Spatio-temporal distribution of brain activity associated with audio-visually congruent and incongruent speech and the McGurk Effect.

INTRODUCTION: Spatio-temporal distributions of cortical activity to audio-visual presentations of meaningless vowel-consonant-vowels and the effects of audio-visual congruence/incongruence, with emphasis on the McGurk effect, were studied. The McGurk effect occurs when a clearly audible syllable with one consonant, is presented simultaneously with a visual presentation of a face articulating a syllable with a different consonant and the resulting percept is a syllable with a consonant other than the auditorily presented one. METHODS: Twenty subjects listened to pairs of audio-visually congruent or incongruent utterances and indicated whether pair members were the same or not. Source current densities of event-related potentials to the first utterance in the pair were estimated and effects of stimulus-response combinations, brain area, hemisphere, and clarity of visual articulation were assessed. RESULTS: Auditory cortex, superior parietal cortex, and middle temporal cortex were the most consistently involved areas across experimental conditions. Early (<200 msec) processing of the consonant was overall prominent in the left hemisphere, except right hemisphere prominence in superior parietal cortex and secondary visual cortex. Clarity of visual articulation impacted activity in secondary visual cortex and Wernicke's area. McGurk perception was associated with decreased activity in primary and secondary auditory cortices and Wernicke's area before 100 msec, increased activity around 100 msec which decreased again around 180 msec. Activity in Broca's area was unaffected by McGurk perception and was only increased to congruent audio-visual stimuli 30-70 msec following consonant onset. CONCLUSIONS: The results suggest left hemisphere prominence in the effects of stimulus and response conditions on eight brain areas involved in dynamically distributed parallel processing of audio-visual integration. Initially (30-70 msec) subcortical contributions to auditory cortex, superior parietal cortex, and middle temporal cortex occur. During 100-140 msec, peristriate visual influences and Wernicke's area join in the processing. Resolution of incongruent audio-visual inputs is then attempted, and if successful, McGurk perception occurs and cortical activity in left hemisphere further increases between 170 and 260 msec.

Natural stimuli from three coherent modalities enhance behavioral responses and electrophysiological cortical activity in humans.

Cues that involve a number of sensory modalities are processed in the brain in an interactive multimodal manner rather than independently for each modality. We studied multimodal integration in a natural, yet fully controlled scene, implemented as an interactive game in an auditory-haptic-visual virtual environment. In this imitation of a natural scene, the targets of perception were ecologically valid uni-, bi- and tri-modal manifestations of a simple event-a ball hitting a wall. Subjects were engaged in the game while their behavioral and early cortical electrophysiological responses were measured. Behavioral results confirmed that tri-modal cues were detected faster and more accurately than bi-modal cues, which, likewise, showed advantages over unimodal responses. Event-Related Potentials (ERPs) were recorded, and the first 200 ms following stimulus onset was analyzed to reveal the latencies of cortical multimodal interactions as estimated by sLORETA. These electrophysiological findings indicated bi-modal as well as tri-modal interactions beginning very early (~30 ms), uniquely for each multimodal combination. The results suggest that early cortical multimodal integration accelerates cortical activity and, in turn, enhances performance measures. This acceleration registers on the scalp as sub-additive cortical activation.

Auditory cortical activity in normal hearing subjects to consonant vowels presented in quiet and in noise.

OBJECTIVE: Compare brain potentials to consonant vowels (CVs) as a function of both voice onset times (VOTs) and consonant position; initial (CV) versus second (VCV). METHODS: Auditory cortical potentials (N100, P200, N200, and a late slow negativity, (SN) were recorded from scalp electrodes in twelve normal hearing subjects to consonant vowels in initial position (CVs: /du/ and /tu/), in second position (VCVs: /udu/ and /utu/), and to vowels alone (V: /u/) and paired (VVs: /uu/) separated in time to simulate consonant voice onset times (VOTs). RESULTS: CVs evoked "acoustic onset" N100s of similar latency but larger amplitudes to /du/ than /tu/. CVs preceded by a vowel (VCVs) evoked "acoustic change" N100s with longer latencies to /utu/ than /udu/. Their absolute latency difference was less than the corresponding VOT difference. The SN following N100 to VCVs was larger to /utu/ than /udu/. Paired vowels (/uu/) separated by intervals corresponding to consonant VOTs evoked N100s with latency differences equal to the simulated VOT differences and SNs of similar amplitudes. Noise masking resulted in VCV N100 latency differences that were now equal to consonant VOT differences. Brain activations by CVs, VCVs, and VVs were maximal in right temporal lobe. CONCLUSION: Auditory cortical activities to CVs are sensitive to: (1) position of the CV in the utterance; (2) VOTs of consonants; and (3) noise masking. SIGNIFICANCE: VOTs of stop consonants affect auditory cortical activities differently as a function of the position of the consonant in the utterance.

