One of the main causes of aphasia is stroke

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In an article in Brain, researchers at the Medical University of South Carolina (MUSC) and elsewhere report which brain regions must be intact in stroke survivors with aphasia if they are to perform well in a speech entrainment session, successfully following along with another speaker.

Aphasia is the inability to speak, write or understand spoken or written language. One of the main causes of aphasia is stroke, the third leading cause of death in the U.S. About one in three stroke survivors develops aphasia.

Patients with non-fluent aphasia speak in short, halting, telegraphic sentences and have trouble forming their words. However, they often understand language relatively well.

“Speech entrainment is asking the person to repeat in real time what they hear and see, or in other words to copy the speech of another speaker,” said Leonardo Bonilha, M.D., Ph.D., who led the study. Bonilha is the SmartState Endowed Chair for Brain Imaging and an associate professor in the Department of Neurology at MUSC.

Bonilha and Janina Wilmskoelter, Ph.D., a postdoctoral fellow at MUSC, collaborated closely with Julius Fridriksson, Ph.D., professor in the Arnold School of Public Health at the University of South Carolina and director of the Center for the Study of Aphasia Recovery (C-STAR). Other team members include C-STAR collaborators from Johns Hopkins University and the University of California, Irvine.

Speech therapy can be effective in helping stroke survivors communicate better, but non-fluency is one of the hardest symptoms to treat.

Speech entrainment is an experimental approach for non-fluent aphasia in which stroke survivors practice speech production in real time by following along with another speaker.

However, not all patients with non-fluent aphasia can follow along with another speaker, suggesting that they might not benefit from speech entrainment therapy should it one day be approved for use in the clinic.

Before this study, researchers did not know why some stroke survivors could follow along with another speaker and others could not.

The multi-institutional team of aphasia researchers studied which brain structures were associated with successful speech entrainment.

They found that the left lateral temporal cortex needs to be intact for a stroke survivor to successfully follow along with another speaker.

“Our finding helps us understand better what are the neural mechanisms associated with the ability to have one’s speech entrained,” said Bonilha.

To assess performance in speech entrainment, the team calculated a speech entrainment score for forty-eight study participants with a history of stroke affecting the left side of the brain. The score was derived by comparing the number of words each patient produced per second during speech entrainment compared with spontaneous speech.

The investigators imaged the brain structures of the study participants using magnetic resonance imaging (MRI). They then used the MRI brain images to map the brain damage resulting from the stroke.

Next, the researchers turned to a form of artificial intelligence known as machine learning to find associations between speech entrainment scores and damaged brain areas.

They found that participants with damage to structures in the frontal and parietal lobes of the brain had impaired speech entrainment, confirming what scientists already knew.

But they also found something new.

“What was unknown were the brain areas that need to be intact for successful speech entrainment,” explained Bonilha. “We now have observed that the lateral temporal cortex needs to be there.”

In short, speech entrainment performance was better in those participants who had an intact lateral temporal cortex.

For their speech to be entrained, a patient needs to integrate sensory signals (what he or she hears and sees the speaker doing) with the motor part of speaking—producing speech through movement of the mouth, vocal cords and other structures.

The lateral temporal cortex may be a key brain area for this integration.

Bonilha and his collaborators were recently awarded a nearly $4.25 million grant from the National Institute on Deafness and Other Communication Disorders to conduct a clinical trial assessing the efficacy of speech entrainment for treatment of post-stroke aphasia. The findings of the Brain article will help inform that trial and provide a frame for interpreting its results.

The study will take place at MUSC, the University of South Carolina and the University of Utah. It will assess whether speech entrainment therapy improves the ability of patients with post-stroke aphasia to speak fluently and with less difficulty.

In addition, the researchers aim to determine how long speech entrainment therapy is necessary for maximal benefit.

“This upcoming clinical trial will determine the best dose and the effects of entrainment integrated into a new form of speech therapy,” said Bonilha. “It will be a very important first step for the development of a new and potentially transformative treatment for aphasia.”


Aphasia is a term used to describe a disturbance in the ability to use symbols (written or spoken) to communicate information and is categorized into two types: expressive aphasia or receptive aphasia.

These two types of aphasia can occur together.

This article discusses Broca’s aphasia (also called expressive aphasia). Broca’s aphasia was first described by the French physician Pierre Paul Broca in 1861. A mild form of this condition is termed dysphasia.

Aphasia/dysphasia should be distinguished from dysarthria which results from impaired articulation.

Dysarthria, as opposed to aphasia, is a motor dysfunction due to disrupted innervation to the face, tongue or soft palate that results in slurred speech but intact fluency and comprehension.

Aphasia is typically considered a cortical sign. Its presence suggests dysfunction of the dominant cerebral cortex.  [1][2][3]

Etiology

The most common cause of Broca’s aphasia is a stroke involving the dominant inferior frontal lobe or Broca’s area.

A stroke in Broca’s area is usually due to thrombus or emboli in the middle cerebellar artery or internal carotid artery.

Other causes of Broca’s aphasia include traumatic brain injury, tumors, and brain infections. Aphasia is a symptom of degenerative dementing illnesses such as Alzheimer disease. With dementing illness, patients develop gradual progressive language deficits as opposed to a sudden onset of loss of language function that is seen in an ischemic stroke.[4]

Epidemiology

Data on the incidence of Broca’s aphasia are limited. In the United States, approximately 170,000 new cases of aphasia related to stroke occur annually.[5]

Pathophysiology

Broca’s area is a region in the inferior frontal lobe of the dominant hemisphere of the brain made up of Brodmann area 44 and 45. Language function lateralized to the left hemisphere in 96% to 99% of right-handed people and 60% of left-handed people. Various pathways connect Broca’s area to the frontal lobe, basal ganglia, cerebellum, and contralateral hemisphere.

