  Damage to the white matter underlying the left posterior temporal lobe leads
to deficits in multiple language functions. The posterior temporal white matter
may correspond to a bottleneck where both dorsal and ventral language pathways
are vulnerable to simultaneous damage. Damage to a second putative white matter
bottleneck in the left deep prefrontal white matter involving projections
associated with ventral language pathways and thalamo-cortical projections has
recently been proposed as a source of semantic deficits after stroke. However,
the effects of damage to a priori identified white matter bottlenecks on
language function have not been directly investigated. Here, we first used
white matter atlases to identify the previously described white matter
bottlenecks in the posterior temporal and deep prefrontal white matter. We then
assessed the effects of damage to each region on measures of category fluency,
picture naming, and auditory semantic decision-making in 43 patients with
chronic aphasia. Damage to the posterior temporal bottleneck predicted deficits
on all language measures, while damage to the anterior bottleneck only
predicted deficits in category fluency. Importantly, the effects of damage to
the bottleneck regions were not attributable to lesion volume, lesion loads on
the tracts traversing the bottlenecks, or damage to nearby cortical language
areas. Multivariate lesion-symptom mapping and fiber tracking analyses
corroborated these findings. Together, our results provide strong support for
the proposal that spatially specific white matter damage affecting white matter
bottlenecks, particularly in the posterior temporal lobe, contribute to chronic
language deficits after left hemispheric stroke. Our results suggest that
damage to this area is likely to simultaneously disrupt signaling via the
simultaneous disruption of dorsal and ventral language processing streams.
