Brain Connectivity Supporting Language Recovery in Aphasia

Aphasia, an impairment of language processing, is one of the most common consequences of strokes affecting the dominant brain hemisphere4. Patients with aphasia are usually incapable of working, and their interactions with family and friends are often severely affected. The hallmark deficit of aphasia is the inability to name objects or people (anomia)12. The severity of anomia is closely related to a poor quality of life.

While many patients with aphasia exhibit some language recovery in the first days to weeks after the stroke, 30-40% persist with long lasting naming impairments4. Fortunately, speech therapy can be very effective to improve naming for some patients with chronic aphasia5-8. However, it is well recognized among clinicians that speech therapy can be ineffective for other patients, making it difficult to predict how and why some patients benefit from naming treatment, while others show little or no improvement.

Here, the investigators propose to evaluate whether naming impairment and naming recovery are related to the extent of structural damage to the cortical language network. Importantly, the investigators will evaluate damage as the combined effect of cortical necrosis and cortical disconnection. The investigators hypothesize that assessing anomia as being either due to gray matter necrosis or due to cortical disconnection constitutes a false dichotomy since most chronic patients exhibit gray and white matter damage. Furthermore, the investigators propose that disconnection of seemingly spared cortical areas has up till now been underappreciated in patients with stroke due to limitations in brain connectivity assessment tools. By examining only areas of cortical necrosis without considering disconnected areas, one may underestimate the magnitude of language network damage. A better understanding of the effects from both cortical damage and disconnection on anomia and its recovery could lead to an improved clinical management of aphasia.

The investigators will employ the innovative concept of the brain connectome, i.e., the individualized map of neural connections in the brain, to evaluate whether naming recovery is supported by preserved gray matter and preserved connectivity involving key language areas in the left hemisphere. The investigators propose that left frontal and left temporal connectivity mapped based on the individual's connectome is an important explanatory variable towards naming impairment and recovery.

The investigators believe that this research is significant for the three main reasons. First, it can have a direct clinical impact by providing a better understanding of which patients can benefit from therapy. Second, it can unveil the neurobiological mechanisms supporting language recovery, improving our understanding of brain plasticity related to language rehabilitation. Finally, if disconnection contributes to language impairment, our methods can be developed to test specific theories of language organization in the brain. The significance of these aspects is explained in detail below.