Functional Specialization for Semantic and Phonological Processing in the Left Inferior Prefrontal Cortex

TLDR

Neuroimaging and neuropsychological studies implicate the left inferior prefrontal cortex in both semantic and phonological processing, with evidence of distinct subregions for each function. The study aimed to determine whether distinct regions within the left inferior prefrontal cortex support semantic versus phonological processing. Functional MRI was employed to compare activation patterns during semantic decision and syllable‑counting tasks, contrasting each with perceptual control conditions. Semantic tasks produced widespread LIPC activation, especially in the ventral IFG (BA 47/45), whereas phonological tasks engaged the dorsal IFG (BA 44/45) with stronger activation for nonwords, indicating functionally distinct subregions for semantic and phonological processing.

Abstract

Neuroimaging and neuropsychological studies have implicated left inferior prefrontal cortex (LIPC) in both semantic and phonological processing. In this study, functional magnetic resonance imaging was used to examine whether separate LIPC regions participate in each of these types of processing. Performance of a semantic decision task resulted in extensive LIPC activation compared to a perceptual control task. Phonological processing of words and pseudowords in a syllable-counting task resulted in activation of the dorsal aspect of the left inferior frontal gyrus near the inferior frontal sulcus (BA 44/45) compared to a perceptual control task, with greater activation for nonwords compared to words. In a direct comparison of semantic and phonological tasks, semantic processing preferentially activated the ventral aspect of the left inferior frontal gyrus (BA 47/45). A review of the literature demonstrated a similar distinction between left prefrontal regions involved in semantic processing and phonological/lexical processing. The results suggest that a distinct region in the left inferior frontal cortex is involved in semantic processing, whereas other regions may subserve phonological processes engaged during both semantic and phonological tasks.