of attention on MMN may stem from the contamination of these overlapping components. With the present paradigm, at least three sensory memory traces have to be maintained simultaneously in multiple sensory modalities to support automatic processing.

Changes in event-related potentials in a three-stimulus auditory oddball task after mild head injury

Previous research has demonstrated changes in event-related potentials in a variety of cognitive tasks after severe closed head injury. We sought to establish if similar changes were present in patients who had sustained only apparently mild head injury (MHI) by recording event-related potentials in a group of 24 mild head injured and 24 control participants during a three-stimulus auditory target detection task. For this "oddball" task participants were required to press a button every time they heard a rare target tone and to ignore rare novel sounds and frequent non-target tones. Neuropsychological test results indicated that the mild head injured group had mild memory and attention impairments. Analysis of behavioural performance on the three-stimulus "oddball" task showed no difference in reaction times or error rates between the two groups. Target condition N2 deflections appeared to be larger in the mild head injured but peak amplitude measures revealed that this effect was not significant. There were no significant differences in the amplitude or latency of the P3b evoked by target stimuli or the P3a evoked by novel stimuli. However, a putative "O-wave" or "reorienting negativity" following the P3a was more negative in the mild head injured group suggesting increased activation of components of the attention network. These findings lend support to the hypothesis that MHI can cause subtle cognitive impairments that are associated with abnormal allocation of attention resources in the context of normal behavioural performance.

Involuntary attention in children as a function of sound source location: evidence from event-related potentials

OBJECTIVES

The present study addressed the question of whether location of the auditory stimulation source affects an involuntary attention triggering to the deviant sounds in a passive oddball paradigm in 8-10-year-old children.

METHODS

Using free-field stimulation two late event-related potentials components were examined: the mismatch negativity (MMN), indexing preconscious sound change detection and the P3a, indexing involuntary attention switch. Data were registered to frequency changes in sounds of different complexities in two experimental conditions. In the 'in-front' condition, the sound sequences were presented through the loudspeakers situated in front of a participant on both sides of the video display. In the 'on-sides' condition, the sources of auditory and visual stimuli were separated by moving the loudspeakers to the sides of the participant.

RESULTS

The MMN amplitude or the MMN and P3a latencies varied in neither stimulus class significantly as a function of sound location. However, significantly larger P3 amplitude was found in the 'in-front', as compared to the 'on-sides' condition.

CONCLUSIONS

The present results indicate enhanced involuntary attention switching in children when unattended auditory events occur within the space attended actively for visual modality. Such study design favouring cross-modal integration can be advantageous when studying involuntary auditory attention and its impairment in children.

Human Event-Related Potentials to Higher-Order Acoustic Spatial Changes

Abstract Human event-related potentials (ERPs) to a tone continuously alternating between its two spatial loci of origin (middle-standards, left-standards), to repetitions of left-standards (oddball-deviants), and to the tones originally representing these repetitions presented alone (alone-deviants) were recorded in free-field conditions. During the recordings (Fz, Cz, Pz, M1, and M2 referenced to nose), the subjects watched a silent movie. Oddball-deviants elicited a spatially diffuse two-peaked deflection of positive polarity. It differed from a deflection elicited by left-standards and commenced earlier than a prominent deflection of negative polarity (N1) elicited by alone-deviants. The results are discussed in the context of the mismatch negativity (MMN) and previous findings of dissociation between spatial and non-spatial information in auditory working memory.

