However, the neural mechanisms underlying the phenomenon have so far remained unknown.
A study conducted at the University of Helsinki and the Turku University Hospital Neurocenter compared the effect of listening to vocal music, instrumental music and audiobooks on the structural and functional recovery of the language network of patients who had suffered an acute stroke.
In addition, the study investigated the links between such changes and language recovery during a three-month follow-up period.
The study was published in the eNeuro journal.
Based on the findings, listening to vocal music improved the recovery of the structural connectivity of the language network in the left frontal lobe compared to listening to audiobooks. These structural changes correlated with the recovery of language skills.
“For the first time, we were able to demonstrate that the positive effects of vocal music are related to the structural and functional plasticity of the language network. This expands our understanding of the mechanisms of action of music-based neurological rehabilitation methods,” says Postdoctoral Researcher Aleksi Sihvonen.
Listening to music supports other rehabilitation
Aphasia, a language impairment resulting from a stroke, causes considerable suffering to patients and their families. Current therapies help in the rehabilitation of language impairments, but the results vary and the necessary rehabilitation is often not available to a sufficient degree and early enough.
“Listening to vocal music can be considered a measure that enhances conventional forms of rehabilitation in healthcare. Such activity can be easily, safely and efficiently arranged even in the early stages of rehabilitation,” Sihvonen says.
According to Sihvonen, listening to music could be used as a cost-efficient boost to normal rehabilitation, or for rehabilitating patients with mild speech disorders when other rehabilitation options are scarce.
After a disturbance of the cerebral circulation, the brain needs stimulation to recover as well as possible. This is the goal of conventional rehabilitation methods as well.
“Unfortunately, a lot of the time spent in hospital is not stimulating. At these times, listening to music could serve as an additional and sensible rehabilitation measure that can have a positive effect on recovery, improving the prognosis,” Sihvonen adds.
During the last decade, there has been growing interest toward music as a neurorehabilitation tool, especially for stroke. 1 This has been fueled by (1) the rapidly increasing prevalence of stroke and its massive socioeconomic burden and growing need for cost‐effective rehabilitation tools 2 and (2) advances in music neuroscience, uncovering the wide‐spread cortical and subcortical networks underlying the auditory, motor, cognitive, and emotional processing of music 3 , 4 and their malleability by musical training. 5
In the rehabilitation context, music can be viewed as a form of environmental enrichment (EE) that increases activity‐dependent neuroplasticity in the large‐scale brain network it stimulates. 6 In animals, EE is a powerful driver of synaptic plasticity, neurotrophin production, and neurogenesis, improving also cognitive‐motor recovery. 7
In stroke patients, EE where patients are provided additional social interaction and stimulating activities (e.g., games) is emerging as a promising way to increase physical, social, and cognitive activity. 8
Previously, we explored the long‐term efficacy of musical EE in a three‐arm randomized controlled trial (RCT) comparing daily music listening to a control intervention (audiobook listening) and standard care (SC) in stroke patients. Music listening enhanced the recovery of verbal memory and attention and reduced negative mood 9 as well as increased gray matter volume (GMV) in spared prefrontal and limbic areas in left hemisphere‐lesioned patients. 10
Corroborating results were recently obtained in another RCT where daily music listening, alone or in combination with mindfulness training, enhanced verbal memory and attention more than audiobooks. 11 While these results imply that music listening can be cognitively, emotionally, and neurally effective after stroke, its tailored, more optimized use in stroke rehabilitation requires determining which components of music are specifically driving these effects and which patients benefit most from it.
