Do Semantic Categories Activate Distinct Cortical Regions? Evidence for a Distributed Neural Semantic System

Abstract

A key issue in cognitive neuroscience concerns the neural representation of conceptual knowledge. Currently, debate focuses around the issue of whether there are neural regions specialised for the processing of specific semantic attributes or categories, or whether concepts are represented in an undifferentiated neural system. Neuropsychological studies of patients with selective semantic deficits and previous neuroimaging studies do not unequivocally support either account. We carried out a PET study to determine whether there is any regional specialisation for the processing of concepts from different semantic categories using picture stimuli and a semantic categorisation task. We found robust activation of a large semantic network extending from left inferior frontal cortex into the inferior temporal lobe and including occipital cortex and the fusiform gyrus. The only category effect that we found was additional activation for animals in the right occipital cortex, which we interpret as being due to the extra visual processing demands required in order to differentiate one animal from another. We also carried out analyses in specific cortical regions that have been claimed to be preferentially activated for various categories, but found no evidence of any differential activation as a function of category. We interpret these data within the framework of cognitive accounts in which conceptual knowledge is represented within a nondifferentiated distributed system.

Subliminal Convergence of Kanji and Kana Words: Further Evidence for Functional Parcellation of the Posterior Temporal Cortex in Visual Word Perception

“…In fact, this part of the left middle temporal gyrus has been associated with the semantic network by both functional brain imaging (Chao, Haxby, & Martin, 1999;Buchel, Price, & Friston, 1998;Vandenberghe, Price, Wise, Josephs, & Frackowiak, 1996) and neuropsychological studies (Chertkow, Bub, Deaudon, & Whitehead, 1997). More recent work further suggested that the same region is invariably active during semantic judgment of objects irrespective of their categories (Tyler et al, 2003). Using fMRI, Thompson-Schill, D'Esposito, and Kan. (1999) also observed activation reduction of the left inferolateral temporal cortex associated with the repeated retrieval of semantic knowledge.…”

The Evolution of Meaning: Spatio-temporal Dynamics of Visual Object Recognition

“…Posterior regions of the ventral temporal lobe are routinely found to be active during visual object processing (Haxby et al, 2001;Grill-Spector et al, 1998;Malach et al, 1995), and these same regions are implicated in processing the semantic information about objects (Bright, Moss, & Tyler, 2004;Tyler et al, 2003;Chao et al, 1999). The neurons in these regions have been found to respond to moderately complex information about an object (Tanaka, 1996;Kobatake & Tanaka, 1994), whereas whole objects are represented through distributed patches of neural activation (Tsunoda, Yamane, Nishizaki, & Tanifuji, 2001).…”

“…The neural infrastructure that supports this key cognitive function has been extensively investigated in nonhuman primates, resulting in a well-developed model of hierarchically organized object processing in ventral occipito-temporal cortex (Felleman & Van Essen, 1991;Ungerleider & Mishkin, 1982) that also supports the semantic processing of visual objects (Moss, Rodd, Stamatakis, Bright, & Tyler, 2005;Tyler et al, 2003Tyler et al, , 2004Chao, Haxby, & Martin, 1999). Although this research has been key in identifying the neural architecture that supports the recognition of visual inputs as meaningful objects, a comprehensive model of the neural mechanisms involved in processing meaningful objects requires the characterization of dynamic interactions along the ventral stream.…”

Task-specific change of unconscious neural priming in the cerebral language network

“…Neuropsychological (21,22) and functional brain imaging (23,24) studies converge to suggest that this region is associated with amodal, conceptual-level representations. Our finding thus suggests the existence of another distinct component of cross-script priming that is mediated by the activation of semantic knowledge.…”