Spatiotemporal distribution of cortical processing of first and second languages in bilinguals. II. Effects of phonologic and semantic priming.

This study determined the effects of phonology and semantics on the distribution of cortical activity to the second of a pair of words in first and second language (mixed pairs). The effects of relative proficiency in the two languages and linguistic setting (monolinguistic or mixed) are reported in a companion paper. Ten early bilinguals and 14 late bilinguals listened to mixed pairs of words in Arabic (L1) and Hebrew (L2) and indicated whether both words in the pair had the same or different meanings. The spatio-temporal distribution of current densities of event-related potentials were estimated for each language and according to semantic and phonologic relationship (same or different) compared with the first word in the pair. During early processing (<300 ms), brain activity in temporal and temporoparietal auditory areas was enhanced by phonologic incongruence between words in the pair and in Wernicke's area by both phonologic and semantic priming. In contrast, brain activities during late processing (>300 ms) were enhanced by semantic incongruence between the two words, particularly in temporal areas and in left hemisphere Broca's and Wernicke's areas. The latter differences were greater when words were in L2. Surprisingly, no significant effects of relative proficiency on processing the second word in the pair were found. These results indicate that the distribution of brain activity to the second of two words presented bilingually is affected differently during early and late processing by both semantic and phonologic priming by- and incongruence with the immediately preceding word.

Dis-regulation of response inhibition in adult Attention Deficit Hyperactivity Disorder (ADHD): an ERP study.

OBJECTIVE: To define the brain activity involved in impaired response inhibition of Attention Deficit Hyperactivity Disorder (ADHD) in adults. METHODS: Performance measures and brain activity of 14 adult ADHD subjects and 14 controls, matched for age, gender, and overall intelligence were compared in an auditory Go-NoGo paradigm to tones. The task required a button press (Go) to 80% and inhibition of response (NoGo) to 20% of the tones, according to the tone's pitch. RESULTS: In NoGo trials ADHD subjects made significantly more commission errors compared to controls. ERPs of ADHD subjects showed smaller amplitudes of P3 (but not N2), and longer latencies of both N2 and P3. Source current density estimation revealed reduced activity in the right frontal dorsolateral cortex and in the posterior cingulate of the ADHD group. In addition, ADHD subjects showed an unexpected significantly enhanced response inhibition in Go trials, with excessive omission errors associated with significantly larger N2 amplitudes. CONCLUSION: In ADHD the neural networks sub-serving response inhibition are impaired. SIGNIFICANCE: ADHD is a general dis-regulation of behavioral inhibition, not limited to response inhibition.

Pseudobulbar affect: the spectrum of clinical presentations, etiologies and treatments.

Pseudobulbar affect (PBA) consists of uncontrollable outbursts of laughter or crying inappropriate to the patient's external circumstances and incongruent with the patient's internal emotional state. Recent data suggest disruption of cortico-pontine-cerebellar circuits, reducing the threshold for motor expression of emotion. Disruption of the microcircuitry of the cerebellum itself may likewise impair its ability to act as a gate-control for emotional expression. Current evidence also suggests that serotonergic and glutamatergic neurotransmission play key roles. Although antidepressants have shown benefit, the supportive clinical data have often derived from small numbers of patients and unvalidated measures of PBA severity. Dextromethorphan/quinidine, the first FDA-approved PBA medication, is a novel therapy with antiglutamatergic actions. As life expectancy lengthens and the neurologic settings of PBA become more common, the need for treatment can be expected to increase.

Auditory cortical N100 in pre- and post-synaptic auditory neuropathy to frequency or intensity changes of continuous tones.