The vocal (sung) component of music could be one key factor contributing to its rehabilitative efficacy. Singing is one of the oldest forms of human communication, a likely precursor to language evolution. 12 Songs represent an important interface between speech and music, binding lyrics and melody into a unified representation and engaging linguistic and vocal‐motor brain processes in addition to the auditory, cognitive, and emotional processing associated with instrumental music. fMRI evidence indicates that listening to sung music activates temporal, frontal, and limbic areas more bilaterally and extensively than listening to speech 13 , 14 or instrumental music, 15 , 16 also in the early poststroke stage. 17
After unilateral stroke, spared brain regions in both ipsi‐ and contralesional hemisphere undergo spontaneous neuroplasticity changes and steer the recovery of behavioral functions, including speech. 18 In this regard, the large‐scale bilateral activation induced by vocal music could make it more effective than speech or instrumental music that engage primarily the left or right hemisphere, respectively. 19
Vocal music is particularly interesting in the domain of aphasia rehabilitation. In nonfluent aphasia, the ability to retain the ability to produce words through singing is often preserved, and aphasic patients are also able to learn new verbal material when utilizing a sung auditory model. 20
Singing‐based speech training interventions, such as melodic intonation therapy (MIT), have been found effective in enhancing the production of trained speech content and the recovery of verbal communication in aphasia, especially when provided at the subacute poststroke stage. 21 , 22 Whether regular listening to vocal music could have long‐term positive effects on early language recovery in aphasia is currently unknown.
In the present study, we use data pooled from two RCTs (N = 83), including our previous trial 9 , 10 (N = 38) and a new, previously unpublished trial (N = 45), to (1) determine the contribution of sung lyrics on the cognitive, linguistic, and emotional efficacy of music by comparing daily listening to vocal music, instrumental music, and audiobooks and (2) uncover the structural neuroplasticity (GMV) and functional connectivity (FC) changes underlying them.
We hypothesized that
(i) vocal music would be superior to instrumental music and audiobooks in enhancing cognitive and language recovery,
(ii) both vocal and instrumental music would enhance mood more than audiobooks, and
(iii) the rehabilitative effects of vocal music would be linked to GMV changes in temporal, frontal, and parietal regions associated with the processing of language, music, and memory 13 , 14 , 15 , 16 , 17 and commonly induced by musical training 5 as well as increased resting‐state functional connectivity (FC), particularly in the default mode network (DMN), 23 which has recently been linked to stroke recovery. 24 , 25
Moreover, given previous evidence on singing‐based speech rehabilitation in aphasia, 21 , 22 we (3) explore whether listening to vocal music can be effective for aphasia recovery.
Discussion
The present study set out to verify and extend previous results on beneficial effects of daily music listening on cognitive, emotional, and neural recovery after stroke 9 , 10 , 11 and to explore whether the vocal (sung) component of music plays a key role in its rehabilitative efficacy. Specifically, we pooled data from two single‐blind parallel‐group RCTs of stroke patients (total N = 83), comprising our previous trial 9 , 10 (N = 38) and a new trial (N = 45), which both had a 6‐month follow‐up and utilized a combination of cognitive, emotional, and neuroimaging outcome measures.
Our main findings were that compared to audiobooks vocal music listening enhanced the recovery of verbal memory and language. An exploratory post hoc subgroup analysis suggested that especially aphasic patients may benefit from listening to vocal music as a means to facilitate early language recovery.
These positive effects of vocal music listening were coupled with increased structural neuroplasticity, indicated by GMV/WMV changes, in left temporal areas in all patients and in right medial parietal areas in aphasics and with functional neuroplasticity, indicated by resting‐state and task‐related FC increases in the DMN.
The specific enhancement of language and verbal memory induced by vocal music suggests that the sung (vocal) component of music listening is crucial for its rehabilitative effect. Conceptually, songs represent an interface between speech and music, binding together lyrics and melody and providing a structured temporal scaffolding framework that facilitates their recall.
