The frontoparietal multiple demand network interacts with the dual pathways in auditory working memory.

The frontoparietal multiple demand (MD) network has been proposed as a control network that regulates processing demands while enabling goal-directed actions. This study tested the MD network account in auditory working memory (AWM) and identified its functional role and relationship with the dual pathways model in AWM, where segregation of function was based on the sound domain. Forty-one healthy young adults performed an n-back task consisting of an orthogonal combination of the sound domain (spatial versus nonspatial) and cognitive operation (low load versus high load). Functional connectivity and correlation analyses were performed to assess the connectivity of the MD network and the dual pathways. Our results confirmed the contribution of the MD network to AWM and identified its interactions with the dual pathways in both sound domains and during high and low load levels. At high loads, the strength of connectivity with the MD network correlated with task accuracy, indicating the key role of the MD network in supporting successful performance as cognitive load increases. This study contributed to the auditory literature by showing that both the MD network and dual pathways collaborate with each other to support AWM, and neither of them alone is adequate to explain auditory cognition.

Reactivating ordinal position information from auditory sequence memory in human brains.

Retaining a sequence of events in their order is a core ability of many cognitive functions, such as speech recognition, movement control, and episodic memory. Although content representations have been widely studied in working memory (WM), little is known about how ordinal position information of an auditory sequence is retained in the human brain as well as its coding characteristics. In fact, there is still a lack of an efficient approach to directly accessing the stored ordinal position code during WM retention. Here, 31 participants performed an auditory sequence WM task with their brain activities recorded using electroencephalography (EEG). We developed new triggering events that could successfully reactivate neural representations of ordinal position during the delay period. Importantly, the ordinal position reactivation is further related to recognition behavior, confirming its indexing of WM storage. Furthermore, the ordinal position code displays an intriguing "stable-dynamic" format, i.e. undergoing the same dynamic neutral trajectory in the multivariate neural space during both encoding and retention (whenever reactivated). Overall, our results provide an effective approach to accessing the behaviorally-relevant ordinal position information in auditory sequence WM and reveal its new temporal characteristics.

The relationship between speech in noise perception and auditory working memory capacity in monolingual and bilingual adults.

OBJECTIVE: Speech-in-noise perception is dependent on the interaction between sensory and cognitive processes. One factor that can relate to both processes is bilingualism. This study aimed to determine the correlation between auditory-working-memory and speech-in-noise in Persian monolinguals and Kurdish-Persian bilinguals. DESIGN: Speech-in-noise tests (sentences-in-noise and syllables-in-noise) and auditory-working-memory tests (forward and backward digit span, and n-back) were performed. STUDY SAMPLE: Participants were 48 Kurdish-Persian bilinguals with a mean age of 24 (±4) years and 48 Persian monolinguals with a mean age of 25 (±2) years with normal hearing. RESULTS: Both language groups scored within normal limits in all memory and speech-in-noise tests. However, bilinguals performed significantly worse than monolinguals on all auditory-working-memory tests and the sentences-in-noise test. Monolinguals outperformed bilinguals in sentences-in-noise test (∼1.5 dB difference) and all auditory-working-memory tests (∼1 digit difference). The two groups did not significantly differ in syllables-in-noise test. Both groups had a significant correlation between working memory capacity and sentences-in-noise test. However, no significant correlation was found between syllables-in-noise and working memory capacity at any SNR. CONCLUSIONS: Cognitive factors such as auditory working memory appear to correlate with speech-in-noise perception ability (at least at the sentence level) in monolingual and bilinguals young adults.

Precise Topology of Adjacent Domain-General and Sensory-Biased Regions in the Human Brain.

Recent functional MRI studies identified sensory-biased regions across much of the association cortices and cerebellum. However, their anatomical relationship to multiple-demand (MD) regions, characterized as domain-general due to their coactivation during multiple cognitive demands, remains unclear. For a better anatomical delineation, we used multimodal MRI techniques of the Human Connectome Project to scan subjects performing visual and auditory versions of a working memory (WM) task. The contrast between hard and easy WM showed strong domain generality, with essentially identical patterns of cortical, subcortical, and cerebellar MD activity for visual and auditory materials. In contrast, modality preferences were shown by contrasting easy WM with baseline; most MD regions showed visual preference while immediately adjacent to cortical MD regions, there were interleaved regions of both visual and auditory preference. The results may exemplify a general motif whereby domain-specific regions feed information into and out of an adjacent, integrative MD core.

