Mismatch negativity and auditory sensory memory evaluation: a new faster paradigm

A new faster paradigm to measure the duration of auditory sensory memory, as indexed by mismatch negativity (MMN) suppression to stimuli presented at increasing inter-stimulus intervals (ISI), is proposed. Trains of three stimuli were delivered at very short ISI (300 ms). The inter-train interval varied according to the memory probe interval (MPI) tested. Trains started randomly with a deviant or standard stimulus (50% each), with their event-related brain potentials subtracted to obtain the MMN. The new paradigm provided MMNs identical to the conventional one at MPIs of 0.4 and 4.0 s in young subjects, and revealed MMN suppression when the MPI was increased to 5.0 s in older subjects. The new paradigm estimates auditory sensory memory duration in one-third the time of conventional MMN.     

An event-related potential study of age-related changes in sensitivity to stimulus deviance

The mismatch negativity (MMN) of the event-related (brain) potential (ERP) has been shown to reflect the storage of information in sensory memory and is thought to reflect the operation of a mechanism that compares frequently occurring standard with infrequently occurring deviant acoustic events. The MMN was recorded from young (mean = 23 years) and elderly (mean = 72 years) adults to small (50 Hz) and large (300 Hz) frequency deviants and to a variety of novel, environmental sounds. At each level of deviance, MMN amplitude was smaller in the ERPs of older relative to younger adults. Young, but not older adults showed robust MMNs at the smallest level of deviance. Moreover, a P3 component was observed in the ERPs of the young to both large tonal and novel deviants, whereas a robust P3 component was evident only to the novel deviants in the ERPs of the old. The data suggest that older adults demonstrate less sensitivity to stimulus deviance and that only highly deviant events are likely to involuntarily capture their attention.     

Sensitivity to dynamic auditory and visual stimuli predicts nonword reading ability in both dyslexic and normal readers

BACKGROUND: Developmental dyslexia is a specific disorder of reading and spelling that affects 3-9% of school-age children and adults. Contrary to the view that it results solely from deficits in processes specific to linguistic analysis, current research has shown that deficits in more basic auditory or visual skills may contribute to the reading difficulties of dyslexic individuals. These might also have a crucial role in the development of normal reading skills. Evidence for visual deficits in dyslexia is usually found only with dynamic and not static stimuli, implicating the magnocellular pathway or dorsal visual stream as the cellular locus responsible. Studies of such a dissociation between the processing of dynamic and static auditory stimuli have not been reported previously. RESULTS: We show that dyslexic individuals are less sensitive both to particular rates of auditory frequency modulation (2 Hz and 40 Hz but not 240 Hz) and to dynamic visual-motion stimuli. There were high correlations, for both dyslexic and normal readers, between their sensitivity to the dynamic auditory and visual stimuli. Nonword reading, a measure of phonological awareness believed crucial to reading development, was also found to be related to these sensory measures. CONCLUSIONS: These results further implicate neuronal mechanisms that are specialised for detecting stimulus timing and change as being dysfunctional in many dyslexic individuals. The dissociation observed in the performance of dyslexic individuals on different auditory tasks suggests a sub-modality division similar to that already described in the visual system. These dynamic tests may provide a non-linguistic means of identifying children at risk of reading failure.     

Vibration-induced auditory-cortex activation in a congenitally deaf adult

Considerable changes take place in the number of cerebral neurons, synapses and axons during development, mainly as a result of competition between different neural activities [1-4]. Studies using animals suggest that when input from one sensory modality is deprived early in development, the affected neural structures have the potential to mediate functions for the remaining modalities [5-8]. We now show that similar potential exists in the human auditory system: vibrotactile stimuli, applied on the palm and fingers of a congenitally deaf adult, activated his auditory cortices. The recorded magnetoencephalographic (MEG) signals also indicated that the auditory cortices were able to discriminate between the applied 180 Hz and 250 Hz vibration frequencies. Our findings suggest that human cortical areas, normally subserving hearing, may process vibrotactile information in the congenitally deaf.     

