Age-related change in neural processing of time-dependent stimulus features

Age-related neural changes underlying long-term recognition of musical sequences

Aging is often associated with decline in brain processing power and neural predictive capabilities. To challenge this notion, we used magnetoencephalography (MEG) and magnetic resonance imaging (MRI) to record the whole-brain activity of 39 older adults (over 60 years old) and 37 young adults (aged 18-25 years) during recognition of previously memorised and varied musical sequences. Results reveal that when recognising memorised sequences, the brain of older compared to young adults reshapes its functional organisation. In fact, it shows increased early activity in sensory regions such as the left auditory cortex (100 ms and 250 ms after each note), and only moderate decreased activity (350 ms) in medial temporal lobe and prefrontal regions. When processing the varied sequences, older adults show a marked reduction of the fast-scale functionality (250 ms after each note) of higher-order brain regions including hippocampus, ventromedial prefrontal and inferior temporal cortices, while no differences are observed in the auditory cortex. Accordingly, young outperform older adults in the recognition of novel sequences, while no behavioural differences are observed with regards to memorised ones. Our findings show age-related neural changes in predictive and memory processes, integrating existing theories on compensatory neural mechanisms in non-pathological aging.

Cortical Auditory Evoked Potential Indices of Impaired Sensory Gating in People With Chronic Tinnitus

OBJECTIVES

The primary aim of this study was to evaluate whether there is cortical auditory evoked potential (CAEP) evidence of impaired sensory gating in individuals with tinnitus. On the basis of the proposed mechanism of tinnitus generation, including a thalamocortical inhibitory deficit, it was hypothesized that individuals with tinnitus would lack the normal inhibitory effect on the second CAEP response in a paired-click sensory gating paradigm, resulting in larger sensory gating ratios in individuals with tinnitus relative to age-, sex-, and hearing-matched controls. Further, this study assessed the relative predictive influence of tinnitus presence versus other related individual characteristics (hearing loss, age, noise exposure history, and speech perception in noise) on sensory gating.

DESIGN

A paired-click CAEP paradigm was used to measure sensory gating outcomes in an independent group's experimental design. Adults who perceived chronic unilateral or bilateral tinnitus were matched with control group counterparts without tinnitus by age, hearing, and sex (n = 18; 10 females, eight males in each group). Amplitude, area, and latency sensory gating ratios were determined for measured P1, N1, and P2 responses evoked by the first and second click in the paradigm and compared between groups by independent t tests. The relative influence of tinnitus (presence/absence), age (in years), noise exposure history (subjective self-report), hearing loss (pure-tone audiometric thresholds), and speech perception in noise (signal to noise ratio-50) on sensory gating was determined based on the proportional reduction in error associated with each variable using multiple regression.

RESULTS

A significantly larger was identified in the tinnitus group relative to the control group, consistent with the hypothesis of poorer sensory gating and poorer thalamocortical inhibition in individuals with chronic tinnitus. On the basis of the proportional reduction in error, the influence of tinnitus presence better predicted compared with other related individual characteristics (age, noise exposure history, hearing loss, and speech perception in noise).

CONCLUSIONS

Results consistent with poorer sensory gating, including a larger , were found for the tinnitus group compared with the controls. This finding supported a thalamocortical inhibitory deficit in the tinnitus group and suggests that individuals with tinnitus may have poorer sensory gating. However, the tinnitus group did differ from controls in meaningful ways including having worse pure-tone thresholds in the extended high-frequency region, lower high-frequency distortion product otoacoustic emissions, and poorer speech perception in noise. Although tinnitus best predicted sensory gating outcomes, the specific effects of tinnitus presence versus absence and other individual characteristics on sensory gating cannot be completely separated.

The temporal precision of audiovisual integration is associated with longitudinal fall incidents but not sensorimotor fall risk in older adults

Sustained multisensory integration over long inter-stimulus time delays is typically found in older adults, particularly those with a history of falls. However, the extent to which the temporal precision of audio-visual integration is associated with longitudinal fall or fall risk trajectories is unknown. A large sample of older adults (N = 2319) were grouped into longitudinal trajectories of self-reported fall incidents (i.e., decrease, stable, or increase in number) and, separately, their performance on a standard, objective measure of fall risk, Timed Up and Go (TUG; stable, moderate decline, severe decline). Multisensory integration was measured once as susceptibility to the Sound-Induced Flash Illusion (SIFI) across three stimulus onset asynchronies (SOAs): 70 ms, 150 ms and 230 ms. Older adults with an increasing fall number showed a significantly different pattern of performance on the SIFI than non-fallers, depending on age: For adults with increasing incidents of falls, those aged 53-59 years showed a much smaller difference in illusion susceptibility at 70 ms versus 150 ms than those aged 70 + years. In contrast, non-fallers showed a more comparable difference between these SOA conditions across age groups. There was no association between TUG performance trajectories and SIFI susceptibility. These findings suggests that a fall event is associated with distinct temporal patterns of multisensory integration in ageing and have implications for our understanding of the mechanisms underpinning brain health in older age.

