Neural circuits in auditory and audiovisual memory

Semantically congruent bimodal presentation modulates cognitive control over attentional guidance by working memory

Although previous studies have well established that audiovisual enhancement has a promoting effect on working memory and selective attention, there remains an open question about the influence of audiovisual enhancement on attentional guidance by working memory. To address this issue, the present study adopted a dual-task paradigm that combines a working memory task and a visual search task, in which the content of working memory was presented in audiovisual or visual modalities. Given the importance of search speed in memory-driven attentional suppression, we divided participants into two groups based on their reaction time (RT) in neutral trials and examined whether audiovisual enhancement in attentional suppression was modulated by search speed. The results showed that the slow search group exhibited a robust memory-driven attentional suppression effect, and the suppression effect started earlier and its magnitude was greater in the audiovisual condition than in the visual-only condition. However, among the faster search group, the suppression effect only occurred in the trials with longer RTs in the visual-only condition, and its temporal dynamics were selectively improved in the audiovisual condition. Furthermore, audiovisual enhancement of memory-driven attention evolved over time. These findings suggest that semantically congruent bimodal presentation can progressively facilitate the strength and temporal dynamics of memory-driven attentional suppression, and that search speed plays an important role in this process. This may be due to a synergistic effect between multisensory working memory representation and top-down suppression mechanism. The present study demonstrates the flexible role of audiovisual enhancement on cognitive control over memory-driven attention.

Differences in brain functional networks for audiovisual integration during reading between children and adults

Building robust letter-to-sound correspondences is a prerequisite for developing reading capacity. However, the neural mechanisms underlying the development of audiovisual integration for reading are largely unknown. This study used functional magnetic resonance imaging in a lexical decision task to investigate functional brain networks that support audiovisual integration during reading in developing child readers (10-12 years old) and skilled adult readers (20-28 years old). The results revealed enhanced connectivity in a prefrontal-superior temporal network (including the right medial frontal gyrus, right superior frontal gyrus, and left superior temporal gyrus) in adults relative to children, reflecting the development of attentional modulation of audiovisual integration involved in reading processing. Furthermore, the connectivity strength of this brain network was correlated with reading accuracy. Collectively, this study, for the first time, elucidates the differences in brain networks of audiovisual integration for reading between children and adults, promoting the understanding of the neurodevelopment of multisensory integration in high-level human cognition.

The electrophysiological masking level difference: effects of age and mediation of hearing and cognition

OBJECTIVE

Evaluate the conceptual framework that age effects on the electrophysiological binaural masking level difference (MLD) are partially mediated by age-related hearing loss and/or global cognitive function via mediation analysis.

DESIGN

Participants underwent a series of audiometric tests. The MLD was measured via cortical auditory evoked potentials using a speech stimulus (/ɑ/) in speech-weighted background noise. We used mediation analyses to determine the total effect, natural direct effects, and natural indirect effects, which are displayed as regression coefficients ([95% CI]; p value).

STUDY SAMPLE

Twenty-eight individuals aged 19-87 years (mean [SD]: 53.3 [25.2]), recruited from the community.

RESULTS

Older age had a significant total effect on the MLD (-0.69 [95% CI: -0.96, -0.45]; p < 0.01). Neither pure tone average (-0.11 [95% CI: -0.43, 0.24; p = 0.54] nor global cognitive function (-0.02 [95% CI: -0.13, 0.02]; p = 0.55) mediated the relationship of age and the MLD and effect sizes were small. Results were insensitive to use of alternative hearing measures or inclusion of interaction terms.

CONCLUSIONS

The electrophysiological MLD may be an age-sensitive measure of binaural temporal processing that is minimally affected by age-related hearing loss and global cognitive function.

Representation of expression and identity by ventral prefrontal neurons

Evidence has suggested that the ventrolateral prefrontal cortex (VLPFC) processes social stimuli, including faces and vocalizations, which are essential for communication. Features embedded within audiovisual stimuli, including emotional expression and caller identity, provide abundant information about an individual's intention, emotional state, motivation, and social status, which are important to encode in a social exchange. However, it is unknown to what extent the VLPFC encodes such features. To investigate the role of VLPFC during social communication, we recorded single-unit activity while rhesus macaques (Macaca mulatta) performed a nonmatch-to-sample task using species-specific face-vocalization stimuli that differed in emotional expression or caller identity. 75% of recorded cells were task-related and of these >70% were responsive during the nonmatch period. A larger proportion of nonmatch cells encoded the stimulus rather than the context of the trial type. A subset of responsive neurons were most commonly modulated by the identity of the nonmatch stimulus and less by the emotional expression, or both features within the face-vocalization stimuli presented during the nonmatch period. Neurons encoding identity were found in VLPFC across a broader region than expression related cells which were confined to only the anterolateral portion of the recording chamber in VLPFC. These findings suggest that, within a working memory paradigm, VLPFC processes features of face and vocal stimuli, such as emotional expression and identity, in addition to task and contextual information. Thus, stimulus and contextual information may be integrated by VLPFC during social communication.