OBJECTIVES: Auditory cortical N100s were examined in ten auditory neuropathy (AN) subjects as objective measures of impaired hearing. METHODS: Latencies and amplitudes of N100 in AN to increases of frequency (4-50%) or intensity (4-8 dB) of low (250 Hz) or high (4000 Hz) frequency tones were compared with results from normal-hearing controls. The sites of auditory nerve dysfunction were pre-synaptic (n=3) due to otoferlin mutations causing temperature sensitive deafness, post-synaptic (n=4) affecting other cranial and/or peripheral neuropathies, and undefined (n=3). RESULTS: AN consistently had N100s only to the largest changes of frequency or intensity whereas controls consistently had N100s to all but the smallest frequency and intensity changes. N100 latency in AN was significantly delayed compared to controls, more so for 250 than for 4000 Hz and more so for changes of intensity compared to frequency. N100 amplitudes to frequency change were significantly reduced in ANs compared to controls, except for pre-synaptic AN in whom amplitudes were greater than controls. N100 latency to frequency change of 250 but not of 4000 Hz was significantly related to speech perception scores. CONCLUSIONS: As a group, AN subjects' N100 potentials were abnormally delayed and smaller, particularly for low frequency. The extent of these abnormalities differed between pre- and post-synaptic forms of the disorder. SIGNIFICANCE: Abnormalities of auditory cortical N100 in AN reflect disorders of both temporal processing (low frequency) and neural adaptation (high frequency). Auditory N100 latency to the low frequency provides an objective measure of the degree of impaired speech perception in AN.

Effects of dextromethorphan/quinidine on auditory event-related potentials in multiple sclerosis patients with pseudobulbar affect.

The purpose of this study was to characterize the brain activity and associated cortical structures involved in pseudobulbar affect (PBA), a condition characterized by uncontrollable episodes of laughing and/or crying in patients with multiple sclerosis before and after treatment with dextromethorphan/quinidine (DM/Q). Behavioral responses and event-related potentials (ERPs) in response to subjectively significant and neutral verbal stimuli were recorded from 2 groups: 6 multiple sclerosis patients with PBA before (PBA-preTx) and after (PBA-DM/Q) treatment with DM/Q and 6 healthy control (HC) subjects. Statistical nonparametric mapping comparisons of ERP source current density distributions between groups were conducted for subjectively significant and neutral stimuli separately before and after treatment with DM/Q. Treatment with DM/Q had a normalizing effect on the behavioral responses of PBA patients. Event-related potential waveform comparisons of PBA-preTx and PBA-DM/Q with HC, for both neutral and subjectively significant stimuli, revealed effects on early ERP components. Comparisons between PBA-preTx and HC, in response to subjectively significant stimuli, revealed both early and late effects. Source analysis comparisons between PBA-preTx and PBA-DM/Q indicated distinct activations in areas involved in emotional processing and high-level and associative visual processing in response to neutral stimuli and in areas involved in emotional, somatosensory, primary, and premotor processing in response to subjectively significant stimuli. In most cases, stimuli evoked higher current density in PBA-DM/Q compared with the other groups. In conclusion, differences in brain activity were observed before and after medication. Also, DM/Q administration resulted in normalization of behavioral and electrophysiological measures.

Cortical evoked potentials to an auditory illusion: binaural beats.

OBJECTIVE: To define brain activity corresponding to an auditory illusion of 3 and 6Hz binaural beats in 250Hz or 1000Hz base frequencies, and compare it to the sound onset response. METHODS: Event-Related Potentials (ERPs) were recorded in response to unmodulated tones of 250 or 1000Hz to one ear and 3 or 6Hz higher to the other, creating an illusion of amplitude modulations (beats) of 3Hz and 6Hz, in base frequencies of 250Hz and 1000Hz. Tones were 2000ms in duration and presented with approximately 1s intervals. Latency, amplitude and source current density estimates of ERP components to tone onset and subsequent beats-evoked oscillations were determined and compared across beat frequencies with both base frequencies. RESULTS: All stimuli evoked tone-onset P(50), N(100) and P(200) components followed by oscillations corresponding to the beat frequency, and a subsequent tone-offset complex. Beats-evoked oscillations were higher in amplitude with the low base frequency and to the low beat frequency. Sources of the beats-evoked oscillations across all stimulus conditions located mostly to left lateral and inferior temporal lobe areas in all stimulus conditions. Onset-evoked components were not different across stimulus conditions; P(50) had significantly different sources than the beats-evoked oscillations; and N(100) and P(200) sources located to the same temporal lobe regions as beats-evoked oscillations, but were bilateral and also included frontal and parietal contributions. CONCLUSIONS: Neural activity with slightly different volley frequencies from left and right ear converges and interacts in the central auditory brainstem pathways to generate beats of neural activity to modulate activities in the left temporal lobe, giving rise to the illusion of binaural beats. Cortical potentials recorded to binaural beats are distinct from onset responses. SIGNIFICANCE: Brain activity corresponding to an auditory illusion of low frequency beats can be recorded from the scalp.

