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Cortical Representation of Abstract Semantic Knowledge

Periodic Reporting for period 3 - CRASK (Cortical Representation of Abstract Semantic Knowledge)

Reporting period: 2018-05-01 to 2019-10-31

Conceptual representation in the brain has been studied in terms of simple concepts, like an apple (a red/green, round, edible, fruit). The challenge of CRASK is to move beyond this to our complex encyclopaedic knowledge (the rebellious Swiss, William Tell, once shot an apple off his son's head with a crossbow). CRASK uses magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) to meet this challenge. First creating a cortical systems-level model of simple concepts, then using this to unlock how the brain creates the combinatorial world-knowledge that is so important for our daily lives.

World-knowledge plays a big role in our professional, scholastic and interpersonal success. CRASK is motivated by the belief that understanding how this knowledge is instantiated in the brain will allow us to better understand what makes some individual better at knowing things than others, why our ability to access our stored knowledge is sometimes transiently blocked and how our ability to access knowledge changes over the lifespan.
In the first half of this project, we have exploited the brain’s propensity towards interactions with conspecifics to characterise how complex knowledge is stored in the brain. In particular, when we are presented with a familiar person, the regions of the brain's 'semantic system' are spontaneously recruited. Taking advantage of this, we used fMRI in a novel way, overloading the system through the rapid presentation of stimuli (famous faces) to determine how long different brain regions are activated (regional 'time constants'). Knowing how long a brain regions takes to perform its cognitive function gives us insight into the depth and complexity of the type of knowledge stored in this region. The results are surprising an interesting. While regions involved in perceiving the faces of other people show a defined hierarchy - with progressively longer time constants in brain regions associated with more sophisticated stages of face perception - regions involved in knowing about others people tend to stay active for the same amount of time (about .8 seconds when looking at a famous person). This suggests that these distributed brain regions share information and coordinate with each other to endow us the rich and diverse information we have about other humans. In a separate study, we looked at how the coordination between these same brain regions changes when we access a famous person's name, facts about them, social information, personal memories or physical characteristics. This allowed us to determine that the brain processes and stores factual information and personal memories in a similar way as well as understanding the role that each part of the brain network contributes to the overall picture.
In another line of research where we considered whether the mode by which we form knowledge about a category shapes the representation of facts. Specifically, we asked our Italian subjects to retrieve the part of Italy traditional Italian food dishes come from. We observed that a specific part of the brain, the insula, was active when encyclopaedic information was retrieved about food (but not about people or cities). This is interesting as the insula is involved with taste information but our research seems to suggest that this brain region is co-opted by abstract information that has little to do with taste, as long as it relates to the category 'food'.
These are examples of a line of research that intends to uncover the principles by which our factual knowledge of the world is encoded in the brain.
Now CRASK has moved on to investigate general semantic knowledge in terms of the relative contribution of canonical, feature-selective and category-selective semantic representations and their respective roles in automatic and effortful semantic access. The systems level model of semantic representation will be used to predict and test how the brain manifests elaborated semantic knowledge. The resulting understanding of the neural substrates of elaborated semantic knowledge will open up new areas of research. In the final stage of CRASK we chart this territory in terms of human factors: understanding the role of the representational semantic system intransient failures in access, neural factors that lead to optimal encoding and retrieval and the effects of ageing on the system.