The close coupling of vocal music and verbal memory is evidenced by behavioral studies of stroke patients showing that (1) verbal material (stories) is learned and recalled better when presented in sung than spoken format 33 and (2) overt production of verbal material during memory encoding is more effective for later recall when done through singing than speaking. 20
Even though VMG patients were not instructed to sing along to the songs, it is plausible that listening to the songs may have elicited subvocal processing, which could have covertly trained the phonological loop function of working memory, leading to an enhanced verbal memory recovery. Subvocal training could also underlie the enhancement of language skills induced by the vocal music listening, especially in aphasic patients, as singing‐based rehabilitation has been found effective for speech in aphasia. 21 , 22
Vocal music can also enhance vigilance or arousal, 34 which is likely mediated by emotional factors. Music evokes strong emotions and induces pleasure and rewarding experiences which arise from increased activation of the mesolimbic reward system 4 , 35 in which dopamine plays a causal role. 36
Given that music‐induced pleasure and engagement of the limbic network are higher when listening to familiar versus unfamiliar music 37 and sung versus instrumental music 15 , 16 and that the individual reward value of music mediates its positive effect on episodic memory, 38 it is possible that the observed positive effect of vocal music on verbal memory recovery is at least partly driven by its intrinsic ability to engage motivation‐ and reward‐related dopaminergic networks.
Although music listening has a general mood‐enhancing and stress‐reducing effect in daily life, 39 the effects of music listening on poststroke mood, as measured by POMS, were not significant in the present study when compared to audiobook listening (as shown in Table 4, there was a slight trend for reduced Depression and Confusion in the music groups compared to the ABG at T1, but the group effect did not reach significance).
Given also our previous results where the positive effects of music listening on POMS Depression and Confusion were seen only when compared to the standard care control group 9 as well as the results of Baylan et al. 11 where the effects of music and audiobook listening did not differ on another clinical mood scale (Hospital Anxiety and Depression Scale), the impact of daily music listening for enhancing mood after stroke is still unclear, at least when compared to another stimulating recreational activity.
Our previous exploratory VBM findings indicated that in left hemisphere‐lesioned stroke patients (N = 23), music listening increased GMV in left and right superior frontal gyrus, left anterior cingulate, and right ventral striatum compared to audiobooks and standard care. 10 Using a larger sample (N = 75) and more rigorous statistical criteria (FWE‐correction), the present results showed that compared to audiobooks, vocal music listening specifically increased GMV in left temporal areas (STG, MTG, ITG) areas across all patients.
Stronger activation in left temporal regions has been reported in previous fMRI studies of healthy subjects comparing song and speech listening. 13 , 14 These regions also play a crucial role in perceiving the spectrotemporal structure of sounds 40 as well as in the combinatorial processing of lexical, phonological, and articulatory features of speech 41 and also in verbal working memory. 42 , 43
In aphasic patients, increased GMV/WMV induced by vocal or instrumental music listening was seen in right medial parieto‐occipital areas (LG, cuneus, MOG) and in posterior temporal (MTG) areas, which have been linked to music and speech perception 44 and memory‐related visual imagery. 45
Importantly, the volume changes in these posterior temporal and parietal regions correlated with enhanced recovery of language and verbal memory, which is in line with previously reported therapy‐induced changes in aphasia in these regions. 46 Notably, the VMG > ABG effects were partly driven by a reduction of GMV in ABG in these clusters.
After stroke, spared brain regions can show both volume increase, which indicates recovery‐related neuroplasticity, and volume decrease, which indicates atrophy and is associated with poor recovery and lower gains induced by rehabilitation. 47 It is possible that the large‐scale neural activation induced by music listening after stroke 17 can have a long‐term neuroprotective impact by preventing atrophy in cortical areas most strongly activated by songs.
Music listening induced also long‐term FC changes in the DMN. As the DNM is linked to emotional processing, self‐referential mental activity, and the recollection of prior experiences, 23 it is strongly engaged also when listening to music, especially when it is familiar and self‐preferred. 48
In line with this, VMG showed larger increase in FC in the whole DMN during vocal music (but not instrumental music or speech) listening than ABG, indicating functional neuroplasticity specific to the type of stimulus and intervention. Importantly, also resting‐state FC in the left temporal (STG/MTG) areas of the DMN increased more in VMG than in ABG or IMG, and correlated with the improved recovery of language and verbal memory.