Auditory-evoked potentials to frequency increase and decrease of high- and low-frequency tones.

OBJECTIVE: To define cortical brain responses to large and small frequency changes (increase and decrease) of high- and low-frequency tones. METHODS: Event-Related Potentials (ERPs) were recorded in response to a 10% or a 50% frequency increase from 250 or 4000 Hz tones that were approximately 3 s in duration and presented at 500-ms intervals. Frequency increase was followed after 1 s by a decrease back to base frequency. Frequency changes occurred at least 1 s before or after tone onset or offset, respectively. Subjects were not attending to the stimuli. Latency, amplitude and source current density estimates of ERPs were compared across frequency changes. RESULTS: All frequency changes evoked components P(50), N(100), and P(200). N(100) and P(200) had double peaks at bilateral and right temporal sites, respectively. These components were followed by a slow negativity (SN). The constituents of N(100) were predominantly localized to temporo-parietal auditory areas. The potentials and their intracranial distributions were affected by both base frequency (larger potentials to low frequency) and direction of change (larger potentials to increase than decrease), as well as by change magnitude (larger potentials to larger change). The differences between frequency increase and decrease depended on base frequency (smaller difference to high frequency) and were localized to frontal areas. CONCLUSIONS: Brain activity varies according to frequency change direction and magnitude as well as base frequency. SIGNIFICANCE: The effects of base frequency and direction of change may reflect brain networks involved in more complex processing such as speech that are differentially sensitive to frequency modulations of high (consonant discrimination) and low (vowels and prosody) frequencies.

Intensity changes in a continuous tone: auditory cortical potentials comparison with frequency changes.

OBJECTIVES: To examine auditory cortical potentials in normal-hearing subjects to intensity increments in a continuous pure tone at low, mid, and high frequency. METHODS: Electrical scalp potentials were recorded in response to randomly occurring 100 ms intensity increments of continuous 250, 1000, and 4000 Hz tones every 1.4 s. The magnitude of intensity change varied between 0, 2, 4, 6, and 8 dB above the 80 dB SPL continuous tone. RESULTS: Potentials included N100, P200, and a slow negative (SN) wave. N100 latencies were delayed whereas amplitudes were not affected for 250 Hz compared to 1000 and 4000 Hz. Functions relating the magnitude of the intensity change and N100 latency/amplitude did not differ in their slope among the three frequencies. No consistent relationship between intensity increment and SN was observed. Cortical dipole sources for N100 did not differ in location or orientation between the three frequencies. CONCLUSIONS: The relationship between intensity increments and N100 latency/amplitude did not differ between tonal frequencies. A cortical tonotopic arrangement was not observed for intensity increments. Our results are in contrast to prior studies of brain activities to brief frequency changes showing cortical tonotopic organization. SIGNIFICANCE: These results suggest that intensity and frequency discrimination employ distinct central processes.

Frequency changes in a continuous tone: auditory cortical potentials.