The frequency of two-base tracts in eukaryotic genomes

The mismatch negativity event-related potential (MMN) was elicited in normal school-age children in response to just perceptibly different variants of the speech phoneme /da/. A significant MMN was measured in each subject tested. Child and adult MMNs were similar with respect to peak latency and duration. Measures of MMN magnitude (peak-to-peak amplitude and area) were significantly larger in children than in adults. The results of the present study indicate that the MMN can be elicited in response to minimal acoustic stimulus differences in complex speech signals in school-age children. The results support the feasibility of using the MMN as a tool in the study of deficient auditory perception in children.     

Processing of auditory stimuli during auditory and visual attention as revealed by event-related potentials

Auditory event-related brain potentials (ERPs) were recorded during auditory and visual selective attention tasks. Auditory stimuli consisted of frequent standard tones (1000 Hz) and infrequent deviant tones (1050 Hz and 1300 Hz) delivered randomly to the left and right ears. Visual stimuli were vertical line gratings randomly presented on a video monitor at mean intervals of 6 s. During auditory attention, the subject attended to the stimuli in a designated ear and responded to the 1300-Hz deviants occurring among the attended tones. During visual attention, the subject responded to the occasional visual stimuli. ERPs for tones delivered to the attended ear were negatively displaced relative to ERPs elicited by tones delivered to the unattended ear and to ERPs elicited by auditory stimuli during visual attention. This attention effect consisted of negative difference waves with early and late components. Mismatch negativities (MMNs) were elicited by 1300-Hz and 1050-Hz deviants irrespective of whether they occurred among attended or unattended tones. MMN amplitudes were unaffected by attention, supporting the proposal that the MMN is generated by an automatic cerebral discrimination process.     

Perceptual grouping by infants and preschool children.

We tested infants 6 to 8 months and children 5? years of age for their discrimination of silent intervals between elements of auditory patterns. Standard patterns consisted of six 200-ms tones, three at 440 Hz and three at 659 Hz, with 200-ms intertone intervals (XXXOOO). Contrasting patterns differed only in the addition of a silent increment following the third tone (i.e., between tone groups, XXXOOO) or following the fourth tone (i.e., within a tone group, XXXOOO). Contrasting stimuli presented to infants had increments of 200, 125, 100, or 75 ms; those presented to children had increments of 100, 75, and 50 ms. Infants detected all increments in all locations except the 75-ms increment in the between-group location, but there were no differences in performance for different increment locations. Children detected all increments, but performed significantly worse for between-group increments than for within-group increments. Thus, the context of a temporal increment influences its detectability for children, as it does for adults, indicating that children group the elements of auditory stimuli on the basis of frequency. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Focal stimulation of the thalamic reticular nucleus induces focal gamma waves in cortex

Electrical stimulation of the thalamic reticular nucleus (TRN; 0.5-s trains of 500-Hz 0.5-ms pulses at 5-10 microA) evokes focal oscillations of cortical electrical potentials in the gamma frequency band ( approximately 35-55 Hz). These evoked oscillations are specific to either the somatosensory or auditory cortex and to subregions of the cortical receptotopic map, depending on what part of the TRN is stimulated. Focal stimulation of the internal capsule, however, evokes focal slow potentials, without gamma activity. Our results suggest that the TRN's role extends beyond that of general cortical arousal to include specific modality and submodality activation of the forebrain.     

Low-level steady-state auditory evoked potentials: effects of rate and sedation on detectability

Steady-state auditory evoked potentials (SSAEPs) in alert adults are most detectable at stimulus or modulation rates of about 40 Hz. Sedation reduces the detectability of 40-Hz SSAEPs and increases it for higher rate SSAEPs. This study examined whether rates higher than 40 Hz would be preferable for detecting responses to low-intensity tones in sedated adults. Fourteen normal adults listened to 640-Hz tones at modulation rates (and toneburst rates) of 20-160 Hz, in 10-Hz steps, at levels of 38 and 58 dB peak equivalent sound-pressure level (peSPL) (20 and 40 dB normal hearing level (nHL) for amplitude-modulated (AM) tones), both alert and sedated (1-2 g chloral hydrate). Sedation reduced both signal (SSAEP) power and noise power at all rates, but noise power reduction was greater for higher rates. Detectability in the alert condition was always greatest at 40 Hz. Under sedation, a second detectability peak was present at 90 Hz for 58-dB peSPL tones, approximately equal to that seen at 40 Hz. At 38 dB peSPL (sedated), peak detectability moved from 40 to 50 Hz. These results suggest that presentation/modulation rates around 40 Hz may be optimal for SSAEP detectability at low levels in adults, whether alert or sedated.     