Combined Bifrontal Transcranial Direct Current Stimulation and Auditory Stroop Training in Chronic Tinnitus

Patients with tinnitus experience difficulties in cognitive control and executive functions. Many of which are regarded as the cause of tinnitus rather than its complications. Methods for the improvement of inhibitory and cognitive control seem to be effective in the control of tinnitus. In this study, transcranial direct current stimulation and auditory Stroop exercise were have been to improve inhibitory control and the ability to ignore tinnitus in patients suffering from chronic tinnitus. 34 patients with chronic tinnitus (> 6 months) were randomly divided into two groups. The first group consist of 17 patients who received 6 sessions of tDCS followed by 6 sessions of auditory Stroop training. The second group received 6 sessions of sham tDCS followed by 6 sessions of auditory Stroop training. The initial evaluations including pure tone audiometry, psychoacoustic measurements, tinnitus handicap inventory (THI) survey and visual analog scale (VAS) of annoyance and loudness were performed before, immediately after, and one month after the tDCS, sham, and Stroop training. The results of this study revealed a significant reduction in THI score, VAS of loudness, and annoyance of tinnitus. A significant correlation was detected between the reaction time of incongruent words in the Stroop task and improvement of THI score and VAS of annoyance. Combined tDCS and Stroop training efficiently improve chronic tinnitus.

Testing A Hypothesis: Tinnitus Control by Enhancing Physiological Inhibition

Background

Deficit in cognitive functions and central executive function is one of the popular hypotheses on the underlying cause of tinnitus. Some studies expressed the effect of tinnitus on the inhibitory cognitive tasks, referring to the slower inhibitory results such as in the Stroop task in the people suffering from tinnitus as compared to normal subjects. Since Stroop engages the network overlapping the attention and tinnitus distress networks, it seems likely that Stroop exercises can effectively contribute to controlling the tinnitus and its consequent distress through improvement of the cognitive function and increasing the physiological inhibition.

Method

A total of 25 patients with chronic tinnitus (> 6 months) were randomly divided into two groups: an intervention group of 15 patients and a control group of 10 patients. Both groups were subjected to initial evaluations including pure tone audiometry, psychoacoustic measurements, tinnitus handicap inventory (THI) survey, and visual analogue scale (VAS) of annoyance and loudness. The intervention group underwent a rehabilitation program consisting of 6 Stroop training sessions. The control group didn't receive any training. Afterwards, both groups were reevaluated and the results were compared to those of initial evaluations.

Results

Results of this study indicated significant differences in THI scores and VAS of annoyance, before and after Stroop training in the intervention group, although no significant difference was observed when it came to VAS of loudness.

Conclusion

Successive sessions of conflict processing training can improve the annoyance of tinnitus by enhancing the patient's inhibition control, making this task a safe practice for tinnitus treatment.

Auditory steady state responses elicited by silent gaps embedded within a broadband noise

Background

Auditory temporal processing plays an important role in speech comprehension. Usually, behavioral tests that require subjects to detect silent gaps embedded within a continuous sound are used to assess the ability of auditory temporal processing in humans. To evaluate auditory temporal processing objectively, the present study aimed to measure the auditory steady state responses (ASSRs) elicited by silent gaps of different lengths embedded within a broadband noise. We presented a broadband noise with 40-Hz silent gaps of 3.125, 6.25, and 12.5 ms.

Results

The 40-Hz silent gaps of 3.125, 6.25, and 12.5 ms elicited clear ASSRs. Longer silent gaps elicited larger ASSR amplitudes and ASSR phases significantly differed between conditions.

Conclusion

The 40 Hz gap-evoked ASSR contributes to our understanding of the neural mechanisms underlying auditory temporal processing and may lead to the development of objective measures of auditory temporal acuity in humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-022-00712-0.

Prediction in the aging brain: Merging cognitive, neurological, and evolutionary perspectives

Although the aging brain is typically characterized by declines in a variety of cognitive functions, there has been growing attention to cognitive functions that may stabilize or improve with age. We integrate evidence from behavioral, computational, and neurological domains under the hypothesis that over the life span the brain becomes more effective at predicting (i.e., utilizing knowledge) compared to learning. Moving beyond mere description of the empirical literature—with the aim of arriving at a deeper understanding of cognitive aging—we provide potential explanations for a learning-to-prediction shift based on evolutionary models and principles of senescence and plasticity. The proposed explanations explore whether the occurrence of a learning-to-prediction shift can be explained by (changes in) the fitness effects of learning and prediction over the life span. Prediction may optimize (a) the allocation of limited resources across the life span, and/or (b) late-life knowledge transfer (social learning). Alternatively, late-life prediction may reflect a slower decline in prediction compared to learning. By discussing these hypotheses, we aim to provide a foundation for an integrative neurocognitive–evolutionary perspective on aging and to stimulate further theoretical and empirical work.