OBJECTIVE: We examined auditory cortical potentials in normal hearing subjects to spectral changes in continuous low and high frequency pure tones. METHODS: Cortical potentials were recorded to increments of frequency from continuous 250 or 4000Hz tones. The magnitude of change was random and varied from 0% to 50% above the base frequency. RESULTS: Potentials consisted of N100, P200 and a slow negative wave (SN). N100 amplitude, latency and dipole magnitude with frequency increments were significantly greater for low compared to high frequencies. Dipole amplitudes were greater in the right than left hemisphere for both base frequencies. The SN amplitude to frequency changes between 4% and 50% was not significantly related to the magnitude of spectral change. CONCLUSIONS: Modulation of N100 amplitude and latency elicited by spectral change is more pronounced with low compared to high frequencies. SIGNIFICANCE: These data provide electrophysiological evidence that central processing of spectral changes in the cortex differs for low and high frequencies. Some of these differences may be related to both temporal- and spectral-based coding at the auditory periphery. Central representation of frequency change may be related to the different temporal windows of integration across frequencies.

Brain responses to verbal stimuli among multiple sclerosis patients with pseudobulbar affect.

PURPOSE: To characterize the brain activity and associated cortical structures involved in pseudobulbar affect (PBA), a condition characterized by uncontrollable episodes of emotional lability in patients with multiple sclerosis (MS). METHODS: Behavioral responses and event related potentials (ERP) in response to subjectively significant and neutral verbal stimuli were recorded from 33 subjects in 3 groups: 1) MS patients with PBA (MS+PBA); 2) MS patients without PBA (MS); 3) Healthy control subjects (HC). Statistical non-parametric mapping comparisons of ERP source current density distributions between groups were conducted separately for subjectively significant and for neutral stimuli. RESULTS: Behavioral responses showed more impulsive performance in patients with PBA. As expected, almost all ERP waveform comparisons between the MS groups and controls were significant. Source analysis indicated significantly distinct activation in MS+PBA in the vicinity of the somatosensory and motor areas in response to neutral stimuli, and at pre-motor and supplementary motor areas in response to subjectively significant stimuli. Both subjectively significant and neutral stimuli evoked higher current density in MS+PBA compared to both other groups. CONCLUSIONS: PBA of MS patients involves cortical structures related to sensory-motor and emotional processing, in addition to overactive involvement of motor cortical areas in response to neutral stimuli. SIGNIFICANCE: These results may suggest that a 'disinhibition' of a "gate control"-type mechanism for emotional expression may lead to the lower emotional expression threshold of pseudobulbar affect.

The auditory P50 component to onset and offset of sound.

OBJECTIVE: The auditory Event-Related Potentials (ERP) of component P50 to sound onset and offset have been reported to be similar, but their magnetic homologue has been reported absent to sound offset. We compared the spatio-temporal distribution of cortical activity during P50 to sound onset and offset, without confounds of spectral change. METHODS: ERPs were recorded in response to onsets and offsets of silent intervals of 0.5 s (gaps) appearing randomly in otherwise continuous white noise and compared to ERPs to randomly distributed click pairs with half second separation presented in silence. Subjects were awake and distracted from the stimuli by reading a complicated text. Measures of P50 included peak latency and amplitude, as well as source current density estimates to the clicks and sound onsets and offsets. RESULTS: P50 occurred in response to noise onsets and to clicks, while to noise offset it was absent. Latency of P50 was similar to noise onset (56 ms) and to clicks (53 ms). Sources of P50 to noise onsets and clicks included bilateral superior parietal areas. In contrast, noise offsets activated left inferior temporal and occipital areas at the time of P50. Source current density was significantly higher to noise onset than offset in the vicinity of the temporo-parietal junction. CONCLUSIONS: P50 to sound offset is absent compared to the distinct P50 to sound onset and to clicks, at different intracranial sources. P50 to stimulus onset and to clicks appears to reflect preattentive arousal by a new sound in the scene. Sound offset does not involve a new sound and hence the absent P50. SIGNIFICANCE: Stimulus onset activates distinct early cortical processes that are absent to offset.

The N1 complex to gaps in noise: effects of preceding noise duration and intensity.

