Mechanisms and anatomy of unilateral extinction after brain injury

Unilateral extinction is a common consequence of unilateral brain injury in which individuals fail to detect a contralesional target when presented together with a competing ipsilesional target. Here we review the literature on the different mechanisms and anatomy hypothesized to underlie unilateral extinction. We argue that extinction, which reflects a specific deficit in the simultaneous processing of multiple briefly presented targets, should be distinguished from the failure to actively explore and serially detect targets amongst distractors in contralesional space commonly known as spatial neglect. While contralesional sensory defects can be correlated with extinction, these sensory impairments alone are usually not sufficient to explain the deficit. Prototypical extinction is instead best seen as the result of a pathologically biased competition between multiple target representations for pathologically limited attentional resources. The temporo-parietal junction (TPJ) is a critical site in many of the lesions that provoke extinction. Additionally, the intraparietal sulcus (IPS) may play a role in modulation of competitive interactions between multiple target representations.