How our brains combine simple concepts into more complex ideas

or, technically, 
Converging evidence for the neuroanatomic basis of combinatorial semantics in the angular gyrus. [See the original abstract on PubMed]

Authors: Amy R. Price, Michael F. Bonner, Jonathan E. Peelle, Murray Grossman

Brief prepared by: Meghan Healey
Brief approved by: Shivon Robinson
Section Chief: Isaac Perron
Date posted: May 3, 2016 

Brief in Brief (TL;DR)

What do we know: Humans are able to represent individual concepts and combine them into more complex concepts. For example, we can take the concepts “wet” and “leaf” and combine them to form another meaningful concept: “wet leaf.” While this seems intuitive to most people, some patients with dementia have difficulty combining concepts into meaningful ideas. 

What don’t we know: Scientists do not know how the brain does this and which regions are involved. 

What this study shows: The researchers found a specialized brain region, termed the angular gyrus, that supports the process of conceptual combination. This is true in both healthy adults and patients with neurodegenerative diseases. 

What we can do in the future because of this study: Future studies can examine other factors, like grammatical category (e.g. nouns vs adjectives) or type of input (e.g. words vs pictures), that may affect an individual’s ability to combine concepts. 

Why you should care: By learning more about the brain basis of conceptual combination, we may be able to develop new ways to improve language comprehension in patients with dementia.

Brief for Non-Neuroscientists

Humans can build an unlimited number of concepts by combining individual concepts into more complex representations. For example, the concepts “plaid” and “jacket” can be represented independently, or integrated into a more complex and more meaningful representation: “plaid jacket”. While previous studies have examined the cognitive processes that may be involved in this type of conceptual combination, very few studies have examined what parts of the brain support this fundamental process. In this study, researchers used both classic and functional magnetic resonance imaging (MRI) to observe brain structure and activity, respectively, to determine which brain regions are necessary to complete a conceptual combination task. The results showed that a specific brain region—the angular gyrus—is active during a conceptual combination task and its atrophy is correlated with decreased ability to perform this task. This finding adds a new role for the angular gyrus, which was already known to connect language regions, sensory regions, and motor regions of the brain. This allows us to better understand the brain circuitry that supports advanced linguistics and semantics, which may allow the development of better therapies to treat patients with dementia or other disorders affecting word comprehension.

Brief for Neuroscientists

Combinatorial semantics refers to the ability to construct complex concepts from individual constituents. For example, the basic concepts “plaid” and “jacket” can be integrated into a more sophisticated representation: “plaid jacket.” While theories of semantic memory have addressed how and where individual concepts may be represented in the brain, surprisingly little is known about the neuroanatomic basis of more complex representations. Here, researchers investigated the hypothesis that conceptual combination is dependent not only on primary sensory and motor cortices, as is the case with individual concepts, but also high-level association cortices. Using two complementary neuroimaging techniques (functional neuroimaging in healthy adults and structural neuroimaging in patients with focal neurodegenerative disease), Price et al. found that the angular gyrus, which has extensive connections to sensorimotor and language regions throughout the brain, plays a critical role in conceptual combination. Delineating the neural substrates supporting combinatorial semantics may have future implications for the treatment of individuals with semantic dementia.