OBJECTIVE: To study the effects of duration and intensity of noise that precedes gaps in noise on the N-Complex (N(1a) and N(1b)) of Event-Related Potentials (ERPs) to the gaps. METHODS: ERPs were recorded from 13 normal subjects in response to 20 ms gaps in 2-4.5 s segments of binaural white noise. Within each segment, the gaps appeared after 500, 1500, 2500 or 4000 ms of noise. Noise intensity was either 75, 60 or 45 dBnHL. Analysis included waveform peak measurements and intracranial source current density estimations, as well as statistical assessment of the effects of pre-gap noise duration and intensity on N(1a) and N(1b) and their estimated intracranial source activity. RESULTS: The N-Complex was detected at about 100 ms under all stimulus conditions. Latencies of N(1a) (at approximately 90 ms) and N(1b) (at approximately 150 ms) were significantly affected by duration of the preceding noise. Both their amplitudes and the latency of N(1b) were affected by the preceding noise intensity. Source current density was most prominent, under all stimulus conditions, in the vicinity of the temporo-parietal junction, with the first peak (N(1a)) lateralized to the left hemisphere and the second peak (N(1b)) - to the right. Additional sources with lower current density were more anterior, with a single peak spanning the duration of the N-Complex. CONCLUSIONS: The N(1a) and N(1b) of the N-Complex of the ERPs to gaps in noise are affected by both duration and intensity of the pre-gap noise. The minimum noise duration required for the appearance of a double-peaked N-Complex is just under 500 ms, depending on noise intensity. N(1a) and N(1b) of the N-Complex are generated predominantly in opposite temporo-parietal brain areas: N(1a) on the left and N(1b) on the right. SIGNIFICANCE: Duration and intensity interact to define the dual peaked N-Complex, signaling the cessation of an ongoing sound.

The composite N1 component to gaps in noise.

OBJECTIVE: To indicate whether the double peaked N(1) to gaps in continuous white noise is a composite of onset and offset responses to transients or whether it reflects higher processing such as change or mismatch detection and to assess the role of attention in this process. METHODS: Evoked potentials were recorded to two binaural stimulus types: (1) gaps of different durations randomly distributed in continuous white noise; and (2) click pairs at intervals identical to those between gap onsets and offsets in the continuous noise stimulus. Potentials to these stimuli were recorded while subjects read a text and while detecting gaps in noise or click pairs. RESULTS: Potentials were detected to all click pairs and to gaps of 5 ms or longer, corresponding to the subjects' psychoacoustic gap detection threshold. With long gap durations of 200-800 ms, distinct potentials to gap onset and gap offset were observed. The waveforms to all click pairs and to offsets of long gaps were similar and single-peaked, while potentials to gaps of 10 ms and longer, and potentials to onsets of long gaps were double-peaked, consisting of two N(1) negativities, 60 ms apart, irrespective of gap duration. The first (N(1a)), was more frontal in its distribution and similar to that of clicks. The second (N(1b)) peak's distribution was more central/temporal and its source locations and time course of activity were distinct. No effects of attention on any of the varieties and constituents of N(1) were observed. CONCLUSIONS: Comparing potentials to gap onsets, to click pairs and to gap offsets, suggests that potentials to gap onsets involve not only sound onset/offset responses (N(1), N(1a)) but also the subsequent pre-attentive perception of the cessation of an ongoing sound (N(1b)). We propose that N(1b) is distinct from change or mismatch detection and is associated with termination of an ongoing continuous stimulus. We propose to call it the N(egation)-process. SIGNIFICANCE: A constituent of the N(1) complex is shown to be associated with the pre-attentive perception of termination of an ongoing stimulus and to have distinct scalp distribution and intracranial sources.

Attenuation of cerebral oxygen toxicity by sound conditioning.

