Functional Differences in the Neural Substrates of Auditory Cognition as a Consequence of Music Training

Previous studies have demonstrated that musical deviants (syntactically irregular chords) elicit event related potentials/fields with negative polarity; specifically, the early right anterior negativity and the right anterior temporal negativity responses with peak latencies at ~200 ms and ~350 ms, respectively, post stimulus onset. Here, we investigated differences in the neural dynamics of the auditory perceptual system of individuals with music training compared to those with no music training. Magnetoencephalography was used to examine the neural response to a deviant sound when the auditory system was primed using stimulus entrainment to evoke an auditory gamma-band response between 31 Hz and 39 Hz, in 2 Hz steps. Participants responded to the harmonic relationship between the entrainment stimulus and the subsequent target stimulus. Gamma frequencies carry stimulus information; thus, the paradigm primed the auditory system with a known gamma frequency and evaluated any improvement in the brains response to a deviant stimulus. The entrainment stimuli did not elicit an early right anterior negativity response. Furthermore, the source location of the event-related field difference during the later right anterior temporal negativity response time-window varied depending on group and entrainment condition. In support of previous findings from research using this, and a functionally similar visual-priming paradigm, a 7 Hz phase modulation of gamma amplitude was found for non-musicians following 33 Hz stimulus entrainment. Overall, significant effects of gamma entrainment were found more frequently in the non-music brain. By contrast, musicians demonstrated a greater range of interactions with slower brain rhythms, indicative of increased top-down control.

Silence, Solitude, and Serotonin: Neural Mechanisms Linking Hearing Loss and Social Isolation

For social animals that communicate acoustically, hearing loss and social isolation are factors that independently influence social behavior. In human subjects, hearing loss may also contribute to objective and subjective measures of social isolation. Although the behavioral relationship between hearing loss and social isolation is evident, there is little understanding of their interdependence at the level of neural systems. Separate lines of research have shown that social isolation and hearing loss independently target the serotonergic system in the rodent brain. These two factors affect both presynaptic and postsynaptic measures of serotonergic anatomy and function, highlighting the sensitivity of serotonergic pathways to both types of insult. The effects of deficits in both acoustic and social inputs are seen not only within the auditory system, but also in other brain regions, suggesting relatively extensive effects of these deficits on serotonergic regulatory systems. Serotonin plays a much-studied role in depression and anxiety, and may also influence several aspects of auditory cognition, including auditory attention and understanding speech in challenging listening conditions. These commonalities suggest that serotonergic pathways are worthy of further exploration as potential intervening mechanisms between the related conditions of hearing loss and social isolation, and the affective and cognitive dysfunctions that follow.

Does hearing loss lead to dementia? A review of the literature

Recent studies have revealed a correlation between aging-related hearing loss and the likelihood of developing Alzheimer Disease. However, it is not yet known if the correlation simply reflects the fact that these two disorders share common risk factors or whether there is a causal link between them. The answer to this question carries therapeutic implications. Unfortunately, it is not possible to study the question of causality between aging-related hearing loss and dementia in human subjects. Here, we evaluate the research surrounding induced-hearing loss in animal models on non-auditory cognition to help infer if there is any causal evidence linking hearing loss and a more general dementia. We find ample evidence that induction of hearing loss in animals produces cognitive decline, particularly hippocampal dysfunction. The data suggest that noise-exposure produces a toxic milieu in the hippocampus consisting of a spike in glucocorticoid levels, elevations of mediators of oxidative stress and excitotoxicity, which as a consequence induce cessation of neurogenesis, synaptic loss and tau hyperphosphorylation. These data suggest that hearing loss can lead to pathological hallmarks similar to those seen in Alzheimer’s Disease and other dementias. However, the rodent data do not establish that hearing loss on its own can induce a progressive degenerative dementing illness. Therefore, we conclude that an additional “hit”, such as aging, APOE genotype, microvascular disease or others, may be necessary to trigger an ongoing degenerative process such as Alzheimer Disease.

Auditory cognition and perception of action video game players

A training method to improve speech hearing in noise has proven elusive, with most methods failing to transfer to untrained tasks. In contrast, transfer of visual learning to untrained tasks has been found in action video game players (AVGPs). It has been proposed that AVGP training improves underlying probabilistic thinking. However, most evidence is based on untrained visual tasks. This study aimed to expand the investigation to untrained auditory tasks to test cross-modal generalization, a tenet of learned probabilistic thinking. Eighty participants with mixed AVGP experience were tested on a visual reaction time task that has reliably shown superior performance in AVGPs compared to non-players and multi-genre video game players. Auditory cognition and perception were tested using auditory reaction time and two speech-in-noise tasks. Performance of AVGPs on the visual task replicated previous positive findings. However, no significant benefit of training was found on the auditory tasks. We suggest that, while AVGPs interact meaningfully with a rich visual environment during play, they may not interact with the games’ auditory environment. These results suggest that far transfer learning during action video game play is modality-specific and that an acoustically relevant auditory environment may be needed to improve auditory probabilistic thinking.

Aging and Central Auditory Disinhibition: Is It a Reflection of Homeostatic Downregulation or Metabolic Vulnerability?

Aging-related changes have been identified at virtually every level of the central auditory system. One of the most common findings across these nuclei is a loss of synaptic inhibition with aging, which has been proposed to be at the heart of several aging-related changes in auditory cognition, including diminished speech perception in complex environments and the presence of tinnitus. Some authors have speculated that downregulation of synaptic inhibition is a consequence of peripheral deafferentation and therefore is a homeostatic mechanism to restore excitatory/inhibitory balance. As such, disinhibition would represent a form of maladaptive plasticity. However, clinical data suggest that deafferentation-related disinhibition tends to occur primarily in the aged brain. Therefore, aging-related disinhibition may, in part, be related to the high metabolic demands of inhibitory neurons relative to their excitatory counterparts. These findings suggest that both deafferentation-related maladaptive plastic changes and aging-related metabolic factors combine to produce changes in central auditory function. Here, we explore the arguments that downregulation of inhibition may be due to homeostatic responses to diminished afferent input vs. metabolic vulnerability of inhibitory neurons in the aged brain. Understanding the relative importance of these mechanisms will be critical for the development of treatments for the underlying causes of aging-related central disinhibition.

PITCH MEMORY AND EXPOSURE EFFECTS: Statistical learning and the effects of implicit "absolute pitch" on the perception and evaluation of music

Recent studies indicate that the ability to represent absolute pitch values in long-term memory (LTM), long believed to be the possession of a small minority of trained musicians endowed with "absolute pitch" (AP), is in fact shared to some extent by a considerable proportion of the population. The current study examined whether this newly discovered ability affects aspects of music and auditory cognition, particularly pitch learning and evaluation. Our starting points are two well established premises: (1) frequency of occurrence has an influence on the way we process stimuli; (2) in Western music, some pitches and musical keys are much more frequent than others. Based on these premises, we hypothesize that if absolute pitch values are indeed represented in LTM, pitch frequency of occurrence in music would significantly affect cognitive processes, in particular pitch learning and evaluation. Two experiments were designed to test this hypothesis in participants with no AP, most with little or no musical training. Experiment 1 demonstrated a faster response and a learning advantage for frequent pitches over infrequent pitches in an identification task. In Experiment 2 participants evaluated infrequent pitches as more pleasing than frequent pitches when presented in isolation. These results suggest that absolute pitch representation in memory may play a substantial, hitherto unacknowledged role in auditory (and specifically musical) cognition.