The mismatch negativity responses of individuals with tinnitus with normal extended high-frequency hearing-is it possible to use mismatch negativity in the evaluation of tinnitus?

OBJECTIVE

This study uses the multi-feature paradigm to compare the MMN responses of individuals with normal hearing thresholds, including the high frequencies with and without tinnitus.

METHODS

Sixteen subjects with chronic subjective idiopathic tinnitus and twenty matched healthy controls were included in the study. Participants with hearing thresholds (0.125-16 kHz) less than 20 dB HL and MoCA test scores above 21 were included in the study. MMN responses and topographical maps of the responses resulting from the multi-feature MMN paradigm were recorded from 22 surface scalp electrodes. Amplitude and latency parameters of the MMN responses of five different deviants, consisting of frequency, intensity, duration, location, and silent gap, were compared between the two groups.

RESULTS

The amplitudes of MMN responses were lower in the tinnitus group than in the control group at Fz electrode for all deviant types. At the same time, there was no difference between the groups for MMN latencies and, no correlation was found between THI and MMN.

CONCLUSION

According to our results, the MMN might indicate a possible impairment in pre-attentive and automatic central auditory processing for chronic tinnitus patients. Since MMN responses in the tinnitus group differ from those of healthy individuals, it might be used as a reference for evaluating the central auditory pathways of tinnitus patients.

Neural correlates of auditory sensory memory dynamics in the aging brain

The auditory system allows us to monitor background environmental sound patterns and recognize deviations that may indicate opportunities or threats. The mismatch negativity and P3a potentials have generators in the auditory and inferior frontal cortex and index expected sound patterns (standards) and any aberrations (deviants). The mismatch negativity and P3a waveforms show increased positivity for consecutive standards and deviants preceded by more standards. We hypothesized attenuated repetition effects in older participants, potentially because of differences in prefrontal functions. Young (23 ± 5 years) and older (75 ± 5 years) adults were tested in 2 oddball paradigms with pitch or location deviants. Significant repetition effects were observed in the young standard and deviant waveforms at multiple time windows. Except the earliest time window (30-100 ms), repetition effects were absent in the older group. Repetition effects were significant at frontal but not temporal lobe sites and did not differ among pitch and location deviants. However, P3a repetition was evident in both ages. Findings suggest age differences in the dynamic updating of sensory memory for background sound patterns.

Inhibitory Control Impairment on Somatosensory Gating Due to Aging: An Event-Related Potential Study

The capacity to suppress irrelevant incoming input, termed sensory gating, is one of the most investigated inhibitory processes associated with cognitive impairments due to aging. The aim of this study was to examine the influence of aging on sensory gating by using somatosensory event-related potentials (ERPs) elicited by repetitive non-painful tactile stimulation (paired-pulsed task). Somatosensory ERPs were recorded in 20 healthy young adults and 20 healthy older adults while they received two identical pneumatic stimuli (S1 and S2) of 100 ms duration with an inter-stimulus interval of 550 ± 50 ms on both forefingers. The difference between the somatosensory ERPs amplitude elicited by S1 and S2 was computed as a sensory gating measure. The amplitude and the latency of P50, N100 and late positive complex (LPC) were analyzed as well as the source generators of the gating effect. Reduced sensory gating was found in older individuals for N100 at frontal and centro-parietal electrodes and for LPC at fronto-central electrodes. Source localization analyses also revealed a reduced current density during gating effect in the older group in frontal areas in N100 and LPC. Moreover, older individuals showed delayed latencies in N100. No significant gating effect differences were found between groups in P50. These findings suggest an age-related slowing of processing speed and a reduced efficiency of inhibitory mechanisms in response to repetitive somatosensory information during stimulus evaluation, and a preservation of processing speed and inhibitory control during early stimulus coding in aging.

Automatic auditory and somatosensory brain responses in relation to cognitive abilities and physical fitness in older adults

In normal ageing, structural and functional changes in the brain lead to an altered processing of sensory stimuli and to changes in cognitive functions. The link between changes in sensory processing and cognition is not well understood, but physical fitness is suggested to be beneficial for both. We recorded event-related potentials to somatosensory and auditory stimuli in a passive change detection paradigm from 81 older and 38 young women and investigated their associations with cognitive performance. In older adults also associations to physical fitness were studied. The somatosensory mismatch response was attenuated in older adults and it associated with executive functions. Somatosensory P3a did not show group differences, but in older adults, it associated with physical fitness. Auditory N1 and P2 responses to repetitive stimuli were larger in amplitude in older than in young adults. There were no group differences in the auditory mismatch negativity, but it associated with working memory capacity in young but not in older adults. Our results indicate that in ageing, changes in stimulus encoding and deviance detection are observable in electrophysiological responses to task-irrelevant somatosensory and auditory stimuli, and the higher somatosensory response amplitudes are associated with better executive functions and physical fitness.