The automated prediction of hearing thresholds in sleeping subjects using auditory steady-state evoked potentials

OBJECTIVE: To examine the relationship between auditory steady-state evoked potentials (SSEPs) and behavioral thresholds in sleeping subjects. DESIGN: 60 adults and children with hearing thresholds ranging from normal to profound were selected on the basis of appropriate audiograms. Behavioral audiograms were determined at the octave frequencies 250-4000 Hz. These behavioral thresholds were then compared with the SSEP thresholds obtained during natural sleep for adults, or natural or sedated sleep for children. RESULTS: A strong relationship between behavioral and SSEP thresholds was observed. The strength of the relationship increased with increasing frequency and increasing degree of the loss. On the basis of these data, the prediction of behavioral thresholds from SSEP levels was determined. It was found that the standard deviation of the error in this prediction decreased with increasing frequency and increasing degree of the loss. There was no significant age effect in the results obtained at any of the frequencies. CONCLUSION: The results suggest the SSEP technique can be used as a predictor of behavioral threshold in adults and children at the frequencies 250-4000 Hz.     

Reduction in excitability of the auditory nerve following electrical stimulation at high stimulus rates. II. Comparison of fixed amplitude with amplitude modulated stimuli

We have previously shown that acute electrical stimulation of the auditory nerve using charge-balanced biphasic current pulses presented continuously can lead to a prolonged decrement in auditory nerve excitability (Tykocinski et al., Hear. Res. 88 (1995), 124-142). This work also demonstrated a reduction in electrically evoked auditory brainstem response (EABR) amplitude decrement when using an otherwise equivalent pulse train with a 50% duty cycle. In the present study we have extended this work in order to compare the effects of electrical stimulation using both fixed amplitude electrical pulse trains and amplitude modulated (AM) pulse trains that more accurately model the dynamic stimulus paradigms used in cochlear implants. EABRs were recorded from guinea pigs following acute stimulation using AM trains of charge-balanced biphasic current pulses. The extent of stimulus-induced reductions in the EABR were compared with our previous results using either fixed amplitude continuous, or 50% duty cycle pulse trains operating at 0.34 microC/phase (2 mA, 170 micros/phase) at 400 or 1000 pulses/s (Tykocinski et al., Hear. Res. 88 (1995) 124-142). The AM pulse train, operating at the same rates, was based on a 1-s sequence of the most extensively activated electrode of a Nucleus Mini-22 cochlear implant using the SPEAK speech processing strategy exposed to 4-talker babble, and delivered the same total charge as the fixed amplitude 50% duty cycle pulse train. Two hours of continuous stimulation induced a significant, rate-dependent reduction in auditory nerve excitability, and showed only a slight post-stimulus recovery for monitoring periods of up to 6 hours. Following 2 or 4 h of stimulation using an otherwise equivalent pulse train with a 50% duty cycle or the AM pulse train, significantly less reduction in the EABR was observed, and recovery to pre-stimulus levels was generally rapid and complete. These differences in the extent of the recovery between the continuous waveform and both the 50% duty cycle and AM waveforms were statistically significant for both 400 and 1000 pulses/s stimuli. Consistent with our previous results, the stimulus changes observed using AM pulse trains were rate dependent, with higher rate stimuli evoking more extensive stimulus-induced changes. The present findings show that while stimulus-induced reductions in neural excitability are dependent on the extent of stimulus-induced neuronal activity, the use of an AM stimulus paradigm further reduces post-stimulus neural fatigue.     

Dynamical cell assemblies in the rat auditory cortex in a reaction-time task

Simultaneous single unit spike trains were recorded in the auditory cortex of freely moving rats performing a complex cognitive task. The experimental paradigm is based on a two-choice task (Go/Nogo) with a two-component (pitch and location) auditory stimulus lasting 500 ms. We report evidence that firstly functional interactions, measured by cross-correlation analysis, between single units in the auditory cortex are dynamically modified in the period preceding the onset of the auditory stimulation, referred to as the 'waiting period'. We secondly observed that spatio-temporal firing patterns both within, and across cell spike trains also tended to appear in the waiting period, several seconds before the actual stimulus delivery. These patterns indicate a very precise repetition of spike discharges separated by long intervals (up to several hundreds of milliseconds). No consistent changes in mean rate were observed. These results suggest that network activity in the auditory cortex is selectively modified in rate independent ways before the actual sensory stimulation. These modifications may reflect participation of recurrent neuronal networks in processes anticipating the expected sensory input.     