Differential contribution of frontal and temporal cortices to auditory change detection: fMRI and ERP results

The present study addresses the functional role of the temporal and frontal lobes in auditory change detection. Prior event-related potential (ERP) research suggested that the mismatch negativity (MMN) reflects the involvement of a temporofrontal network subserving auditory change detection processes and the initiation of an involuntary attention switch. In the present study participants were presented with repetitive spectrally rich sounds. Infrequent changes of either small (10% change), medium (30% change), or large (100% change) magnitude were embedded in the stimulus train. ERPs and fMRI measures were obtained in the same subjects in subsequent sessions. Significant hemodynamic activation in the superior temporal gyri (STG) bilaterally and the opercular part of the right inferior frontal gyrus was observed for large and medium deviants only. ERPs showed that small deviants elicited MMN when presented in silence but not when presented with recorded MR background noise, indicating that small deviants were hardly detected under fMRI conditions. The MR signal change in temporal lobe regions was larger for large than for medium deviants. For the right fronto-opercular cortex the opposite pattern was observed. The strength of the temporal activation correlated with the amplitude of the change-related ERP at around 110 ms from stimulus onset while the frontal activation correlated with the change-related ERP at around 150 ms. These results suggest that the right fronto-opercular cortex is part of the neural network generating the MMN. Three alternative explanations of these findings are discussed.

Activation of brain mechanisms of attention switching as a function of auditory frequency change

The activation of the cerebral network underlying involuntary attention switching was studied as a function of the magnitude of auditory change. Event-related brain potentials (ERPs) were recorded during the performance of a visual discrimination task in which task-irrelevant auditory frequency changes of six different levels (5%, 10%, 15%, 20%, 40% and 80%) occurred randomly within the same stimulus sequence. All the frequency changes elicited a typical ERP waveform, characterized by MMN, P3a and RON, their respective amplitudes increasing linearly as a function of the magnitude of change. The results indicate that attentional processes in the brain may follow a linear function of activation, contrasting with the well-established logarithmic functions underlying perceptual and psychophysical processes.

Modulation of startle and the startle-elicited P300 by the conditions of the cued continuous performance task in school-age boys

OBJECTIVES

This study compares the modulation of the startle response by conditions requiring response preparation, production, and inhibition during a cued continuous performance task (CPT) in children to the results of previous studies in adults and evaluates the modulation of the startle-elicited P300 under the same conditions. The latter variable, reflecting the cognitive processing of the startling stimulus (SS), has not been studied under these conditions.

METHODS

Normal boys completed a cued CPT in which the cue was the letter T, the go condition requiring a button press was an X following the T, and the no-go condition requiring response inhibition was a letter other than X following the T. SS were presented 450 ms following the letter of interest in each condition. The amplitudes of the startle-elicited P300 at Fz, Cz, and Pz and the startle blink were compared in the different CPT conditions.

RESULTS

The startle blink, measured by orbicularis oculi electromyography, was not inhibited by the no-go CPT condition as is the case in adults. The vertical electro-oculogram was actually largest in the no-go condition. The startle-elicited P300 showed a central predominance and was significantly larger in the no-go condition and in the cue condition than in the go condition.

CONCLUSIONS

The absence of inhibition of the startle response during the no-go condition probably reflects a relative inefficiency of prefrontal cortical mechanisms that mediate response inhibition in children compared to adults. The enhanced startle-elicited P300 in the no-go and cue conditions of the CPT reflects cognitive processing of the SS that has been influenced by response inhibition or its anticipation.

Brain activity index of distractibility in normal school-age children

Children's attention is easily diverted from a current activity to a new event in the environment. This was indexed in school-age children by diminished performance speed and accuracy in a visual discrimination task caused by task-irrelevant novel sounds. Event-related brain potentials (ERPs) elicited by these distracting sounds showed a prominent positive deflection that was generated by brain processes associated with involuntary switching of attention to novel sounds. Recordings of the magnetoencephalographic (MEG) counterpart of this brain activity revealed a major bilateral generator source in the superior temporal cortex. However, ERP scalp distributions indicated also overlapping brain activity generated in other brain areas involved in involuntary attention switching. Moreover, differences in ERP amplitudes and in their correlations with the reaction times between younger (7-10 years) and older (11-13 years) children indicated developmental changes in attentional brain functions.