Spectral Entropy Can Predict Changes of Working Memory Performance Reduced by Short-Time Training in the Delayed-Match-to-Sample Task

Spectral entropy, which was generated by applying the Shannon entropy concept to the power distribution of the Fourier-transformed electroencephalograph (EEG), was utilized to measure the uniformity of power spectral density underlying EEG when subjects performed the working memory tasks twice, i.e., before and after training. According to Signed Residual Time (SRT) scores based on response speed and accuracy trade-off, 20 subjects were divided into two groups, namely high-performance and low-performance groups, to undertake working memory (WM) tasks. We found that spectral entropy derived from the retention period of WM on channel FC4 exhibited a high correlation with SRT scores. To this end, spectral entropy was used in support vector machine classifier with linear kernel to differentiate these two groups. Receiver operating characteristics analysis and leave-one out cross-validation (LOOCV) demonstrated that the averaged classification accuracy (CA) was 90.0 and 92.5% for intra-session and inter-session, respectively, indicating that spectral entropy could be used to distinguish these two different WM performance groups successfully. Furthermore, the support vector regression prediction model with radial basis function kernel and the root-mean-square error of prediction revealed that spectral entropy could be utilized to predict SRT scores on individual WM performance. After testing the changes in SRT scores and spectral entropy for each subject by short-time training, we found that 16 in 20 subjects’ SRT scores were clearly promoted after training and 15 in 20 subjects’ SRT scores showed consistent changes with spectral entropy before and after training. The findings revealed that spectral entropy could be a promising indicator to predict individual’s WM changes by training and further provide a novel application about WM for brain–computer interfaces.

Electrophysiological Indicators of the Age-Related Deterioration in the Sensitivity to Auditory Duration Deviance

The present study investigates age-related changes in duration discrimination in millisecond time domain. We tested young (N = 20, mean age = 24.5, SD = 2.97) and elderly (N = 20, mean age = 65.2, SD = 2.94) subjects using the mismatch negativity (MMN) paradigm. White-noise bursts of two different durations (50 and 10 ms) were presented in two oddball blocks. In one block (Increment Condition), the repetitive sequence of 10 ms standards was interspersed by occasional 50 ms deviants. In the Decrement Condition, the roles of the two stimuli were reversed. We analyzed the P1-N1 complex, MMN and P3a and found the effect of age for all these components. Moreover, the impact of stimulus presentation condition (increment/decrement) was observed for MMN and P3a. Our results confirmed the previous evidence for deteriorated duration discrimination in elderly people. Additionally, we found that this effect may be influenced by procedural factors.

The role of temporal structure in the investigation of sensory memory, auditory scene analysis, and speech perception: a healthy-aging perspective

Listening situations with multiple talkers or background noise are common in everyday communication and are particularly demanding for older adults. Here we review current research on auditory perception in aging individuals in order to gain insights into the challenges of listening under noisy conditions. Informationally rich temporal structure in auditory signals--over a range of time scales from milliseconds to seconds--renders temporal processing central to perception in the auditory domain. We discuss the role of temporal structure in auditory processing, in particular from a perspective relevant for hearing in background noise, and focusing on sensory memory, auditory scene analysis, and speech perception. Interestingly, these auditory processes, usually studied in an independent manner, show considerable overlap of processing time scales, even though each has its own 'privileged' temporal regimes. By integrating perspectives on temporal structure processing in these three areas of investigation, we aim to highlight similarities typically not recognized.

Somatosensory mismatch response in young and elderly adults

Aging is associated with cognitive decline and alterations in early perceptual processes. Studies in the auditory and visual sensory modalities have shown that the mismatch negativity [or the mismatch response (MMR)], an event-related potential (ERP) elicited by a deviant stimulus in a background of homogenous events, diminishes with aging and cognitive decline. However, the effects of aging on the somatosensory MMR (sMMR) are not known. In the current study, we recorded ERPs to electrical pulses to different fingers of the left hand in a passive oddball experiment in young (22–36 years) and elderly (66–95 years) adults engaged in a visual task. The MMR was found to deviants as compared to standards at two latency ranges: 180–220 ms and 250–290 ms post-stimulus onset. At 180–220 ms, within the young, the MMR was found at medial electrode sites, whereas aged did not show any amplitude difference between the stimulus types at the same latency range. At 250–290 ms, the MMR was evident with attenuated amplitude and narrowed scalp distribution among aged (Fz) compared to young (fronto-centrally and lateral parietal sites). Hence, the results reveal that the somatosensory change detection mechanism is altered in aging. The sMMR can be used as a reliable measure of age-related changes in sensory-cognitive functions.

