The dual-stream model of speech processing describes a cortical network involved in speech processing. However, it is not yet known if the dual-stream model represents actual intrinsic functional brain networks. Furthermore, it is unclear how disruptions after a stroke to the functional connectivity of the dual-stream model's regions are related to speech production and comprehension impairments seen in aphasia. To address these questions, in the present study, we examined two independent resting-state fMRI data sets: (1) 28 neurotypical matched controls and (2) 28 chronic left-hemisphere stroke survivors collected at another site. We successfully identified an intrinsic functional network among the dual-stream model's regions in the control group using functional connectivity. We then used both standard functional connectivity analyses and graph theory approaches to determine how this connectivity may predict performance on clinical aphasia assessments. Our findings provide evidence that the dual-stream model of speech processing is an intrinsic network as measured via resting-state MRI and that functional connectivity of the hub nodes of the dual-stream network defined by graph theory methods, but not overall average network connectivity, is weaker in the stroke group than in the control participants. In addition, the functional connectivity of the hub nodes predicted linguistic impairments on clinical assessments. In particular, the relative strength of connectivity of the right hemisphere's homologues of the left dorsal stream hubs to the left dorsal hubs, versus to the right ventral stream hubs, is a particularly strong predictor of poststroke aphasia severity and symptomology.

We investigated the ability of 40 left-hemisphere brain-lesioned individuals with various diagnoses of aphasia to temporally synchronize the audio of a spoken word to its congruent video using a maximum-likelihood adaptive psychophysical procedure. We found a statistically significant effect of aphasia type, not explained by lesion volume, on measures of audiovisual (AV) synchrony. Brain-lesioned individuals with no symptoms of aphasia, and those with conduction aphasia performed on the synchrony task more similarly to age-matched neurotypical controls, whereas those with anomic aphasia performed the poorest. In addition, we examined the correlation between this ability and AV integration (fusion) and observed a significant correlation between measures of AV synchrony and fusion. An ROI analysis of stroke lesion maps showed that damage to the left posterior temporal regions adversely affected AV processing, although whole-brain univariate lesion-symptom mapping analyses did not yield any significant results. These findings contribute to a better understanding of the functional relationship between different AV processes in multimodal integration and their underlying cortical networks in the human brain.