Motor imagery of speech:the involvement of primary motor cortex in manual and articulatory motor imagery

Motor imagery refers to the phenomenon of imagining performing an action without action execution. Motor imagery and motor execution are assumed to share a similar underlying neural system that involves primary motor cortex (M1). Previous studies have focused on motor imagery of manual actions, but articulatory motor imagery has not been investigated. In this study, transcranial magnetic stimulation (TMS) was used to elicit motor-evoked potentials (MEPs) from the articulatory muscles [orbicularis oris (OO)] as well as from hand muscles [first dorsal interosseous (FDI)]. Twenty participants were asked to execute or imagine performing a simple squeezing task involving a pair of tweezers, which was comparable across both effectors. MEPs were elicited at six time points (50, 150, 250, 350, 450, 550 ms post-stimulus) to track the time course of M1 involvement in both lip and hand tasks. The results showed increased MEP amplitudes for action execution compared to rest for both effectors at time points 350, 450 and 550 ms, but we found no evidence of increased cortical activation for motor imagery. The results indicate that motor imagery does not involve M1 for simple tasks for manual or articulatory muscles. The results have implications for models of mental imagery of simple articulatory gestures, in that no evidence is found for somatotopic activation of lip muscles in sub-phonemic contexts during motor imagery of such tasks, suggesting that motor simulation of relatively simple actions does not involve M1

The causal role of left and right superior temporal gyri in speech perception in noise:A Transcranial Magnetic Stimulation Study

Successful perception of speech in everyday listening conditions requires effective listening strategies to overcome common acoustic distortions, such as background noise. Convergent evidence from neuroimaging and clinical studies identify activation within the temporal lobes as key to successful speech perception. However, current neurobiological models disagree on whether the left temporal lobe is sufficient for successful speech perception or whether bilateral processing is required. We addressed this issue using TMS to selectively disrupt processing in either the left or right superior temporal gyrus (STG) of healthy participants to test whether the left temporal lobe is sufficient or whether both left and right STG are essential. Participants repeated keywords from sentences presented in background noise in a speech reception threshold task while receiving online repetitive TMS separately to the left STG, right STG, or vertex or while receiving no TMS. Results show an equal drop in performance following application of TMS to either left or right STG during the task. A separate group of participants performed a visual discrimination threshold task to control for the confounding side effects of TMS. Results show no effect of TMS on the control task, supporting the notion that the results of Experiment 1 can be attributed to modulation of cortical functioning in STG rather than to side effects associated with online TMS. These results indicate that successful speech perception in everyday listening conditions requires both left and right STG and thus have ramifications for our understanding of the neural organization of spoken language processing

The Effects of Age-Related Hearing Loss on the Brain and Cognitive Function

Age-related hearing loss is a common problem for older adults, leading to communication difficulties, isolation, and cognitive decline. Recently, hearing loss has been identified as potentially the most modifiable risk factor for dementia. Listening in challenging situations, or when the auditory system is damaged, strains cortical resources, which may change how the brain responds to cognitively demanding situations more generally. Here, we review the effects of age-related hearing loss on brain areas involved in speech perception, from the auditory cortex, through attentional networks, to the motor system. We explore current perspectives on the possible causal relation between hearing loss, neural reorganisation, and cognitive impairment. Through this synthesis we aim to inspire innovative research and novel interventions for ameliorating hearing loss and cognitive decline

Motor imagery alone drives corticospinal excitability during concurrent action observation and motor imagery

We studied the motor simulation processes involved in concurrent action observation and motor imagery (AO+MI) using motor evoked potentials induced by transcranial magnetic stimulation. During congruent AO+MI, participants were shown videos of a model’s hand performing rhythmical finger movements, and they imagined moving the same finger of their own hand in synchrony with the observed finger. During incongruent AO+MI, the imagery task involved a different finger from the observed one. As expected, congruent AO+MI yielded robust facilitatory effects, relative to baseline, only in the effector involved in the task. Incongruent AO+MI produced equally pronounced effects in the effector that was engaged in MI, whilst no corticospinal facilitation was found for the effector corresponding to the observed action. We further replicated that engaging in pure AO without MI does not produce reliable effects. These results do not support the proposal that observed and imagined action are both simulated at the level of the primary motor cortex. Rather, motor imagery alone can sufficiently explain the observed effects in both AO+MI conditions. This bears clear implications for the application of AO+MI procedures in sport and neurorehabilitation