The decade 1989-1998 in Spanish psychology: an analysis of research in psychobiology

In this paper, we present an analysis of the research published during the 1989-1998 decade by tenured Spanish faculty members from the area of psychobiology. Database search and direct correspondence with the 110 faculty members rendered a list of 904 psychobiological papers. Classification and analysis of these papers led to the definition of at least 70 different research trends. Topics are grouped into several specific research areas: Learning and Memory; Development and Neural Plasticity; Emotion and Stress; Ethology; Neuropsychology; Sensory Processing; and Psychopharmacology. The international dissemination of this research, published in journals of high impact index, and the increasing number of papers are two noteworthy features.

ERP and EOG responses elicited by deviant tones when presented with and without standard tones to reading subjects

Event-related potentials (ERPs) and horizontal electro-oculograms (HEOGs) were recorded in 11 subjects to infrequently presented spatially deviant tones (oddball-deviants) embedded in a series of frequently presented standard tones and also to these deviant tones when presented without the standard tones (alone-deviants). Subjects were instructed to read a self-selected book during the stimulus presentation. The mismatch negativity (MMN), a component of the ERP, was elicited by the oddball-deviants, whereas ERPs to the alone-deviants were characterized by a prominent N1. In an additional counting condition (subjects counting the oddball-deviants), the MMN to the oddball-deviants was followed by the P3b. Although the effects of pre-attentive and attentive processing of the oddball-deviants were evident in the ERPs, HEOGs were affected by these stimuli in neither reading nor counting condition. In contrast, robust HEOG responses were elicited by the alone-deviants in the reading condition. The results suggest that reading is a sufficiently demanding task to enable the subject to effectively ignore the oddball-deviants but not the alone-deviants.

Auditory information processing during human sleep as revealed by event-related brain potentials

The main goal of this review is to elucidate up to what extent pre-attentive auditory information processing is affected during human sleep. Evidence from event-related brain potential (ERP) studies indicates that auditory information processing is selectively affected, even at early phases, across the different stages of sleep-wakefulness continuum. According to these studies, 3 main conclusions are drawn: (1) the sleeping brain is able to automatically detect stimulus occurrence and trigger an orienting response towards that stimulus if its degree of novelty is large; (2) auditory stimuli are represented in the auditory system and maintained for a period of time in sensory memory, making the automatic-change detection during sleep possible; and (3) there are specific brain mechanisms (sleep-specific ERP components associated with the presence of vertex waves and K-complexes) by which information processing can be improved during non-rapid eye movement sleep. However, the remarkably affected amplitude and latency of the waking-ERPs during the different stages of sleep suggests deficits in the building and maintenance of a neural representation of the stimulus as well as in the process by which neural events lead to an orienting response toward such a stimulus. The deactivation of areas in the dorsolateral pre-frontal cortex during sleep contributing to the generation of these ERP components is hypothesized to be one of the main causes for the attenuated amplitude of these ERPs during human sleep.

Capture of attention in selective frequency listening

Four signal-detection experiments demonstrated robust stimulus-driven, or exogenous, attentional processes in selective frequency listening. Detection of just-above-threshold signal tones was consistently better when the, signal matched the frequency of an uninformative cue tone, even with relatively long cue-signal delays (Experiment 1) or when as few as 1 in 8 signals were at the cued frequency (Experiment 2). Experiments 3 and 4 compared performance with informative and uninformative cues. The involvement of intentional, or endogenous, processes was found to only slightly increase the size of the cuing effect beyond that evident with solely exogenous processes, although the attention band, a measure of how narrowly attention is focused, was found to be wider when cues were informative. The implications for models of auditory attention are discussed.

