The function of the left anterior temporal pole: evidence from acute stroke and infarct volume

Abstract

The role of the anterior temporal lobes in cognition and language has been much debated in the literature over the last few years. Most prevailing theories argue for an important role of the anterior temporal lobe as a semantic hub or a place for the representation of unique entities such as proper names of peoples and places. Lately, a few studies have investigated the role of the most anterior part of the left anterior temporal lobe, the left temporal pole in particular, and argued that the left anterior temporal pole is the area responsible for mapping meaning on to sound through evidence from tasks such as object naming. However, another recent study indicates that bilateral anterior temporal damage is required to cause a clinically significant semantic impairment. In the present study, we tested these hypotheses by evaluating patients with acute stroke before reorganization of structure-function relationships. We compared a group of 20 patients with acute stroke with anterior temporal pole damage to a group of 28 without anterior temporal pole damage matched for infarct volume. We calculated the average percent error in auditory comprehension and naming tasks as a function of infarct volume using a non-parametric regression method. We found that infarct volume was the only predictive variable in the production of semantic errors in both auditory comprehension and object naming tasks. This finding favours the hypothesis that left unilateral anterior temporal pole lesions, even acutely, are unlikely to cause significant deficits in mapping meaning to sound by themselves, although they contribute to networks underlying both naming and comprehension of objects. Therefore, the anterior temporal lobe may be a semantic hub for object meaning, but its role must be represented bilaterally and perhaps redundantly.

Figure 1

Errors (dots) for each patient and average errors (regression lines) as a function of log(10) infarct volume in ATL (blue) and no ATL (red) groups for naming.

Figure 2

Errors (dots) for each patient and average errors (regression lines) as a function of log(10) infarct volume in ATL (blue) and no ATL (red) groups for auditory comprehension.

Figure 3

MRI of a patient with very impaired comprehension and naming performance whose lesion spared the left temporal pole.

Figure 4

MRI of a patient with very impaired comprehension and naming. performance whose lesion included the left temporal pole as we defined it (including the anterior tip of Brodmann area 22).