Short-Term Audiovisual Spatial Training Enhances Electrophysiological Correlates of Auditory Selective Spatial Attention

Audiovisual cross-modal training has been proposed as a tool to improve human spatial hearing. Here, we investigated training-induced modulations of event-related potential (ERP) components that have been associated with processes of auditory selective spatial attention when a speaker of interest has to be localized in a multiple speaker ("cocktail-party") scenario. Forty-five healthy participants were tested, including younger (19-29 years; n = 21) and older (66-76 years; n = 24) age groups. Three conditions of short-term training (duration 15 min) were compared, requiring localization of non-speech targets under "cocktail-party" conditions with either (1) synchronous presentation of co-localized auditory-target and visual stimuli (audiovisual-congruency training) or (2) immediate visual feedback on correct or incorrect localization responses (visual-feedback training), or (3) presentation of spatially incongruent auditory-target and visual stimuli presented at random positions with synchronous onset (control condition). Prior to and after training, participants were tested in an auditory spatial attention task (15 min), requiring localization of a predefined spoken word out of three distractor words, which were presented with synchronous stimulus onset from different positions. Peaks of ERP components were analyzed with a specific focus on the N2, which is known to be a correlate of auditory selective spatial attention. N2 amplitudes were significantly larger after audiovisual-congruency training compared with the remaining training conditions for younger, but not older, participants. Also, at the time of the N2, distributed source analysis revealed an enhancement of neural activity induced by audiovisual-congruency training in dorsolateral prefrontal cortex (Brodmann area 9) for the younger group. These findings suggest that cross-modal processes induced by audiovisual-congruency training under "cocktail-party" conditions at a short time scale resulted in an enhancement of correlates of auditory selective spatial attention.

Categorical Auditory Working Memory in Crows

The ability to group sensory data into behaviorally meaningful classes and to maintain these perceptual categories active in working memory is key to intelligent behavior. Here, we show that carrion crows, highly vocal and cognitively advanced corvid songbirds, possess categorical auditory working memory. The crows were trained in a delayed match-to-category task that required them to flexibly match remembered sounds based on the upward or downward shift of the sounds' frequency modulation. After training, the crows instantaneously classified novel sounds into the correct auditory categories. The crows showed sharp category boundaries as a function of the relative frequency interval of the modulation. In addition, the crows generalized frequency-modulated sounds within a category and correctly classified novel sounds kept in working memory irrespective of other acoustic features of the sound. This suggests that crows can form and actively memorize auditory perceptual categories in the service of cognitive control of their goal-directed behaviors.

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Crows performed a delayed match-to-category task with frequency modulated sounds

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Crows classified novel sounds into upward or downward modulated sound categories

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Crows showed sharp category boundaries and within-category generalization

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Crows can actively memorize auditory perceptual categories for cognitive control

Acoustic closed-loop stimulation during sleep improves consolidation of reward-related memory information in healthy children but not in children with attention-deficit hyperactivity disorder

Study Objectives

Slow oscillations (SO) during slow-wave sleep foster the consolidation of declarative memory. Children with attention-deficit hyperactivity disorder (ADHD) display deficits in the sleep-associated consolidation of declarative memory, possibly due to an altered function of SO. The present study aimed at enhancing SO activity using closed-looped acoustic stimulation during slow-wave sleep in children with ADHD.

Methods

A total of 29 male children (14 with ADHD; aged 8–12 years) participated in a double-blind, placebo-controlled study trial. Children spent two experimental nights in a sleep lab, one stimulation night and one sham night. A declarative learning task (word-pair learning) with a reward condition was used as a primary outcome. Secondary outcome variables were a procedural memory (serial reaction time) and working memory (WM; n-back) task. Encoding of declarative and procedural memory took place in the evening before sleep. After sleep, the retrieval took place followed by the n-back task.

Results

The stimulation successfully induced SO activity during sleep in children with and without ADHD. After stimulation, only healthy children performed better on high-rewarded memory items (primary outcome). In contrast, there were indications that only children with ADHD benefitted from the stimulation with respect to procedural as well as WM performance (secondary outcome).

Conclusions

We were able to show that the acoustic closed-loop stimulation can be applied to enhance SO activity in children with and without ADHD. Our data indicate that SO activity during sleep interacts with subsequent memory performance (primary outcome: rewarded declarative memory; secondary outcome: procedural and WM) in children with and without ADHD.