Getting the Brain into Gear – An Online Study

Healthy ageing is related to word-finding difficulties. Cognitive reserve (CR) is defined as the ability to use cognitive processes efficiently and flexibly, to compensate for age-related cognitive decline. CR is measured through lifetime experiences (e.g education) and social and intellectually stimulating activities. We aimed to investigate the relationship between age-related word-finding difficulties and CR in 90 healthy adults aged between 18-30, 40-55, and 65-80 years (30 participants per group). The participants were right-handed, monolingual speakers of British English. We quantified CR through questionnaires on lifetime experiences. With use of the audio-recording function in Gorilla, we investigated word-finding abilities through picture-naming and verbal fluency tasks, controlling for the effects of processing speed, working memory, and executive functioning. We expect that adults aged 65-80 will have difficulties with word-finding due to age-related cognitive decline, resulting in slower reaction times in the picture-naming tasks. Since frequently used words are more easily accessed from memory, we expect older participants (aged 65-80) to use a higher proportion of high-frequent words in the verbal fluency task than younger adults. Finally, we expect that high levels of CR in the older adults will result in better performance on the language tasks, resembling that of the younger adults

Effects of stimulus response compatibility on covert imitation of vowels

When we observe someone else speaking, we tend to automatically activate the corresponding speech motor patterns. When listening, we therefore covertly imitate the observed speech. Simulation theories of speech perception propose that covert imitation of speech motor patterns supports speech perception. Covert imitation of speech has been studied with interference paradigms, including the stimulus–response compatibility paradigm (SRC). The SRC paradigm measures covert imitation by comparing articulation of a prompt following exposure to a distracter. Responses tend to be faster for congruent than for incongruent distracters; thus, showing evidence of covert imitation. Simulation accounts propose a key role for covert imitation in speech perception. However, covert imitation has thus far only been demonstrated for a select class of speech sounds, namely consonants, and it is unclear whether covert imitation extends to vowels. We aimed to demonstrate that covert imitation effects as measured with the SRC paradigm extend to vowels, in two experiments. We examined whether covert imitation occurs for vowels in a consonant–vowel–consonant context in visual, audio, and audiovisual modalities. We presented the prompt at four time points to examine how covert imitation varied over the distracter’s duration. The results of both experiments clearly demonstrated covert imitation effects for vowels, thus supporting simulation theories of speech perception. Covert imitation was not affected by stimulus modality and was maximal for later time points

Modulation of intra- and inter-hemispheric connectivity between primary and premotor cortex during speech perception

Primary motor (M1) areas for speech production activate during speech perception. It has been suggested that such activation may be dependent upon modulatory inputs from premotor cortex (PMv). If and how PMv differentially modulates M1 activity during perception of speech that is easy or challenging to understand, however, is unclear. This study aimed to test the link between PMv and M1 during challenging speech perception in two experiments. The first experiment investigated intra-hemispheric connectivity between left hemisphere PMv and left M1 lip area during comprehension of speech under clear and distorted listening conditions. Continuous theta burst stimulation (cTBS) was applied to left PMv in eighteen participants (aged 18–35). Post-cTBS, participants performed a sentence verification task on distorted (imprecisely articulated), and clear speech, whilst also undergoing stimulation of the lip representation in the left M1 to elicit motor evoked potentials (MEPs). In a second, separate experiment, we investigated the role of inter-hemispheric connectivity between right hemisphere PMv and left hemisphere M1 lip area. Dual-coil transcranial magnetic stimulation was applied to right PMv and left M1 lip in fifteen participants (aged 18–35). Results indicated that disruption of PMv during speech perception affects comprehension of distorted speech specifically. Furthermore, our data suggest that listening to distorted speech modulates the balance of intra- and inter-hemispheric interactions, with a larger sensorimotor network implicated during comprehension of distorted speech than when speech perception is optimal. The present results further understanding of PMv-M1 interactions during auditory-motor integration

The impact of age and psychosocial factors on cognitive and auditory outcomes during the COVID-19 pandemic