Results of cochlear implantation in patients with severe to profound hearing loss--implications for patient selection

In patients with some residual hearing and minor benefit from conventional hearing aids, the benefits of cochlear implantation have to be weighed carefully against eventual adverse effects. In this study, pre- and post-operative thresholds as well as functional results after cochlear implantation are reported; 17 of 44 implanted adults had residual hearing pre-operatively (mean threshold(250 to 4000 Hz): 106 dB HL) in the implanted ear. Residual hearing in the implanted ear could not, in general, be preserved post-operatively. Seventeen of 44 implanted children had some amount of residual hearing in the implanted ear pre-operatively (implanted ear: 114 dB HL; contralateral ear: 109.9 dB HL; mean thresholds(250 to 4000 Hz))). Contrary to the results in adults, residual hearing in the implanted ear remained statistically unchanged. Hearing in the contralateral ear increased significantly from 109.9 to 101.9 dB HL post-operatively. This increase was mainly attributed to maturation of the central auditory pathway. In adults with residual hearing, the monosyllable word recognition scores increased significantly from 9 per cent pre-operatively to 42 per cent post-operatively. Children with residual hearing tended to perform better on speech-related test material compared to children without prior auditory experience. Cochlear implantation is indicated in adults and children with residual hearing and minor benefit from conventional amplification. The contralateral ear in children should be considered for additional acoustical stimulation.     

Properties of memory for unattended spoken syllables.

Whereas previous studies on memory for unattended speech have inadvertently included acoustic interference, the present study examines memory for unattended syllables during a silent period of 1, 5, or 10 s. The primary task was to read silently (Experiments 1–3) or whisper the reading (Experiment 4). Occasionally, when a light cue occurred, the subject was to recall the most recent spoken syllable, as well as the recent reading material. Memory for both the vowels and consonants of the syllables decreased across 10 s, confirming that auditory memory does decay in the absence of acoustic interference. However, the specific patterns of memory decay for vowels versus consonants depended on task demands, including the allocation of attention and the opportunity for subvocal coding. We suggest an account of performance that includes auditory sensory and phonetic memory codes with different properties, used in combination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Media differences in children's story synopses: Radio and television contrasted.

Evaluated the relative effectiveness of 2 media for conveying narrative information by presenting 44 young children (aged 3–6 yrs) and 44 adults with the same story via either TV or radio. Ss then retold the story to an adult from memory. Media differences were found, with children in the radio condition showing significantly more errors in comprehension and memory than children in the TV condition. Both the inclusion of inaccurate story content and the distortion of actual story characteristics occurred more frequently for the purely aural than for the aural and visual. Although Ss in the radio condition showed greater recall of dialog and sound effects than did Ss in the TV condition, the actual events recalled with dialog or other auditory features tended not to be highly important to the overall theme. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mismatch negativity during attend and ignore conditions in Alzheimer's disease

Mismatch negativities (MMNs) of the event-related potential to deviant tones and environmental sounds were recorded during active and ignore oddball sequences in young and elderly controls and patients with probable Alzheimer's disease (PAD). MMNs were smaller in the PAD waveforms compared to those of the controls, suggesting a degraded sensory memory trace in these subjects; however, under ignore conditions, environmental sounds elicited robust MMNs in the PAD group along with N2b and novelty P3 components in similar fashion to controls. As N2b and P3 are usually elicited by attended stimuli, these data suggest that in the PAD subjects, the highly deviant events involuntarily captured attention, perhaps reflecting the activation of an attentional switching mechanism. Because this passive switching is thought to reflect activation of a mechanism located in the frontal lobes, the data suggest that this putative frontal lobe mechanism is relatively intact in the early stages of the disease.     

Impact of sensory acuity on auditory working memory span in young and older adults.