Mismatch negativity (MMN) as an index of cognitive dysfunction

Cognition is often affected in a variety of neuropsychiatric, neurological, and neurodevelopmental disorders. The neural discriminative response, reflected in mismatch negativity (MMN) and its magnetoencephalographic equivalent (MMNm), has been used as a tool to study a variety of disorders involving auditory cognition. MMN/MMNm is an involuntary brain response to auditory change or, more generally, to pattern regularity violation. For a number of disorders, MMN/MMNm amplitude to sound deviance has been shown to be attenuated or the peak-latency of the component prolonged compared to controls. This general finding suggests that while not serving as a specific marker to any particular disorder, MMN may be useful for understanding factors of cognition in various disorders, and has potential to serve as an indicator of risk. This review presents a brief history of the MMN, followed by a description of how MMN has been used to index auditory processing capability in a range of neuropsychiatric, neurological, and neurodevelopmental disorders. Finally, we suggest future directions for research to further enhance our understanding of the neural substrate of deviance detection that could lead to improvements in the use of MMN as a clinical tool.

Auditory post-processing in a passive listening task is deficient in Alzheimer's disease

OBJECTIVE

To investigate whether automatic auditory post-processing is deficient in patients with Alzheimer's disease and is related to sensory gating.

METHODS

Event-related potentials were recorded during a passive listening task to examine the automatic transient storage of auditory information (short click pairs). Patients with Alzheimer's disease were compared to a healthy age-matched control group. A young healthy control group was included to assess effects of physiological aging.

RESULTS

A bilateral frontal negativity in combination with deep temporal positivity occurring 500 ms after stimulus offset was reduced in patients with Alzheimer's disease, but was unaffected by physiological aging. Its amplitude correlated with short-term memory capacity, but was independent of sensory gating in healthy elderly controls. Source analysis revealed a dipole pair in the anterior temporal lobes.

CONCLUSION

Results suggest that auditory post-processing is deficient in Alzheimer's disease, but is not typically related to sensory gating. The deficit could neither be explained by physiological aging nor by problems in earlier stages of auditory perception. Correlations with short-term memory capacity and executive control tasks suggested an association with memory encoding and/or overall cognitive control deficits.

SIGNIFICANCE

An auditory late negative wave could represent a marker of auditory working memory encoding deficits in Alzheimer's disease.

Neurophysiological investigation of phonological input: aging effects and development of normative data

The current study investigated attended and unattended auditory phoneme discrimination using the P300 and Mismatch Negativity event-related potentials (ERPs). Three phonemic contrasts present in the Dutch language were compared. Additionally, auditory word recognition was investigated by presenting rare pseudowords among frequent words. Two main goals were: (1) obtain normative data for ERP latencies (ms) and amplitudes (μV) and (2) examine aging influences. Seventy-one healthy subjects (21-83 years) were included. During phoneme discrimination aging was associated with increased latencies and decreased amplitudes. However, a discrepancy between attended and unattended processing, as well as between phonemic contrasts, was found. During word recognition aging only had an impact on ERPs elicited by real words, indicating that mainly semantic processes were altered leaving lexical processes unharmed. Early sensory-perceptual processes, reflected by N100 and P50, were free from aging influences. In future, neurophysiological normative data can be applied in the evaluation of acquired language disorders.

Effects of aging on neuromagnetic mismatch responses to pitch changes

Although aging-related alterations in the auditory sensory memory and involuntary change discrimination have been widely studied, it remains controversial whether the mismatch negativity (MMN) or its magnetic counterpart (MMNm) is modulated by physiological aging. This study aimed to examine the effects of aging on mismatch activity to pitch deviants by using a whole-head magnetoencephalography (MEG) together with distributed source modeling analysis. The neuromagnetic responses to oddball paradigms consisting of standards (1000 Hz, p=0.85) and deviants (1100 Hz, p=0.15) were recorded in healthy young (n=20) and aged (n=18) male adults. We used minimum norm estimate of source reconstruction to characterize the spatiotemporal neural dynamics of MMNm responses. Distributed activations to MMNm were identified in the bilateral fronto-temporo-parietal areas. Compared to younger participants, the elderly exhibited a significant reduction of cortical activation in bilateral superior temporal guri, superior temporal sulci, inferior fontal gyri, orbitofrontal cortices and right inferior parietal lobules. In conclusion, our results suggest an aging-related decline in auditory sensory memory and automatic change detection as indexed by MMNm.

Cholinergic modulation of auditory processing, sensory gating and novelty detection in human participants

RATIONALE

Suppression of redundant auditory information and facilitation of deviant, novel, or salient sounds can be assessed with paired-click and oddball tasks, respectively. Electrophysiological correlates of perturbed auditory processing found in these paradigms are likely to be a trait marker or candidate endophenotype for schizophrenia.

