Category-Specific Semantic Impairment After Left Anterior Thalamic Infarction: A Case Report.

Thalamic lesions can result in a wide range of higher-order cognitive deficits; however, their association with category-specific semantic impairment has not been sufficiently examined. We report a 41-year-old man with a left anterior thalamic infarction who exhibited fluent speech with preserved repetition but showed asymmetric performance declines across semantic categories in both noun comprehension and naming, particularly under low-familiarity conditions. Detailed assessment revealed category-specific semantic impairment characterized by an interaction between semantic category and item familiarity, rather than a uniform semantic deficit. In addition, the patient demonstrated difficulty in a non-verbal semantic judgment task (Semantic Odd-One-Out Task), particularly when selecting among semantically close items, indicating impaired resolution of semantic competition. These findings suggest that the impairment was not limited to lexical retrieval processes but may extend to dysfunction in the regulatory (semantic control) mechanisms of the broader semantic processing network. This case provides clinically valuable evidence supporting the role of the thalamus as a key node in the control and integration of distributed semantic networks.