Entrainment is defined by a temporal locking process in which one system’s motion or signal frequency entrains the frequency of another system. This process is a universal phenomenon that can be observed in physical (e.g., pendulum clocks) and biological systems (e.g. fire flies). However, entrainment can also be observed between human sensory and motor systems. The function of rhythmic entrainment in rehabilitative training and learning was established for the first time by Thaut and colleagues in several research studies in the early 1990s. It was shown that the inherent periodicity of auditory rhythmic patterns could entrain movement patterns in patients with movement disorders (see for a review: Thaut et al, 1999). Physiological, kinematic and behavioral movement analysis showed very quickly that entrainment cues not only changed the timing of movement but also improved spatial and force parameters. Mathematical models have shown that anticipatory rhythmic templates as critical time constraints can result in the complete specification of the dynamics of a movement over the entire movement cycle, thereby optimizing motor planning and execution. Furthermore, temporal rhythmic entrainment has been successfully extended into applications in cognitive rehabilitation and speech and language rehabilitation, and thus become one of the major neurological mechanisms linking music and rhythm to brain rehabilitation. These findings provided a scientific basis for the development of Neurologic Music Therapy.

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Neurobiological foundations of neurologic music therapy: rhythmic entrainment and the motor system.

A classic observation in neurology is that aphasics can sing words they cannot pronounce otherwise. To further assess this claim, we investigated the production of sung and spoken utterances in eight brain-damaged patients suffering from a variety of speech disorders as a consequence of a left-hemisphere lesion. In Experiment 1, the patients were tested in the repetition and recall of words and notes of familiar material. Lyrics of familiar songs, as well as words of proverbs and prayers, were not better pronounced in singing than in speaking. Notes were better produced than words. In Experiment 2, the aphasic patients repeated and recalled lyrics from novel songs. Again, they did not produce more words in singing than in speaking. In Experiment 3, when allowed to sing or speak along with an auditory model while learning novel songs, aphasics repeated and recalled more words when singing than when speaking. Reduced speed or shadowing cannot account for this advantage of singing along over speaking in unison. The results suggest that singing in synchrony with an auditory model--choral singing--is more effective than choral speech, at least in French, in improving word intelligibility because choral singing may entrain more than one auditory-vocal interface. Thus, choral singing appears to be an effective means of speech therapy.

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Making non-fluent aphasics speak: sing along!

MUSIC MAKING (PLAYING AN INSTRUMENT OR SINGING) is a multimodal activity that involves the integration of auditory and sensorimotor processes. The ability to sing in humans is evident from infancy, and does not depend on formal vocal training but can be enhanced by training. Given the behavioral similarities between singing and speaking, as well as the shared and distinct neural correlates of both, researchers have begun to examine whether singing can be used to treat some of the speech-motor abnormalities associated with various neurological conditions. This paper reviews recent evidence on the therapeutic effects of singing, and how it can potentially ameliorate some of the speech deficits associated with conditions such as stuttering, Parkinson9s disease, acquired brain lesions, and autism. By reviewing the status quo, it is hoped that future research can help to disentangle the relative contribution of factors to why singing works. This may ultimately lead to the development of specialized or "gold-standard" treatments for these disorders, and to an improvement in the quality of life for patients.

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The Therapeutic Effects of Singing in Neurological Disorders

The question of whether singing may be helpful for stroke patients with non-fluent aphasia has been debated for many years. However, the role of rhythm in speech recovery appears to have been neglected. In the current lesion study, we aimed to assess the relative importance of melody and rhythm for speech production in 17 non-fluent aphasics. Furthermore, we systematically alternated the lyrics to test for the influence of long-term memory and preserved motor automaticity in formulaic expressions. We controlled for vocal frequency variability, pitch accuracy, rhythmicity, syllable duration, phonetic complexity and other relevant factors, such as learning effects or the acoustic setting. Contrary to some opinion, our data suggest that singing may not be decisive for speech production in non-fluent aphasics. Instead, our results indicate that rhythm may be crucial, particularly for patients with lesions including the basal ganglia. Among the patients we studied, basal ganglia lesions accounted for more than 50% of the variance related to rhythmicity. Our findings therefore suggest that benefits typically attributed to melodic intoning in the past could actually have their roots in rhythm. Moreover, our data indicate that lyric production in non-fluent aphasics may be strongly mediated by long-term memory and motor automaticity, irrespective of whether lyrics are sung or spoken.

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Rhythm in disguise: Why singing may not hold the key to recovery from aphasia

Summary We investigated the production of sung and spoken utterances in a non-fluent patient, C.C., who had a severe expressive aphasia following a right-hemisphere stroke, but whose language comprehension and memory were relatively preserved. In experiment 1, C.C. repeated familiar song excerpts under four different conditions: spoken lyrics, sung lyrics on original melody, lyrics sung on new but familiar melody and melody sung to a neutral syllable ‘la’. In experiment 2, C.C. repeated novel song excerpts under three different conditions: spoken lyrics, sung lyrics and sung-to-la melody. The mean number of words produced under the spoken and sung conditions did not differ significantly in either experiment. The mean number of notes produced was not different either in the sung-to-la and sung conditions, but was higher than the words produced, hence showing a dissociation between C.C.’s musical and verbal productions. Therefore, our findings do not support the claim that singing helps word production in non-fluent aphasic patients. Rather, they are consistent with the idea that verbal production, be it sung or spoken, result from the operation of same mechanisms.

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Revisiting the dissociation between singing and speaking in expressive aphasia.

Metronome, singing, and board pacing were used as external rate control techniques for the purpose of comparing the effectiveness of auditory and visual speech timing cues for reducing speech rate and increasing intelligibility in three traumatically brain injured mixed spastic-ataxic dysarthric speakers. A single system design with baseline reversal (ABACAD) was used in this preliminary investigation. Results demonstrated statistically significant (p < 0.05) changes in increased speech intelligibility during all three pacing conditions for the two more involved subjects. Differences between treatment conditions were not statistically significant. However, auditory metronome cuing showed the best results for the two subjects who benefited from rate control. Lower baseline intelligibility was strongly correlated with higher benefit from rate control. Furthermore, the two auditory rhythmic pacing conditions exhibited a close synthronization effect between the frequency rate of the cue and speech rate. Significant correlation coefficients between decreased speech rate and increased intelligibility were only found for the two more involved subjects. These findings suggested a differential benefit of slowing speech rate to improve intelligibility contingent upon severity of speech deficits.

Auditory vs visual speech timing cues as external rate control to enhance verbal intelligibility in mixed spastic ataxic dysarthric speakers: a pilot study

Marcella A. Pilon

Papers

Auditory vs visual speech timing cues as external rate control to enhance verbal intelligibility in mixed spastic ataxic dysarthric speakers: a pilot study