As a result of a lesion in Broca’s area, there is a breakdown between one’s thoughts and one’s language abilities.

Thus, patients often feel that they know what they wish to say but are unable to produce the words. That is, they are unable to translate their mental images and representations to words. This affects the normal fluency of speech. T

he loss of language function may be because Broca’s area serves a role in ordering sounds into words, and words into sentences, and thus creates relationships between linguistic elements.

History and Physical

Broca’s aphasia is non-fluent aphasia. The output of spontaneous speech is markedly diminished. There is a loss of normal grammatical structure (agrammatic speech). Specifically, small linking words, conjunctions (and, or, but) and the use of prepositions are lost. As an example, a sentence like “I took the dog for a walk.” may become “I walk dog.”

Patients can exhibit interjectional speech where there is a long latency, and the words that are expressed are produced as if under pressure. The ability to repeat phrases is also impaired. Despite these impairments, the words that are produced are often intelligible and contextually correct. In pure Broca’s aphasia, comprehension is intact. 

Patients with Broca’s aphasia are often very upset about their difficulty communicating. This may be due to the deficit itself or may be due to damage to adjacent frontal lobe structures which control the inhibition of negative emotions. Broca’s aphasia can accompany other neurological deficits such as right facial weakness, hemiparesis or hemiplegia, and apraxia.

Evaluation

Bedside examination of a patient with suspected aphasia includes assessments of fluency, the ability to name objects, repeat short phrases, follow simple and complex commands, read, and write. Formal neuropsychological testing may be helpful in determining the type and severity of the language deficit. Neuroimaging (CT, MRI, fMRI, PET or SPECT) may be required to localize and diagnose the cause of aphasia. Patients should also be screened for depression as this is also common in Broca’s aphasia. [6]

Treatment / Management

Broca’s aphasia often has a devastating effect on the ability of individuals to carry out their normal activities. It affects the patient’s ability to communicate and often leads to loss of productivity and vocation and can also lead to social isolation.[7][8][9]

Currently, there is no standard treatment for Broca’s aphasia. Treatments should be tailored to each patient’s needs. Speech and language therapy is the mainstay of care for patients with aphasia. It is essential to provide aphasic patients a means to communicate their wants and needs, so these may be addressed.

Often this is done by providing a board with various objects so that the patient can point to the object that they want.

Involvement of a speech therapist, neuropsychologist, and neurologist in the development of a care plan for the patient with Broca’s aphasia is very helpful in obtaining a good outcome.  One innovative treatment option for patients with Broca’s aphasia is melodic intonation. Melodic intonation relies on the fact that musical ability is often spared in Broca’s aphasia.

Thus, the speech therapist encourages the patient with poor speech production to try to express their words with musical tones. This approach has shown promise in clinical trials.

Medical treatment of aphasia is currently under investigation in clinical trials. Drug therapies have included catecholaminergic agents (bromocriptine, levodopa, amantadine, dexamphetamine), piracetam and related compounds, acetylcholine esterase inhibitors, and neurotrophic factors. Previous studies have been small, and further studies are needed to determine the efficacy of these pharmacological agents. Also, transcranial magnetic stimulation and transcranial direct stimulation trials for aphasia are currently underway.

When the cause of Broca’s aphasia is a stroke, recovery of language function peaks within two to six months, after which time further progress is limited. However, patients should be encouraged to work on speech production, because cases of improvement have been seen long after a stroke. There are commercial software products available that claim to improve language function, but for the most part, these have not been rigorously tested in randomized clinical trials. 

It is important to address issues of post-stroke depression and post-stroke cognitive impairment, as well as disorders of executive function, awareness, neglect, and hemiparesis during the rehabilitation process to optimize the outcome for an individual patient. Family and social support are extremely important to keep patients with language deficits engaged in social and leisure activities which can greatly influence the aphasic patient’s quality of life.

Pearls and Other Issues

When speaking to a patient with aphasia, it is important to maintain a normal rate and volume. Questions should be simple. It is preferable to ask yes or no questions rather than open-ended questions that require a lengthy answer.

Enhancing Healthcare Team Outcomes

Broca’s aphasia is often seen in patient’s with head trauma or a stroke. While the individual has preserved comprehension, they have trouble speaking fluently. These patients often undergo speech therapy but because of their other illnesses are often looked after by nurses. Hence, nurses need to be aware of this speech disorder. Individuals with this disorder may be able to read, but their writing ability may be limited.

However, it is important to appreciate the fact that in Broca’s aphasia, there is a preservation of intellectual and cognitive functions. [10][6]

Some patients may recover functionally and be able to lead an independent life as long as they do not have other comorbidities or neurological deficits. The recovery after Broca’s aphasia is often many months or even years, especially if the cause was a stroke. Most people see mild improvement within the first six months, but full recovery can take years. The key is to educate the family members of caregivers who will be looking after the patients.[11]


More information: Leonardo Bonilha et al, Neural structures supporting spontaneous and assisted (entrained) speech fluency, Brain (2019). DOI: 10.1093/brain/awz309

Journal information: Brain
Provided by Medical University of South Carolina

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