HYPOTHESIS: Sound conditioning might reduce cerebral oxygen toxicity. BACKGROUND: Cerebral oxygen toxicity is related to high levels of reactive oxygen species. Noise-induced hearing loss has been shown to result from ischemia-reperfusion, in which reactive oxygen species play a major role. Repeated exposure to loud noise at levels below that which produces permanent threshold shift prevented noise-induced hearing loss and was associated with significant elevation of the antioxidant enzymes measured in the inner ear. We tested the hypothesis that sound conditioning might reduce cerebral oxygen toxicity. METHODS: Forty-five guinea pigs were prepared for electroencephalography and auditory brainstem recording. The auditory brainstem recording detection threshold was determined to confirm baseline normal hearing. The animals were divided into three equal groups and subjected to the following procedures: Group 1, electroencephalography electrode implantation and auditory brainstem recording only; Group 2, exposure to oxygen at 608 kPa (the latency to the first electrical discharge in the electroencephalogram preceding the appearance of seizures was measured); and Group 3, sound conditioning followed by oxygen exposure. The animals were killed, and the brains were excised and homogenized. Brain levels of superoxide dismutase, catalase, glutathione peroxidase, glutathione transferase, glutathione reductase, glucose-6-phosphate dehydrogenase, and thiobarbituric acid reactive substances were compared among the groups. RESULTS: Latency to the first electrical discharge was compared between Groups 2 and 3, and was found to be significantly longer in Group 3 (27.9 +/- 11 versus 20.4 +/- 7.6 min, p < 0.03). No significant changes were found in brain levels of superoxide dismutase, catalase, glutathione peroxidase, glutathione transferase, glutathione reductase, glucose-6-phosphate dehydrogenase, or thiobarbituric acid reactive substances. CONCLUSION: Our data show that sound conditioning prolongs the latency to oxygen-induced convulsions. This effect was not accompanied by significant changes in whole-brain antioxidant enzyme activity or the magnitude of lipid peroxidation.

Semantic processing of unattended words and pseudowords in first and second language: an ERP study.

We recorded event related brain potentials to assess stages of linguistic processing of first (L1) and second (L2) language and of pseudowords when subjects were engaged in a different task and did not attend to the words. Young adults (n = 15) were presented with pairs of auditory stimuli consisting of words and pseudowords in L1 and L2 with different voice onset times (VOT), which served as distracters in a short-term memory task. ERPs were recorded from 11 scalp electrodes. The ERP peak amplitudes and latencies were subjected to analysis of variance for the effects of language, meaning and scalp location as well as priming of the second word in the pair by the preceding word. Behavioral results showed that attention was drawn to the primary task and away from the words; yet significant, including semantic, processing was evident in the ERPs to the words, with significant effects of language, meaning and priming. Even with barely any awareness of the stimuli, the brain processes words including distinguishing between L1 and L2 and relating to the stimuli's context.

High-resolution time course of hemispheric dominance revealed by low-resolution electromagnetic tomography.

OBJECTIVE: Auditory event-related brain potentials (ERPs) were recorded during a lexical decision task in response to linguistic and non-linguistic stimuli, to assess the detailed time course of language processing in general, and hemispheric dominance in particular. METHODS: Young adults (n=17) were presented with pairs of auditory stimuli consisting of words, pseudowords and words played backwards in a lexical decision task. ERPs were recorded from 21 scalp electrodes. Current densities were calculated using low-resolution electromagnetic tomography (LORETA). Statistic non-parametric maps of activity were derived from the calculated current densities and the number of active brain voxels in the left and right hemispheres was compared throughout the processing of each stimulus. RESULTS: Our results show that hemispheric dominance is highly time dependent, alternating between the right and left hemispheres at different times, and that the right hemisphere's role in language processing follows a different time course for first and second language. The time course of hemispheric dominance for non-linguistic stimuli was highly variable. CONCLUSIONS: The time course of hemispheric dominance is dynamic, alternating between left and right homologous regions, with different time courses for different stimulus classes.

Evoked potentials to auditory movement sensation in duplex perception.

OBJECTIVE: The purpose of this study was to examine the processing of auditory movement sensation accompanying duplex perception in binaural hearing. 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 vowel-consonant-vowel (V-C-V) sequences /aga/ and /ada/. An illusion of auditory movement (duplex sensation) accompanied the fusion of these V-C-V sequences when the spatial locations of the formant transitions and base were different. 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 processing of auditory movement was studied by a factorial design (ANOVA) and statistical non-parametric mapping (SnPM) of low resolution electromagnetic tomography (LORETA) images of the net-fusion response. Brain regions implicated in auditory movement processing were expected to be associated with the lateralized formant location, which gave rise to duplex perception. In addition, the time-course of significant activation in brain areas that differentiated between fusion conditions was determined. RESULTS: The posterior parietal, anterior cingulate and premotor cortices were found to be implicated in duplex processing. Auditory cortex involvement was also evident, and together with the latter two brain regions was affected by right-ear advantage. CONCLUSIONS: Duplex perception resulting from fusion of spatially separate sounds forming an auditory object results in activation of a network of brain regions reflecting enhanced allocation of attention and the effect of language processing.