Electrical responses reveal the temporal dynamics of brain events during involuntary attention switching

Surviving in the natural environment requires the rapid switching of attention among potentially relevant stimuli. We studied electrophysiologically the involuntary switching time in humans performing a task designed to study brain mechanisms of involuntary attention and distraction (C. Escera et al., 1998, J. Cogn. Neurosci., 10, 590-604). Ten subjects were instructed to discriminate visual stimuli preceded by a task-irrelevant sound, this being either a repetitive tone (P = 0.8) or a distracting sound, i.e. a slightly higher deviant tone (P = 0.1) or an environmental novel sound (P = 0.1). In different conditions, the sounds preceded the visual stimuli by 245 or 355 ms. Deviant tones and novel sounds prolonged reaction times significantly to subsequent visual stimuli by 7.4 (P < 0.02) and 15.2 ms (P < 0.003), respectively. In addition to a mismatch negativity (MMN) and a positive-polarity, 320-ms latency, P3a event-related potential associated, respectively, with detection of the distracting sound and the subsequent orienting of attention to it, a late frontal negative deflection was observed in distracting trials. The peak latency of this brain response from sound onset was 580 ms in the 245-ms condition and 115 ms longer in the 355-ms condition (P < 0.001), peaking consequently at 340 ms from visual stimulus onset, irrespective of the onset of the distracting sound. We suggest that this late frontal negative response may signal over the scalp the process of reallocating attention back to the original task after momentary distraction, and therefore that recovering from distraction may take a similar shifting time as orienting attention involuntarily towards unexpected novelty.

Measuring temporal resolution in infants using mismatch negativity

We show that the mismatch negativity (MMN) component of the event-related potential can be used to measure auditory temporal resolution in human infants. Infrequent stimuli with silent gaps of 4, 8, or 12 ms modulated the P2 component, generated MMN, and produced a P3a-like positivity. The data indicate that within-channel gap detection thresholds at 6 months are essentially at adult levels under conditions of little adaptation. Since MMN is elicited without attention and does not require a behavioural response, it can be measured similarly across the lifespan. We are now in a position to study the development of cross-channel temporal resolution and adaptation effects in infancy, and to examine how these abilities in infancy relate to later language acquisition.

Cerebral mechanisms underlying orienting of attention towards auditory frequency changes

Brain mechanisms underlying detection of auditory frequency changes were studied with event-related potentials (ERPs) in 14 human subjects discriminating visual stimuli. Scalp-current density mapping revealed bilateral components of mismatch negativity (MMN) in frontal and auditory cortices. Deviance-related activations in frontal and temporal cortex began to be significant at 94 ms and 154 ms in the right hemisphere, and at 128 ms and 132 ms in the left hemisphere. The magnitude of MMN-neuroelectric currents from the left temporal cortex correlated significantly (r = -0.56, p < 0.05) with distraction caused by MMN-eliciting deviant tones. These results suggest a complex cerebral circuitry involved in frequency change detection and strongly support the role of this circuitry in driving attention involuntarily towards potentially relevant frequency changes in the acoustic environment.

Effects of acoustic gradient noise from functional magnetic resonance imaging on auditory processing as reflected by event-related brain potentials

The processing of sound changes and involuntary attention to them has been widely studied with event-related brain potentials (ERPs). Recently, functional magnetic resonance imaging (fMRI) has been applied to determine the neural mechanisms of involuntary attention and the sources of the corresponding ERP components. The gradient-coil switching noise from the MRI scanner, however, is a challenge to any experimental design using auditory stimuli. In the present study, the effects of MRI noise on ERPs associated with preattentive processing of sound changes and involuntary switching of attention to them were investigated. Auditory stimuli consisted of frequently presented "standard" sounds, infrequent, slightly higher "deviant" sounds, and infrequent natural "novel" sounds. The standard and deviant sounds were either sinusoidal tones or musical chords, in separate stimulus sequences. The mismatch negativity (MMN) ERP associated with preattentive sound change detection was elicited by the deviant and novel sounds and was not affected by the prerecorded background MRI noise (in comparison with the condition with no background noise). The succeeding positive P3a ERP responses associated with involuntary attention switching elicited by novel sounds were also not affected by the MRI noise. However, in ERPs to standard tones and chords, the P1, N1, and P2 peak latencies were significantly prolonged by the MRI noise. Moreover, the amplitude of the subsequent "exogenous" N2 to the standard sounds was significantly attenuated by the presence of MRI noise. In conclusion, the present results suggest that in fMRI the background noise does not interfere with the imaging of auditory processing related to involuntary attention.