OBJECTIVE

This is the first study to investigate the effects of the muscarinic M1 antagonist biperiden and the cholinesterase inhibitor rivastigmine on auditory-evoked potentials (AEPs), sensory gating, and mismatch negativity (MMN) in young, healthy volunteers.

RESULTS

Biperiden increased P50 amplitude and prolonged N100 and P200 latency in the paired-click task but did not affect sensory gating. Rivastigmine was able to reverse the effects of biperiden on N100 and P200 latency. Biperiden increased P50 latency in the novelty oddball task, which was reversed by concurrent administration of rivastigmine. Rivastigmine shortened N100 latency and enhanced P3a amplitude in the novelty oddball paradigm, both of which were reversed by biperiden.

CONCLUSION

The muscarinic M1 receptor appears to be involved in preattentive processing of auditory information in the paired-click task. Additional effects of biperiden versus rivastigmine were reversed by a combination treatment, which renders attribution of these findings to muscarinic M1 versus muscarinic M2-M5 or nicotinic receptors much more difficult. It remains to be seen whether the effects of cholinergic drugs on AEPs are specifically related to the abnormalities found in schizophrenia. Alternatively, aberrant auditory processing could also be indicative of a general disturbance in neural functioning shared by several neuropsychiatric disorders and/or neurodegenerative changes seen in aging.

Aging effects on functional auditory and visual processing using fMRI with variable sensory loading

INTRODUCTION

Traditionally, studies investigating the functional implications of age-related structural brain alterations have focused on higher cognitive processes; by increasing stimulus load, these studies assess behavioral and neurophysiological performance. In order to understand age-related changes in these higher cognitive processes, it is crucial to examine changes in visual and auditory processes that are the gateways to higher cognitive functions. This study provides evidence for age-related functional decline in visual and auditory processing, and regional alterations in functional brain processing, using non-invasive neuroimaging.

METHODS

Using functional magnetic resonance imaging (fMRI), younger (n=11; mean age=31) and older (n=10; mean age=68) adults were imaged while observing flashing checkerboard images (passive visual stimuli) and hearing word lists (passive auditory stimuli) across varying stimuli presentation rates.

RESULTS

Younger adults showed greater overall levels of temporal and occipital cortical activation than older adults for both auditory and visual stimuli. The relative change in activity as a function of stimulus presentation rate showed differences between young and older participants. In visual cortex, the older group showed a decrease in fMRI blood oxygen level dependent (BOLD) signal magnitude as stimulus frequency increased, whereas the younger group showed a linear increase. In auditory cortex, the younger group showed a relative increase as a function of word presentation rate, while older participants showed a relatively stable magnitude of fMRI BOLD response across all rates. When analyzing participants across all ages, only the auditory cortical activation showed a continuous, monotonically decreasing BOLD signal magnitude as a function of age.

CONCLUSIONS

Our preliminary findings show an age-related decline in demand-related, passive early sensory processing. As stimulus demand increases, visual and auditory cortex do not show increases in activity in older compared to younger people. This may negatively impact on the fidelity of information available to higher cognitive processing. Such evidence may inform future studies focused on cognitive decline in aging.

Differentiation of schizophrenia patients from healthy subjects by mismatch negativity and neuropsychological tests

BACKGROUND

Schizophrenia is a heterogeneous disorder with diverse presentations. The current and the proposed DSM-V diagnostic system remains phenomenologically based, despite the fact that several neurobiological and neuropsychological markers have been identified. A multivariate approach has better diagnostic utility than a single marker method. In this study, the mismatch negativity (MMN) deficit of schizophrenia was first replicated in a Han Chinese population, and then the MMN was combined with several neuropsychological measurements to differentiate schizophrenia patients from healthy subjects.

METHODOLOGY/PRINCIPAL FINDINGS

120 schizophrenia patients and 76 healthy controls were recruited. Each subject received examinations for duration MMN, Continuous Performance Test, Wisconsin Card Sorting Test, and Wechsler Adult Intelligence Scale Third Edition (WAIS-III). The MMN was compared between cases and controls, and important covariates were investigated. Schizophrenia patients had significantly reduced MMN amplitudes, and MMN decreased with increasing age in both patient and control groups. None of the neuropsychological indices correlated with MMN. Predictive multivariate logistic regression models using the MMN and neuropsychological measurements as predictors were developed. Four predictors, including MMN at electrode FCz and three scores from the WAIS-III (Arithmetic, Block Design, and Performance IQ) were retained in the final predictive model. The model performed well in differentiating patients from healthy subjects (percentage of concordant pairs: 90.5%).