Distributed networks for auditory memory differentially contribute to recall precision.

Re-directing attention to objects in working memory can enhance their representational fidelity. However, how this attentional enhancement of memory representations is implemented across distinct, sensory and cognitive-control brain network is unspecified. The present fMRI experiment leverages psychophysical modelling and multivariate auditory-pattern decoding as behavioral and neural proxies of mnemonic fidelity. Listeners performed an auditory syllable pitch-discrimination task and received retro-active cues to selectively attend to a to-be-probed syllable in memory. Accompanied by increased neural activation in fronto-parietal and cingulo-opercular networks, valid retro-cues yielded faster and more perceptually sensitive responses in recalling acoustic detail of memorized syllables. Information about the cued auditory object was decodable from hemodynamic response patterns in superior temporal sulcus (STS), fronto-parietal, and sensorimotor regions. However, among these regions retaining auditory memory objects, neural fidelity in the left STS and its enhancement through attention-to-memory best predicted individuals' gain in auditory memory recall precision. Our results demonstrate how functionally discrete brain regions differentially contribute to the attentional enhancement of memory representations.

The phonological loop: is speech special?

It has been proposed that the maintenance of phonological information in verbal working memory (vWM) is carried by a domain-specific short-term storage center-the phonological loop-which is composed of a phonological store and an articulatory rehearsal system. Several brain regions including the left posterior inferior frontal gyrus (pIFG) and anterior supramarginal gyri (aSMG) are thought to support these processes. However, recent behavioral evidence suggests that verbal and non-verbal auditory information may be processed as part of a unique domain general short-term storage center instead of through specialized subsystems such as the phonological loop. In the current study, we used a single-pulse transcranial magnetic stimulation (TMS)-delayed priming paradigm with speech (syllables) and acoustically complex non-speech sounds (bird songs) to examine whether the pIFG and aSMG are involved in the processing of verbal information or, alternatively, in the processing of any complex auditory information. Our results demonstrate that TMS delivered to both regions had an effect on performance for speech and non-speech stimuli, but the nature of the effect was different. That is, priming was reduced for the speech sounds because TMS facilitated the detection of different but not identical stimuli, and accuracy was decreased for non-speech sounds. Since TMS interfered with both speech and non-speech sounds, these findings support the existence of an auditory short-term storage center located within the dorsal auditory stream.

Modality effects in verbal working memory updating: Transcranial direct current stimulation over human inferior frontal gyrus and posterior parietal cortex.

Verbal working memory (VWM) involves visual and auditory verbal information. Neuroimaging studies have shown significant modality effects for VWM in the left posterior parietal cortex (PPC). The left inferior frontal gyrus (IFG) is more sensitive to auditory and phonological information. However, much less is known about the effects of transcranial direct current stimulation (tDCS) over the left PPC and IFG on different sensory modalities of VWM (auditory vs. visual). Therefore, the present study aimed to examine whether tDCS over the left PPC and IFG affects visual and auditory VWM updating performance using a single-blind design. Fifty-one healthy participants were randomly assigned to three tDCS groups (left PPC/left IFG/sham) and were asked to complete both the visual and auditory letter 3-back tasks. Results showed that stimulating the left PPC enhanced the response efficiency of visual, but not auditory, VWM compared with the sham condition. Anodal stimulation to the left IFG improved the response efficiency of both tasks. The present study revealed a modality effect of VWM in the left PPC, while the left IFG had a causal role in VWM updating of different sensory modalities.

Overlapping Anatomical Networks Convey Cross-Modal Suppression in the Sighted and Coactivation of "Visual" and Auditory Cortex in the Blind.