Fronto-parietal and temporal brain dysfunction in depression: A fMRI investigation of auditory mismatch processing

Mismatch responses reflect neural mechanisms of early cognitive processing in the auditory domain. Disturbances of these mechanisms on multiple levels of neural processing may contribute to clinical symptoms in major depression (MD). A functional magnetic resonance imaging (fMRI) study was conducted to identify neurobiological foundations of altered mismatch processing in MD. Twenty-five patients with major depression and 25 matched healthy individuals completed an auditory mismatch paradigm optimized for fMRI. Brain activity during mismatch processing was compared between groups. Moreover, seed-based connectivity analyses investigated depression-specific brain networks. In patients, mismatch processing was associated with reduced activation in the right auditory cortex as well as in a fronto-parietal attention network. Moreover, functional coupling between the right auditory cortex and frontal areas was reduced in patients. Seed-to voxel analysis on the whole-brain level revealed reduced connectivity between the auditory cortex and the thalamus as well as posterior cingulate. The present study indicates deficits in sensory processing on the level of the auditory cortex in depression. Hyposensitivity in a fronto-parietal network presumably reflects altered attention mechanisms in depression. The observed impairments may contribute to psychopathology by reducing the ability of the affected individuals to orient attention toward important environmental cues.

Not single brain areas but a network is involved in language: Applications in presurgical planning

OBJECTIVES

Language is an important human function, and is a determinant of the quality of life. In conditions such as brain lesions, disruption of the language function may occur, and lesion resection is a solution for that. Presurgical planning to determine the language-related brain areas would enhance the chances of language preservation after the operation; however, availability of a normative language template is essential.

PATIENTS AND METHODS

In this study, using data from 60 young individuals who were meticulously checked for mental and physical health, and using fMRI and robust imaging and data analysis methods, functional brain maps for the language production, perception and semantic were produced.

RESULTS

The obtained templates showed that the language function should be considered as the product of the collaboration of a network of brain regions, instead of considering only few brain areas to be involved in that.

CONCLUSION

This study has important clinical applications, and extends our knowledge on the neuroanatomy of the language function.

Attenuation of dopamine-modulated prefrontal value signals underlies probabilistic reward learning deficits in old age

Probabilistic reward learning is characterised by individual differences that become acute in aging. This may be due to age-related dopamine (DA) decline affecting neural processing in striatum, prefrontal cortex, or both. We examined this by administering a probabilistic reward learning task to younger and older adults, and combining computational modelling of behaviour, fMRI and PET measurements of DA D1 availability. We found that anticipatory value signals in ventromedial prefrontal cortex (vmPFC) were attenuated in older adults. The strength of this signal predicted performance beyond age and was modulated by D1 availability in nucleus accumbens. These results uncover that a value-anticipation mechanism in vmPFC declines in aging, and that this mechanism is associated with DA D1 receptor availability.

Dammarane Sapogenins Ameliorates Neurocognitive Functional Impairment Induced by Simulated Long-Duration Spaceflight

Increasing evidence indicates the occurrence of cognitive impairment in astronauts under spaceflight compound conditions, but the underlying mechanisms and countermeasures need to be explored. In this study, we found that learning and memory abilities were significantly reduced in rats under a simulated long-duration spaceflight environment (SLSE), which includes microgravity, isolation confinement, noises, and altered circadian rhythms. Dammarane sapogenins (DS), alkaline hydrolyzed products of ginsenosides, can enhance cognition function by regulating brain neurotransmitter levels and inhibiting SLSE-induced neuronal injury. Bioinformatics combined with experimental verification identified that the PI3K-Akt-mTOR pathway was inhibited and the MAPK pathway was activated during SLSE-induced cognition dysfunction, whereas DS substantially ameliorated the changes in brain. These findings defined the characteristics of SLSE-induced cognitive decline and the mechanisms by which DS improves it. The results provide an effective candidate for improving cognitive function in spaceflight missions.

Tactile Stimulation of the Face and the Production of Facial Expressions Activate Neurons in the Primate Amygdala

The majority of neurophysiological studies that have explored the role of the primate amygdala in the evaluation of social signals have relied on visual stimuli such as images of facial expressions. Vision, however, is not the only sensory modality that carries social signals. Both humans and nonhuman primates exchange emotionally meaningful social signals through touch. Indeed, social grooming in nonhuman primates and caressing touch in humans is critical for building lasting and reassuring social bonds. To determine the role of the amygdala in processing touch, we recorded the responses of single neurons in the macaque amygdala while we applied tactile stimuli to the face. We found that one-third of the recorded neurons responded to tactile stimulation. Although we recorded exclusively from the right amygdala, the receptive fields of 98% of the neurons were bilateral. A fraction of these tactile neurons were monitored during the production of facial expressions and during facial movements elicited occasionally by touch stimuli. Firing rates arising during the production of facial expressions were similar to those elicited by tactile stimulation. In a subset of cells, combining tactile stimulation with facial movement further augmented the firing rates. This suggests that tactile neurons in the amygdala receive input from skin mechanoceptors that are activated by touch and by compressions and stretches of the facial skin during the contraction of the underlying muscles. Tactile neurons in the amygdala may play a role in extracting the valence of touch stimuli and/or monitoring the facial expressions of self during social interactions.