Previously, reduced DMN connectivity has been associated with verbal memory impairment in aging 32 and after stroke 49 and increased DMN connectivity with successful stroke recovery. 25 Together, the VBM and FC results provide compelling evidence that the rehabilitative effect of vocal music is underpinned by both structural and functional plasticity changes in temporoparietal networks crucial for emotional processing, language, and memory.
The present study has some methodological limitations, which should be taken into account when evaluating its findings. First of all, the study was not a single RCT but a pooled analysis of two RCTs, one with randomization to three (VMG/IMG/ABG) groups (Turku) and the other with randomization to two groups (MG/ABG) and then post hoc reclassification to three (VMG/IMG/ABG) groups (Helsinki).
The results may therefore include a slight self‐selection bias, more so between the two music groups and less so between the music groups and the ABG. However, given that the study design of the two trials was otherwise highly similar and that all outcome measure results were covaried for trial site, we do not feel that this represents a significant bias.
Regarding power, due to the combined sample size of the two studies, the pooled analysis had greater test power than each of the individual studies. Using G*Power, we performed a post hoc calculation of the achieved power based on the effect sizes of the original Helsinki study. 9
This showed that the pooled sample yielded 97% power for the primary outcome (verbal memory) and 76%–87% power for the secondary outcomes (language skills, focused attention, POMS Depression, POMS Confusion) to detect a significant change between groups from T0 to T1, suggesting that the study was sufficiently powered.
The effect sizes (ηp2) in the present study for the efficacy of music listening on verbal memory and language recovery were of medium level, reaching a large level for the efficacy of vocal music listening on language recovery in aphasics. Second, owing to the relatively small sample sizes in the subgroup analyses of aphasic patients (N = 29) and in the fMRI analyses (N = 35), their results should be considered still somewhat tentative and need to be confirmed with larger studies.
Especially studies of aphasic patients with more varying severity levels and aphasia subtypes are warranted. Also uncovering if and how different demographic and clinical background factors, such as prestroke music listening and amusia which were included as covariates in the analyses, mediate the efficacy of music listening need to be explored in a larger trial, as this could pave the way toward more individualized use of music listening in stroke rehabilitation.
Clinically, the findings address a vital issue of how the patient environment can be optimized for recovery during the first weeks after stroke when typically over 70% of daily time is spent in nontherapeutic activities 50 even though this time‐window is ideal for rehabilitation from the standpoint of neuroplasticity. Corroborating previous findings, 9 , 10 , 11 the present study provides further evidence for the use of music listening as an effective, easily applicable, and inexpensive way to support cognitive recovery after stroke.
Importantly, our results show for the first time that the vocal (sung) component of music is driving its rehabilitative effect on verbal memory and that vocal music can also speed up language recovery in aphasia during the first 3 months. The reason why the positive effect of vocal music occurs particularly at the early poststroke stage is likely linked to the dynamic pattern of language reorganization in aphasia, where upregulation of both left and right frontotemporal regions takes place at the early (first weeks and months) recovery stage, followed by more pronounced reorganization of perilesional left regions at the chronic (6‐month) stage. 18
It is plausible that vocal music engages and stimulates the bilateral frontotemporal network more extensively than audiobooks, leading to a better language recovery in aphasia at the early stage, whereas the effects begin to level off at the chronic stage when left hemisphere mechanisms (engaged more evenly by vocal music and audiobooks) become more dominant.
Although more research is still needed to verify the effects of vocal music listening on aphasia, our novel findings suggest that it could perhaps be used to supplement speech therapy, which is often difficult to implement at the early poststroke stage due to severity of symptoms, general fatigue, and lack of rehabilitation resources.
reference link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7664275/
Original Research: Open access.
“Vocal Music Listening Enhances Poststroke Language Network Reorganization” by Aleksi J. Sihvonen, Pablo Ripollés, Vera Leo, Jani Saunavaara, Riitta Parkkola, Antoni Rodríguez-Fornells, Seppo Soinila and Teppo Särkämö. eNeuro