CONCLUSIONS/SIGNIFICANCE

MMN deficits were found in Han Chinese schizophrenia patients. The multivariate approach combining biomarkers from different modalities such as electrophysiology and neuropsychology had a better diagnostic utility.

The mismatch negativity (MMN)--a unique window to disturbed central auditory processing in ageing and different clinical conditions

In this article, we review clinical research using the mismatch negativity (MMN), a change-detection response of the brain elicited even in the absence of attention or behavioural task. In these studies, the MMN was usually elicited by employing occasional frequency, duration or speech-sound changes in repetitive background stimulation while the patient was reading or watching videos. It was found that in a large number of different neuropsychiatric, neurological and neurodevelopmental disorders, as well as in normal ageing, the MMN amplitude was attenuated and peak latency prolonged. Besides indexing decreased discrimination accuracy, these effects may also reflect, depending on the specific stimulus paradigm used, decreased sensory-memory duration, abnormal perception or attention control or, most importantly, cognitive decline. In fact, MMN deficiency appears to index cognitive decline irrespective of the specific symptomatologies and aetiologies of the different disorders involved.

Electrophysiological evidence for age effects on sensory memory processing of tonal patterns

In older adults, difficulties processing complex auditory scenes, such as speech comprehension in noisy environments, might be due to a specific impairment of temporal processing at early, automatic processing stages involving auditory sensory memory (ASM). Even though age effects on auditory temporal processing have been well-documented, there is a paucity of research on how ASM processing of more complex tone-patterns is altered by age. In the current study, age effects on ASM processing of temporal and frequency aspects of two-tone patterns were investigated using a passive listening protocol. The P1 component, the mismatch negativity (MMN) and the P3a component of event-related brain potentials (ERPs) to tone frequency and temporal pattern deviants were recorded in younger and older adults as a measure of auditory event detection, ASM processing, and attention switching, respectively. MMN was elicited with smaller amplitude to both frequency and temporal deviants in older adults. Furthermore, P3a was elicited only in the younger adults. In conclusion, the smaller MMN amplitude indicates that automatic processing of both frequency and temporal aspects of two-tone patterns is impaired in older adults. The failure to initiate an attention switch, suggested by the absence of P3a, indicates that impaired ASM processing of patterns may lead to less distractibility in older adults. Our results suggest age-related changes in ASM processing of patterns that cannot be explained by an inhibitory deficit.

Neurophysiologic markers of abnormal brain activity in schizophrenia

Cortical electrophysiologic event-related potentials are multidimensional measures of information processing that are well-suited for efficiently parsing automatic and controlled components of cognition that span the range of deficits evidenced in schizophrenia patients. These information processes are key cognitive measures that are recognized as informative and valid targets for understanding the neurobiology of schizophrenia. These measures may be used in concert with the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) neurocognitive measures in the development of novel treatments for schizophrenia and related neuropsychiatric disorders. The employment of novel event-related potential paradigms designed to carefully characterize the early spectrum of perceptual and cognitive information processing allows investigators to identify the neurophysiologic basis of cognitive dysfunction in schizophrenia and to examine the associated clinical and functional impairments.

The relationship between preattentive sensory processing deficits and age in schizophrenia patients

OBJECTIVE

Auditory mismatch negativity (MMN) and P3a index preattentive detection of rare stimuli. Their amplitudes normally decrease with age. Previous studies have reported generally smaller than normal MMN and P3a in schizophrenia patients. We aimed to further characterize the course of these deficits over schizophrenia patients' lifespan.

METHODS

In 253 schizophrenia patients and 147 normal comparison participants (NCPs) encompassing a wide age range (18-65), event-related potentials were recorded while participants watched a silent video and were presented binaurally with 1-kHz tones 500ms apart, including standards (P=.90, 50-ms duration) and deviants (P=0.10, 100-ms).

RESULTS

Over the entire age range, MMN and P3a were smaller in schizophrenia patients than NCPs. MMN amplitude declined with age in both groups, though slightly less steeply in schizophrenia patients than NCPs. P3a amplitude declined with age in NCPs but not in schizophrenia patients.

CONCLUSIONS

In our cohort of schizophrenia patients, MMN and P3a deficits were already present at the youngest ages. MMN declined further with age, whereas P3a amplitude remained stable.

SIGNIFICANCE

This knowledge about how MMN and P3a amplitudes vary with age in schizophrenia patients compared to NCPs can help improve the utility of these indices as clinical endophenotypes or biomarkers.

Nicotine enhances automatic temporal processing as measured by the mismatch negativity waveform

INTRODUCTION

Cholinergic agonists and, more specifically, nicotine, have been found to enhance a number of cognitive processes. The effect of nicotine on temporal processing is not known. The use of behavioral measures of temporal processing to measure its effect could be confounded by the general effects of nicotine on attention. Mismatch negativity (MMN) has been used as a physiological measure of automatic temporal processing to avoid this potential confound.