In the present combined DTI/fMRI study we investigated adaptive plasticity of neural networks involved in controlling spatial and nonspatial auditory working memory in the early blind (EB). In both EB and sighted controls (SC), fractional anisotropy (FA) within the right inferior longitudinal fasciculus correlated positively with accuracy in a one-back sound localization but not sound identification task. The neural tracts passing through the cluster of significant correlation connected auditory and "visual" areas in the right hemisphere. Activity in these areas during both sound localization and identification correlated with FA within the anterior corpus callosum, anterior thalamic radiation, and inferior fronto-occipital fasciculus. In EB, FA in these structures correlated positively with activity in both auditory and "visual" areas, whereas FA in SC correlated positively with activity in auditory and negatively with activity in visual areas. The results indicate that frontal white matter conveys cross-modal suppression of occipital areas in SC, while it mediates coactivation of auditory and reorganized "visual" cortex in EB.

Assessment of auditory working memory in normal hearing adults with tinnitus.

PURPOSE: Tinnitus is characterized by the perception of sound without an existing external stimulus. The presence of tinnitus might be intolerable for many and can be sufficiently troublesome in hearing, sleep, thought processing, and other functional abilities, all of which can negatively impact the quality of life. Individuals with tinnitus may have decreased cognitive efficiency because tinnitus can adversely affect the other tasks being performed. The present study was taken up to evaluate auditory working memory using digit span tasks in adults with tinnitus. METHODS: The tasks administered included forward, backward, ascending, and descending digit span. Tinnitus Handicap Inventory questionnaire was administered on all the individuals with tinnitus, and also, it was attempted to correlate the scores of auditory working memory with that of tinnitus handicap inventory. RESULTS: The results indicated poorer scores for backward, ascending and descending digit span task and no significant difference for the forward digit span task. There was no correlation between auditory working memory tasks and overall tinnitus handicap scores along with its sub-scales. CONCLUSION: It was concluded that tinnitus disrupts the functioning of auditory working memory and is governed by the annoyance caused by tinnitus.

Association of salivary alpha-amylase and salivary flow rate with working memory functioning in healthy children.

The aim of this study was to examine the association between auditory and visual working memory (WM) performance and salivary alpha-amylase (sAA) and salivary flow rate (SFR) in a sample of 63 children (38 boys). WM was assessed by means of WISC-V subtests: four auditory subtests (Digit Span and Letter-Number Sequencing) and one visual subtest (Picture Span). SAA activity, output, and SFR were measured at baseline (10 min prior to testing), one minute prior to testing, one minute after the end of the auditory WM subtests and one minute after the end of the visual WM subtest. Our statistical analyses showed an association among SAA activity, output and SFR levels and the number of recalled digits in the last attempt score in Letter-Number Sequencing subtest. Specifically, our results showed that working performance in this task was associated with a concurrent decrease in SFR (r(63) = -0.423, p < .05). This salivary measure was the best predictor of this specific index of working memory performance (ß = -0.423, p < .05). These results show that the changes in SFR, which represents changes in parasympathetic tone, could be employed in future studies as a noninvasive marker of working memory performance in child studies.

Dopaminergic modulation of hemodynamic signal variability and the functional connectome during cognitive performance.

Dopamine underlies important aspects of cognition, and has been suggested to boost cognitive performance. However, how dopamine modulates the large-scale cortical dynamics during cognitive performance has remained elusive. Using functional MRI during a working memory task in healthy young human listeners, we investigated the effect of levodopa (l-dopa) on two aspects of cortical dynamics, blood oxygen-level-dependent (BOLD) signal variability and the functional connectome of large-scale cortical networks. We here show that enhanced dopaminergic signaling modulates the two potentially interrelated aspects of large-scale cortical dynamics during cognitive performance, and the degree of these modulations is able to explain inter-individual differences in l-dopa-induced behavioral benefits. Relative to placebo, l-dopa increased BOLD signal variability in task-relevant temporal, inferior frontal, parietal and cingulate regions. On the connectome level, however, l-dopa diminished functional integration across temporal and cingulo-opercular regions. This hypo-integration was expressed as a reduction in network efficiency and modularity in more than two thirds of the participants and to different degrees. Hypo-integration co-occurred with relative hyper-connectivity in paracentral lobule and precuneus, as well as posterior putamen. Both, l-dopa-induced BOLD signal variability modulation and functional connectome modulations proved predictive of an individual's l-dopa-induced benefits in behavioral performance, namely response speed and perceptual sensitivity. Lastly, l-dopa-induced modulations of BOLD signal variability were correlated with l-dopa-induced modulation of nodal connectivity and network efficiency. Our findings underline the role of dopamine in maintaining the dynamic range of, and communication between, cortical systems, and their explanatory power for inter-individual differences in benefits from dopamine during cognitive performance.