The impact of sensory acuity, processing speed, and working memory capacity on auditory working memory span (L-span) performance at 5 presentation levels was examined in 80 young adults (18–30 years of age) and 26 older adults (60–82 years of age). Lowering the presentation level of the L-span task had a greater detrimental effect on the older adults than on the younger ones. Furthermore, the relationship between sensory acuity and L-span performance varied as a function of age and presentation level. These results suggest that declining acuity plays an important explanatory role in age-related declines in cognitive abilities. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Temporal integration of sequential auditory events: silent period in sound pattern activates human planum temporale

Temporal integration is a fundamental process that the brain carries out to construct coherent percepts from serial sensory events. This process critically depends on the formation of memory traces reconciling past with present events and is particularly important in the auditory domain where sensory information is received both serially and in parallel. It has been suggested that buffers for transient auditory memory traces reside in the auditory cortex. However, previous studies investigating "echoic memory" did not distinguish between brain response to novel auditory stimulus characteristics on the level of basic sound processing and a higher level involving matching of present with stored information. Here we used functional magnetic resonance imaging in combination with a regular pattern of sounds repeated every 100 ms and deviant interspersed stimuli of 100-ms duration, which were either brief presentations of louder sounds or brief periods of silence, to probe the formation of auditory memory traces. To avoid interaction with scanner noise, the auditory stimulation sequence was implemented into the image acquisition scheme. Compared to increased loudness events, silent periods produced specific neural activation in the right planum temporale and temporoparietal junction. Our findings suggest that this area posterior to the auditory cortex plays a critical role in integrating sequential auditory events and is involved in the formation of short-term auditory memory traces. This function of the planum temporale appears to be fundamental in the segregation of simultaneous sound sources.     

Event-related potentials during memorization of spatial locations in the auditory and visual modalities

Event-related potential (ERP) studies of working memory have used delayed S1-S2 match-to-sample tasks in which S1 is held in memory for comparison with S2. ERP negativities in the S1-S2 interval have been interpreted either in terms of working memory operations, or in terms of general preparatory motor processing. Two experiments (N = 20 each) were carried out to explore the nature of ERP negativities in a visuospatial memory task and in an auditory spatial memory task, respectively. In the experimental condition, subjects had to memorize the location of S1 (S1-memorize) so as to respond whether S2 appeared in the same spatial location (S2-memorize). In the control condition, subjects were requested to ignore S1 (S1-passive), and to respond whether S2 matched or not a target location predetermined at the beginning of the trial block (S2-pressing). Results support the two main conclusions of Martin-Loeches et al. (Electroenceph. clin. Neurophysiol., 1994, 91: 363-373). Firstly, that the encoding into memory of spatial location is associated with an ERP negative wave over the brain areas putatively associated with the processing of sensory information (i.e. right parieto-occipital for the visual task; fronto-central and left temporal areas for the auditory task). Secondly, the P300 does not seem to be an important ERP feature related to spatial location encoding and retaining into memory. Despite the distinct scalp distribution of these memory-related, modality-specific ERP negativities, they also showed a considerable degree of temporal synchronicity across modalities.     

Rapid rate transcranial magnetic stimulation--a safety study

We assessed the safety of repeated short trains (4 stimuli) of rapid-rate transcranial magnetic stimulation (rrTMS) over the left motor cortex in 6 healthy normal subjects. rrTMS involved two separate blocks of 50 consecutive trains of 4 stimuli at a frequency of 20 Hz and an intensity of 5-10% above active motor threshold. We monitored EEG, and assessed aspects of neurological (balance, gait, two-point discrimination, blood pressure, pulse rate), cognitive (attention, memory, executive function) and motor function (speed of movement initiation and execution and manual dexterity) before and after the two blocks of rrTMS. EMG was also recorded from a number of hand, forearm and arm muscles contralateral to the site of stimulation. Two blocks of repeated rrTMS at 20 Hz and 5-10% above active motor threshold did not produce any adverse effects. Measures of neurological, cognitive and motor function showed no change following rrTMS. From the EMG recording there was evidence of increase in the amplitude of the motor evoked potentials (MEPs) recorded from the biceps in one subject during the first block of rrTMS, but this did not occur in the second block. A similar magnification of MEPs was also observed in another subject only during the second block of stimulation. When applied using parameters falling within published guidelines (Pascual-Leone et al., 1993; Pascual-Leone et al., 1994), repeated rrTMS is a relatively safe technique in healthy normal subjects. As rrTMS allows disruption of cortical function for a longer period, it has the potential of becoming a particularly useful tool for the study of cognitive function as well as sensory or motor function.