  Aphasia is a speech-language impairment commonly caused by damage to the left
hemisphere. Due to the complexity of speech-language processing, the neural
mechanisms that underpin various symptoms between different types of aphasia
are still not fully understood. We used the network-based statistic method to
identify distinct subnetwork(s) of connections differentiating the
resting-state functional networks of the anomic and Broca groups. We identified
one such subnetwork that mainly involved the brain regions in the premotor,
primary motor, primary auditory, and primary sensory cortices in both
hemispheres. The majority of connections in the subnetwork were weaker in the
Broca group than the anomic group. The network properties of the subnetwork
were examined through complex network measures, which indicated that the
regions in the superior temporal gyrus and auditory cortex bilaterally exhibit
intensive interaction, and primary motor, premotor and primary sensory cortices
in the left hemisphere play an important role in information flow and overall
communication efficiency. These findings underlied articulatory difficulties
and reduced repetition performance in Broca aphasia, which are rarely observed
in anomic aphasia. This research provides novel findings into the resting-state
brain network differences between groups of individuals with anomic and Broca
aphasia. We identified a subnetwork of, rather than isolated, connections that
statistically differentiate the resting-state brain networks of the two groups,
in comparison with standard lesion symptom mapping results that yield isolated
connections.