METHODS

A total of 20 subjects (11 nonsmokers and 9 smokers following 2 hr of abstinence) participated in a two-visit single-blind, placebo-controlled crossover study of the effect of nicotine on MMN indices in response to an interstimulus interval deviant.

RESULTS

Nicotine-enhanced MMN amplitudes from baseline recording to postdrug recording greater than did the placebo condition. This enhancement was seen in both nonsmokers and smokers. Nicotine had no significant effect on MMN latency or N100 amplitude or latency.

DISCUSSION

This is the first study to demonstrate a nicotine-related enhancement of MMN amplitude to an interstimulus interval duration deviant and confirms our hypothesis that nicotine enhances preattentive temporal processing. Nicotinic agonists may represent a potential therapeutic option for individuals with abnormalities in early sensory or temporal processing related to cholinergic system abnormalities. Methodologically, our paradigm of nicotine administration in abstinent smokers is important because it resulted in both minimal withdrawal symptoms and meaningful data that are not attributable solely to relief of withdrawal.

Auditory temporal processing in healthy aging: a magnetoencephalographic study

BACKGROUND

Impaired speech perception is one of the major sequelae of aging. In addition to peripheral hearing loss, central deficits of auditory processing are supposed to contribute to the deterioration of speech perception in older individuals. To test the hypothesis that auditory temporal processing is compromised in aging, auditory evoked magnetic fields were recorded during stimulation with sequences of 4 rapidly recurring speech sounds in 28 healthy individuals aged 20 - 78 years.

RESULTS

The decrement of the N1m amplitude during rapid auditory stimulation was not significantly different between older and younger adults. The amplitudes of the middle-latency P1m wave and of the long-latency N1m, however, were significantly larger in older than in younger participants.

CONCLUSION

The results of the present study do not provide evidence for the hypothesis that auditory temporal processing, as measured by the decrement (short-term habituation) of the major auditory evoked component, the N1m wave, is impaired in aging. The differences between these magnetoencephalographic findings and previously published behavioral data might be explained by differences in the experimental setting between the present study and previous behavioral studies, in terms of speech rate, attention, and masking noise. Significantly larger amplitudes of the P1m and N1m waves suggest that the cortical processing of individual sounds differs between younger and older individuals. This result adds to the growing evidence that brain functions, such as sensory processing, motor control and cognitive processing, can change during healthy aging, presumably due to experience-dependent neuroplastic mechanisms.

Enhanced and bilateralized visual sensory processing in the ventral stream may be a feature of normal aging

Evidence has emerged for age-related amplification of basic sensory processing indexed by early components of the visual evoked potential (VEP). However, since these age-related effects have been incidental to the main focus of these studies, it is unclear whether they are performance dependent or alternately, represent intrinsic sensory processing changes. High-density VEPs were acquired from 19 healthy elderly and 15 young control participants who viewed alphanumeric stimuli in the absence of any active task. The data show both enhanced and delayed neural responses within structures of the ventral visual stream, with reduced hemispheric asymmetry in the elderly that may be indicative of a decline in hemispheric specialization. Additionally, considerably enhanced early frontal cortical activation was observed in the elderly, suggesting frontal hyper-activation. These age-related differences in early sensory processing are discussed in terms of recent proposals that normal aging involves large-scale compensatory reorganization. Our results suggest that such compensatory mechanisms are not restricted to later higher-order cognitive processes but may also be a feature of early sensory-perceptual processes.

P50 gating deficit in Alzheimer dementia correlates to frontal neuropsychological function

BACKGROUND

Cognitive inhibition processes were found to be deficient early in the clinical course of Alzheimer's disease (AD). The inhibition of redundant information is a precondition for efficient cognitive processing and presumably modulated by prefrontal attentional networks. Deficits in the suppression of the evoked potential P50 response to paired clicks are well known in schizophrenic patients and undergo cholinergic modulation. In this study, we aimed to investigate inhibitory gating deficits of P50 in AD and their relation to neuropsychological measures.

METHOD

P50 suppression was assessed in 19 AD-patients in comparison to a young and elderly control group (n=17 each) and related to MMSE and specific neuropsychological assessments.

RESULTS

Patients showed reduced sensory gating compared to healthy elderly (p<0.021) and exhibited significantly higher N40-P50-amplitudes. There were no age or gender effects in controls. Frontal neuropsychological tests (TMT-B, verbal fluency) and working memory requiring inhibition, but not declarative memory functions, were significantly correlated with inhibitory gating and test amplitude in both, AD-patients and controls.

CONCLUSIONS

The results support an early inhibitory deficit interfering with executive functions and working memory in AD independent from physiological aging. P50 gating might be applicable as a marker for inhibition deficits and thereby be important for prognosis estimation.