The Role of the Left Temporal Lobe in Naming and Semantic Knowledge

Abstract

Background: Anomia is often demonstrated by individuals who sustain damage to the left inferior temporal lobe. The nature of the anomia in individuals with damage to anterior regions of the left temporal lobe (BA 38, 21, 20) has been associated with degradation to semantic knowledge (semantic anomia), while damage to regions farther posterior (BA 37) has been associated with disconnection between preserved semantic knowledge and access to phonological word forms (pure anomia). However, evidence of semantic anomia often comes from individuals with cortical damage that extends beyond left temporal regions, so that it remains unclear whether unilateral damage to this area will result in semantic degradation. Aims: The aim of this study was to examine naming performance in individuals with focal damage to anterior versus posterior regions of the left inferior temporal lobe to determine whether there is a difference in the nature of the observed anomia. Methods: Eight individuals who underwent left anterior temporal lobectomy (L ATL) and eight individuals who sustained left posterior cerebral artery infarcts (L PCA) completed a battery of language measures that assessed lexical retrieval and semantic processing. Sixteen age-and-education matched controls also completed this battery. High resolution structural brain scans were collected for each individual who sustained brain damage. Performance on behavioral measures was examined relative to lesion size and location using statistical analyses. Results: Naming performance ranged from severely impaired to unimpaired in both groups of brain damaged individuals. Both the L ATL and L PCA groups demonstrated well preserved semantic knowledge during lexical retrieval tasks and assessments of semantic knowledge. Naming performance was correlated with lesion volume. Furthermore, a relationship between percent damage to inferior temporal regions, BAs 20 and 21, and naming performance was observed. Conclusion: The behavioral and neuroanatomical evidence indicated that individuals with unilateral damage to left inferior temporal cortex, regardless of anterior versus posterior lesion location, do not demonstrate semantic anomia. These findings suggest that, even in the presence of severe naming impairment, unilateral damage to left inferior temporal cortex is not sufficient to significantly degrade semantic knowledge.