Semantic cognition is the collection of processes that allows us to use our stored knowledge to understand concepts, objects, and language. This is different from semantic memory, which is simply possessing information; semantic cognition is about the active and flexible use of that knowledge. If our knowledge is a mental library, semantic cognition acts as the librarian, skillfully finding the precise information needed for a given situation.
This cognitive ability underpins language, object recognition, and our capacity to generate appropriate actions. When we encounter a familiar object, semantic cognition allows us to access information beyond its name, including its function, how to interact with it, and in what contexts it is found. This process is dynamic, allowing us to adapt our understanding and behavior as the context changes.
The Core Processes of Semantic Cognition
Semantic cognition operates through two primary components: semantic representation and semantic control. Semantic representation refers to how our conceptual knowledge is stored and organized in the brain. The “hub-and-spoke” model explains this organization, positing that a central “hub” integrates information from various sensory and motor areas, known as “spokes.”
For instance, our knowledge of a “lemon” is not a single fact but a collection of attributes distributed across different brain regions. The visual cortex stores its yellow color and oval shape, the somatosensory cortex holds the texture of its rind, and the gustatory cortex contains its sour taste. The ATL hub binds these disparate sensory “spokes” into a unified, coherent concept of a lemon.
While representation provides the library of knowledge, semantic control selects the appropriate information for a specific context. We possess vast information about any concept, and not all of it is relevant at all times. For example, when considering a “piano,” its musical qualities are foremost if we intend to play it, but its physical attributes like weight and size become the focus if we need to move it. Semantic control mechanisms suppress irrelevant associations and retrieve information that aligns with our goals. This ensures our thoughts and actions are context-appropriate.
Brain Networks Supporting Semantic Cognition
The processes of semantic cognition are supported by a distributed network of brain regions with specialized functions. Our understanding of this network comes from neuroimaging techniques like fMRI and from studying individuals with brain damage. These methods help delineate the areas responsible for storing and controlling semantic knowledge.
The “hub” of semantic representation is located in the anterior temporal lobes (ATLs). Evidence indicates that both the left and right ATLs work together to form these conceptual representations. Damage to these areas results in a loss of concept knowledge itself, while the “spokes” are distributed across modality-specific cortices like the visual and motor cortex.
Semantic control is managed by a different set of brain regions, predominantly in the left hemisphere. This network includes the inferior frontal gyrus (IFG) and the posterior temporal cortex (pMTG). The IFG is thought to play a role in selecting the appropriate information from competing alternatives. The posterior temporal regions help to constrain and refine the activated concepts based on the current context.
Semantic Cognition in Everyday Life
Semantic cognition is fundamental to our daily experiences, especially language. It enables us to go beyond the literal meaning of words. When we understand a metaphor, such as “the lawyer was a shark,” we use semantic cognition to suppress literal animal features and focus on abstract qualities like aggressiveness and tenacity.
This process also allows us to use objects and tools effectively. Upon seeing a screwdriver, we instantly know its function and how to use it without explicit instructions. This involves accessing our stored knowledge about the object’s purpose and the actions associated with it, bridging our knowledge with practical action.
Semantic cognition is also active in social interactions, where we infer others’ intentions based on our knowledge of social norms. It also supports our ability to categorize new experiences. For instance, if we encounter an unfamiliar fruit, we use our existing knowledge of “fruit” to infer that it is likely edible and might be sweet.
When Semantic Cognition is Impaired
When the brain networks supporting semantic cognition are damaged, a person’s ability to interact with the world is affected. The symptoms depend on which component is damaged: the knowledge store itself or the mechanisms that control its access. This distinction is illustrated by comparing semantic dementia with semantic aphasia.
Semantic dementia is a neurodegenerative disorder characterized by the progressive loss of concept knowledge from atrophy in the anterior temporal lobes (the semantic “hub”). Patients gradually lose the meaning of words and objects. They may struggle to name a familiar object, not because they cannot find the word, but because the underlying concept has degraded. For example, they might lose the knowledge that a sheep has wool or what a kettle is used for. This loss is consistent across all modalities, affecting understanding, recognition, and object use.
In contrast, semantic aphasia is an impairment of semantic control rather than a loss of knowledge, often resulting from a stroke. The damage involves regions like the left inferior frontal gyrus or posterior temporal cortex. A patient with this condition might know what a “pear” is but say “apple” when asked to name one, as they cannot select the correct word from related concepts. Their knowledge is present but difficult to access in a context-appropriate manner. Providing a cue can often help them retrieve the correct name, highlighting that the representation is intact.