Nonverbal auditory working memory: Can music indicate the capacity?

Different working memory (WM) mechanisms that underlie words, tones, and timbres have been proposed in previous studies. In this regard, the present study developed a WM test with nonverbal sounds and compared it to the conventional verbal WM test. A total of twenty-five, non-music major, right-handed college students were presented with four different types of sounds (words, syllables, pitches, timbres) that varied from two to eight digits in length. Both accuracy and oxygenated hemoglobin (oxyHb) were measured. The results showed significant effects of number of targets on accuracy and sound type on oxyHb. A further analysis showed prefrontal asymmetry with pitch being processed by the right hemisphere (RH) and timbre by the left hemisphere (LH). These findings suggest a potential for employing musical sounds (i.e., pitch and timbre) as a complementary stimuli for conventional nonverbal WM tests, which can additionally examine its asymmetrical roles in the prefrontal regions.

Infant auditory short-term memory for non-linguistic sounds.

This research explores auditory short-term memory (STM) capacity for non-linguistic sounds in 10-month-old infants. Infants were presented with auditory streams composed of repeating sequences of either 2 or 4 unique instruments (e.g., flute, piano, cello; 350 or 700 ms in duration) followed by a 500-ms retention interval. These instrument sequences either stayed the same for every repetition (Constant) or changed by 1 instrument per sequence (Varying). Using the head-turn preference procedure, infant listening durations were recorded for each stream type (2- or 4-instrument sequences composed of 350- or 700-ms notes). Preference for the Varying stream was taken as evidence of auditory STM because detection of the novel instrument required memory for all of the instruments in a given sequence. Results demonstrate that infants listened longer to Varying streams for 2-instrument sequences, but not 4-instrument sequences, composed of 350-ms notes (Experiment 1), although this effect did not hold when note durations were increased to 700 ms (Experiment 2). Experiment 3 replicates and extends results from Experiments 1 and 2 and provides support for a duration account of capacity limits in infant auditory STM.

Reduced white matter maturation in the central auditory system of children living with HIV.

Introduction: School-aged children experience crucial developmental changes in white matter (WM) in adolescence. The human immunodeficiency virus (HIV) affects neurodevelopment. Children living with perinatally acquired HIV (CPHIVs) demonstrate hearing and neurocognitive impairments when compared to their uninfected peers (CHUUs), but investigations into the central auditory system (CAS) WM integrity are lacking. The integration of the CAS and other brain areas is facilitated by WM fibers whose integrity may be affected in the presence of HIV, contributing to neurocognitive impairments. Methods: We used diffusion tensor imaging (DTI) tractography to map the microstructural integrity of WM between CAS regions, including the lateral lemniscus and acoustic radiation, as well as between CAS regions and non-auditory regions of 11-year-old CPHIVs. We further employed a DTI-based graph theoretical framework to investigate the nodal strength and efficiency of the CAS and other brain regions in the structural brain network of the same population. Finally, we investigated associations between WM microstructural integrity outcomes and neurocognitive outcomes related to auditory and language processing. We hypothesized that compared to the CHUU group, the CPHIV group would have lower microstructural in the CAS and related regions. Results: Our analyses showed higher mean diffusivity (MD), a marker of axonal maturation, in the lateral lemniscus and acoustic radiations, as well as WM between the CAS and non-auditory regions predominantly in frontotemporal areas. Most affected WM connections also showed higher axial and radial diffusivity (AD and RD, respectively). There were no differences in the nodal properties of the CAS regions between groups. The MD of frontotemporal and subcortical WM-connected CAS regions, including the inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, and internal capsule showed negative associations with sequential processing in the CPHIV group but not in the CHUU group. Discussion: The current results point to reduced axonal maturation in WM, marked by higher MD, AD, and RD, within and from the CAS. Furthermore, alterations in WM integrity were associated with sequential processing, a neurocognitive marker of auditory working memory. Our results provide insights into the microstructural integrity of the CAS and related WM in the presence of HIV and link these alterations to auditory working memory.