The novelty P3: an event-related brain potential (ERP) sign of the brain's evaluation of novelty

A review of the literature that examines event-related brain potentials (ERPs) and novelty processing reveals that the orienting response engendered by deviant or unexpected events consists of a characteristic ERP pattern, comprised sequentially of the mismatch negativity (MMN) and the novelty P3 or P3a. A wide variety of evidence suggests that the MMN reflects the detection of deviant events, whereas the P3a is associated more with the evaluation of those events for subsequent behavioral action. On the scalp, the novelty P3a is comprised of at least two aspects, one frontal the other posterior, each with different cognitive (and presumably neurologic) correlates. Intracranial ERP investigations and studies of patients with localized brain lesions (and, to some extent, fMRI data) converge with the scalp-recorded data in suggesting a widespread neural network, the different aspects of which respond differentially to stimulus and task characteristics.

The initial orienting response during human REM sleep as revealed by the N1 component of auditory event-related potentials

The large N1 wave of the auditory event-related potentials (ERPs) typically occurring to the first stimulus after a long silent interval seems to be associated with the involuntary initial-orienting response. Since the mechanisms involved in the generation of this brain response are assumed to be activated automatically, the present study aims at determining whether this electrophysiological response can also be elicited during human REM sleep, the sleep stage considered most sensitive to external stimuli. To achieve this goal, the auditory N1 wave was analyzed in wakefulness and REM sleep for frequency deviant tones delivered in several positions (1, 2, 4 and 6) within homogenous stimulus trains separated by different intervals of silence (3, 6 and 9 s), the intra-train stimulus interval being 600 ms. A significant increment in the amplitude of the N1 component for the first deviant tone, as compared with deviants delivered in remaining positions, was observed in both brain states, independently of the inter-train interval length. This result cannot be explained by a release-from-refractoriness effect, since only one deviant was presented in each train and the inter-deviant interval hardly changed from one train to another. The increase in N1 to the first stimulus of the train, probably due to the contribution of the neuronal elements responsible for the supratemporal and non-specific components, may be explained by changes in the silent interval, rather than by variations in the stimulus frequency. The enhanced N1 could be reflecting a general increase in sensory sensitivity associated with the arousal factor of the orienting response. These findings suggest that the brain maintains the potential ability to trigger the brain events responsible for the OR elicitation, even during REM sleep.

Intracranial identification of an electric frontal-cortex response to auditory stimulus change: a case study

The aim of the present study was to clarify whether ERPs recorded directly from the human frontal cortex contributed to the auditory N1 and mismatch negativity (MMN) elicited by changes in non-phonetic and phonetic sounds. We examined the role of prefrontal cortex in the processing of stimulus repetition and change in a 6-year-old child undergoing presurgical evaluation for epilepsy. EEG was recorded from three bilateral sub-dural electrode strips located over lateral prefrontal areas during unattended auditory stimulation. EEG epochs were averaged to obtain event-related potentials (ERPs) to repeating (standard) tones and to infrequent (deviant) shorter duration tones and complex sounds (telephone buzz). In another condition, ERPs were recorded to standard and deviant syllables, /ba/ and /da/, respectively. ERPs to vibration stimuli delivered to the fingertips were not observed at any of the sub-dural electrodes, confirming modality specificity of the auditory responses. Focal auditory ERPs consisting of P100 and N150 deflections were recorded to both tones and phonemes over the right lateral prefrontal cortex. These responses were insensitive to the serial position of the repeating sound in the stimulus train. Deviant tones evoked an MMN peaking at around 128 ms. Deviant complex sounds evoked ERPs with a similar onset latency and morphology but with an approximately two-fold increase in peak-to-peak amplitude. We conclude that right lateral prefrontal cortex (Brodmann's area 45) is involved in early stages of processing repeating sounds and sound changes.