Purpose: In March 2020, the UK government announced that people should isolate to reduce the spread of the virus that causes COVID-19. Outside a pandemic, psychosocial factors, such as socialisation and mental health, may impact the relationship between hearing loss and increased dementia risk. We aim to report the impact of psychosocial factors, including social isolation, depression, and engagement in activities, on hearing and cognitive function in younger and older adults during the COVID-19 pandemic. Method: An online survey and experiment assessed self-reported psychosocial factors, self-reported hearing ability and speech-in-noise perception, and cognition. Data were collected between June 2020 and February 2021. Older (N = 112, MAGE = 70.08) and younger (N = 121, MAGE = 20.52) monolingual speakers of English, without any language or neurological disorders participated. Multiple linear regression models were employed to investigate hypothesised associations between psychosocial factors, and hearing and cognition, in older and younger adults. Results: Multiple regression analyses indicated that older adults displayed poorer speech-in-noise perception and poorer performance on one of four cognitive tasks, compared to younger adults; and increased depression was associated with poorer subjective hearing. Other psychosocial factors did not significantly predict hearing or cognitive function. Conclusions: Data suggest that self-reported hearing and depression are related. This conclusion is important for understanding the associations between hearing loss and cognitive decline in the long-term, as both hearing loss and depression are risk factors for dementia

The impact of age and psychosocial factors on cognitive and auditory outcomes during the COVID-19 pandemic

Purpose: In March 2020, the UK government announced that people should isolate to reduce the spread of the virus that causes COVID-19. Outside a pandemic, psychosocial factors, such as socialisation and mental health, may impact the relationship between hearing loss and increased dementia risk. We aim to report the impact of psychosocial factors, including social isolation, depression, and engagement in activities, on hearing and cognitive function in younger and older adults during the COVID-19 pandemic. Method: An online survey and experiment assessed self-reported psychosocial factors, self-reported hearing ability and speech-in-noise perception, and cognition. Data were collected between June 2020 and February 2021. Older (N = 112, MAGE = 70.08) and younger (N = 121, MAGE = 20.52) monolingual speakers of English, without any language or neurological disorders participated. Multiple linear regression models were employed to investigate hypothesised associations between psychosocial factors, and hearing and cognition, in older and younger adults. Results: Multiple regression analyses indicated that older adults displayed poorer speech-in-noise perception and poorer performance on one of four cognitive tasks, compared to younger adults; and increased depression was associated with poorer subjective hearing. Other psychosocial factors did not significantly predict hearing or cognitive function. Conclusions: Data suggest that self-reported hearing and depression are related. This conclusion is important for understanding the associations between hearing loss and cognitive decline in the long-term, as both hearing loss and depression are risk factors for dementia

The neural basis of authenticity recognition in laughter and crying

Deciding whether others’ emotions are genuine is essential for successful communication and social relationships. While previous fMRI studies suggested that differentiation between authentic and acted emotional expressions involves higher-order brain areas, the time course of authenticity discrimination is still unknown. To address this gap, we tested the impact of authenticity discrimination on event-related potentials (ERPs) related to emotion, motivational salience, and higher-order cognitive processing (N100, P200 and late positive complex, the LPC), using vocalised non-verbal expressions of sadness (crying) and happiness (laughter) in a 32-participant, within-subject study. Using a repeated measures 2-factor (authenticity, emotion) ANOVA, we show that N100’s amplitude was larger in response to authentic than acted vocalisations, particularly in cries, while P200’s was larger in response to acted vocalisations, particularly in laughs. We suggest these results point to two different mechanisms: (1) a larger N100 in response to authentic vocalisations is consistent with its link to emotional content and arousal (putatively larger amplitude for genuine emotional expressions); (2) a larger P200 in response to acted ones is in line with evidence relating it to motivational salience (putatively larger for ambiguous emotional expressions). Complementarily, a significant main effect of emotion was found on P200 and LPC amplitudes, in that the two were larger for laughs than cries, regardless of authenticity. Overall, we provide the first electroencephalographic examination of authenticity discrimination and propose that authenticity processing of others’ vocalisations is initiated early, along that of their emotional content or category, attesting for its evolutionary relevance for trust and bond formation