Relationship Between Central Auditory Processing Abilities and Working Memory During Adolescence.

Purpose: Adolescence is a period of transformation in humans with changes in the neural physiology at subcortical and cortical levels. However, its significance on auditory processing skills and working memory skills and their association is yet to be well understood. Hence, the current study was designed to evaluate and establish the association between auditory processing skills and working memory abilities in adolescents. Method: A total of 125 adolescents within the age range of 10 to 15 years participated in the current study. All of them had normal hearing sensitivity and no associated obvious peripheral or central deficits. All the participants underwent auditory closure ability assessment using quick speech perception in noise test in Kannada, binaural integration ability assessment using dichotic CV test, and temporal processing assessment using gap detection test. Auditory working memory abilities were assessed using auditory digit span and digit sequencing. Results: Spearman correlation was done to assess the correlation between auditory processing skills and working memory abilities. Results revealed a significant negative correlation between most of the central auditory processing abilities and all the working memory spans. Conclusions: Findings of the current study indicate that individuals with poor working memory abilities have difficulty in auditory processing abilities.

Functional near-infrared spectroscopy measures of neural activity in children with and without developmental language disorder during a working memory task.

INTRODUCTION: Children with developmental language disorder (DLD) exhibit cognitive deficits that interfere with their ability to learn language. Little is known about the functional neuroanatomical differences between children developing typically (TD) and children with DLD. METHODS: Using functional near-infrared spectroscopy, we recorded oxygenated hemoglobin (O2 hb) concentration values associated with neural activity in children with and without DLD during an auditory N-back task that included 0-back, 1-back, and 2-back conditions. Analyses focused on the left dorsolateral prefrontal cortex (DLPFC) and left inferior parietal lobule (IPL). Multilevel models were constructed with accuracy, response time, and O2 hb as outcome measures, with 0-back outcomes as fixed effects to control for sustained attention. RESULTS: Children with DLD were significantly less accurate than their TD peers at both the 1-back and 2-back tasks, and they demonstrated slower response times during 2-back. In addition, children in the TD group demonstrated significantly greater sensitivity to increased task difficulty, showing increased O2 hb to the IPL during 1-back and to the DLPFC during the 2-back, whereas the DLD group did not. A secondary analysis revealed that higher O2 hb in the DLPFC predicted better task accuracy across groups. CONCLUSION: When task difficulty increased, children with DLD failed to recruit the DLPFC for monitoring information and the IPL for processing information. Reduced memory capacity and reduced engagement likely contribute to the language learning difficulties of children with DLD.

Age differences in binaural and working memory abilities in school-going children.

OBJECTIVES: Binaural hearing is the interplay of acoustic cues (interaural time differences: ITD, interaural level differences: ILD, and spectral cues) and cognitive abilities (e.g., working memory, attention). The current study investigated the effect of developmental age on auditory binaural resolution and working memory and the association between them (if any) in school-going children. METHODS: Fifty-seven normal-hearing school-going children aged 6-15 y were recruited for the study. The participants were divided into three groups: Group 1 (n=17, Mage = 7.1y ± 0.72 y), Group 2 (n = 23; Mage = 10.2y ± 0.8 y), Group 3 (n = 17; Mage: 14.1 y ±1.3 y). Group 4, with normal hearing young adults (n = 20; Mage = 21.1 y± 3.2 y), was included for comparing the maturational changes in former groups with adult values. Tests of binaural resolution (ITD and ILD thresholds) and auditory working memory (forward and backward digit span and 2n-back digit) were administered to all the participants. RESULTS: Results indicated a main effect of age on spatial resolution and working memory, with the median of lower age groups (Group 1 & Group 2) being significantly poorer (p < 0.01) than the higher age groups (Group 3 & Group 4). Groups 2, 3, and 4 performed significantly better than Group 1 (p < 0.001) on the forward span and ILD task. Groups 3 and 4 had significantly better ITD (p = 0.04), backward span (p = 0.02), and 2n-back scores than Group 2. A significant correlation between scores on working memory tasks and spatial resolution thresholds was also found. On discriminant function analysis, backward span and ITD emerged as sensitive measures for segregating older groups (Group 3 & Group 4) from younger groups (Group 1 & Group 2). CONCLUSIONS: The present study showed that the ILD thresholds and forward digit span mature by nine years. However, the backward digit span score continued to mature beyond 15 y. This finding can be attributed to the influence of auditory attention (a working memory process) on the binaural resolution, which is reported to mature till late adolescence.

Comparing auditory and visual aspects of multisensory working memory using bimodally matched feature patterns.

Working memory (WM) reflects the transient maintenance of information in the absence of external input, which can be attained via multiple senses separately or simultaneously. Pertaining to WM, the prevailing literature suggests the dominance of vision over other sensory systems. However, this imbalance may be stemming from challenges in finding comparable stimuli across modalities. Here, we addressed this problem by using a balanced multisensory retro-cue WM design, which employed combinations of auditory (ripple sounds) and visuospatial (Gabor patches) patterns, adjusted relative to each participant's discrimination ability. In three separate experiments, the participant was asked to determine whether the (retro-cued) auditory and/or visual items maintained in WM matched or mismatched the subsequent probe stimulus. In Experiment 1, all stimuli were audiovisual, and the probes were either fully mismatching, only partially mismatching, or fully matching the memorized item. Experiment 2 was otherwise same as Experiment 1, but the probes were unimodal. In Experiment 3, the participant was cued to maintain only the auditory or visual aspect of an audiovisual item pair. In two of the three experiments, the participant matching performance was significantly more accurate for the auditory than visual attributes of probes. When the perceptual and task demands are bimodally equated, auditory attributes can be matched to multisensory items in WM at least as accurately as, if not more precisely than, their visual counterparts.

Effect of Carnatic Music Listening Training on Speech in Noise Performance in Adults.

BACKGROUND AND OBJECTIVES: Music listening has a concomitant effect on structural and functional organization of the brain. It helps in relaxation, mind training and neural strengthening. In relation to it, the present study was aimed to find the effect of Carnatic music listening training (MLT) on speech in noise performance in adults. SUBJECTS AND METHODS: A total of 28 participants (40-70 years) were recruited in the study. Based on randomized control trial, they were divided into intervention and control group. Intervention group underwent a short-term MLT. Quick Speech-in-Noise in Kannada was used as an outcome measure. RESULTS: Results were analysed using mixed method analysis of variance (ANOVA) and repeated measures ANOVA. There was a significant difference between intervention and control group post MLT. The results of the second continuum revealed no statistically significant difference between post training and follow-up scores in both the groups. CONCLUSIONS: In conclusion short-term MLT resulted in betterment of speech in noise performance. MLT can be hence used as a viable tool in formal auditory training for better prognosis.

Oscillatory correlates of auditory working memory examined with human electrocorticography.

This work examines how sounds are held in auditory working memory (AWM) in humans by examining oscillatory local field potentials (LFPs) in candidate brain regions. Previous fMRI studies by our group demonstrated blood oxygenation level-dependent (BOLD) response increases during maintenance in auditory cortex, inferior frontal cortex and the hippocampus using a paradigm with a delay period greater than 10s. The relationship between such BOLD changes and ensemble activity in different frequency bands is complex, and the long delay period raised the possibility that long-term memory mechanisms were engaged. Here we assessed LFPs in different frequency bands in six subjects with recordings from all candidate brain regions using a paradigm with a short delay period of 3 s. Sustained delay activity was demonstrated in all areas, with different patterns in the different areas. Enhancement in low frequency (delta) power and suppression across higher frequencies (beta/gamma) were demonstrated in primary auditory cortex in medial Heschl's gyrus (HG) whilst non-primary cortex showed patterns of enhancement and suppression that altered at different levels of the auditory hierarchy from lateral HG to superior- and middle-temporal gyrus. Inferior frontal cortex showed increasing suppression with increasing frequency. The hippocampus and parahippocampal gyrus showed low frequency increases and high frequency decreases in oscillatory activity. This work demonstrates sustained activity patterns during AWM maintenance, with prominent low-frequency increases in medial temporal lobe regions.