More Fuster theory

Fuster’s theory is so interesting that I am posting on it again (see previous post). R. Cabezza gives an good overview of the cognit theory and points to the weaknesses. If you want to look at the original review by Cabezza, (here) is where it can be found, down the list, under “(2004) Networks of the Brain Unite”.

To characterize the cognitive structure of cortical networks, Fuster introduces the term cognit. At the cognitive level, a cognit is an item of knowledge, and at the neural level, an assembly of neurons and their connections. Cognitive functions consist of information transactions within and between cognits. While it is often assumed that networks underlying cognitive functions (e.g., attention network, memory network), involve different brain regions, Fuster proposes that the same cognits are part of different networks, and hence, that “it is the cognits and their networks that have topographical specificity, not the functions that use them”. This idea agrees with a point we and others have made regarding functional neuroimaging data: the same brain regions can be activated by different cognitive functions.

Fuster explains almost every cognitive phenomenon is in terms of cognits, allowing him to cover so much cognitive neuroscience in so little space. “Perception is the activation through the senses of a posterior cortical network, a perceptual cognit…”. Perceptual categories are mediated by high-level cognits that “pool attributes from widely dispersed cognits at lower levels.” Action involves high-level executive cognits feeding into motor cognits. Stored memories are cortical networks just like cognits. “To retrieve a memory is to reactivate the network that represents it”. Priming is the “preactivation of a memory network”. Attentional control involves enhancing the activation of some cognits and suppressing the activation of others. Top-down attention is “feedback from higher cognits upon lower ones” . Working memory is sustained activity of a cognit recently activated for executive function. “Linguistic representations essentially consist of cognits, and linguistic operations such as syntax, comprehension, reading, and writing consist of neural transactions within and between cognits”. Reasoning is the “matching of incoming temporal patterns to those patterns inherent in subnetworks that represent specific long-term facts”. Creativity is the creation of new cognits out of old ones, and consciousness is the activation of a cortical network beyond a certain threshold.

Using a single explanatory device for all cognitive functions yields a cognitive neuroscience model that is both elegant and parsimonious. The downside is that Fuster’s model cannot easily account for cognitive processes with clear cortical modules, such as face processing. … Another concept allowing Fuster to integrate different cognitive neuroscience domains is the perception-action cycle. This cycle is the extension to cortical processes of the basic biological mechanism in which sensory stimuli determine motor reactions that change the environment, leading to new stimuli, and so on. In Fuster’s view, this cybernetic cycle has been expanded in humans to include speech, reasoning, and executive processes, but remains the main causal mechanism of behavior and neural function. The complexity of human cortical function can be dramatically simplified by assuming that there are two main functional regions of the cortex, sensory (occipital, temporal, and parietal lobes) and motor (frontal lobes). Sensory signal and behavioral responses are separated in time, and hence, bridging time is one function of the perception-action cycle, particularly the frontal lobes.

Although most cognitive neuroscientists would agree with the perception-action cycle in principle, few would take it as far when accounting for higher-order cognitive functions. Fuster subdivides cognitive processes into perceptual and executive forms. Perceptual memory is memory acquired through the senses, including semantic memory, whereas executive memory is memory for sequences of behavior. Perceptual attention includes top-down modulation of sensory processing, whereas executive attention corresponds to what are usually called executive control processes. In the language domain, lexical information flows from the posterior perceptual cortex to the frontal executive cortex, where it’s integrated into speech or writing. The development of intelligence in children is also described as progressive expansion of the perception-action cycle. The perception-action cycle provides a wonderful unifying principle, but leads to implications that not every cognitive neuroscientist would accept. … Although some implications of the perception-action cycle may be controversial, the most unorthodox aspect of Fuster’s model is probably his unitarian memory view. Most researchers in cognitive neuroscience of memory assume the existence of multiple memory systems; some assume five systems (working, episodic, semantic, and procedural memory, and priming), some assume three (working, declarative, and nondeclarative memory), but almost everybody assumes at least two systems (working and long-term memory). … Fuster can disregard the explicit/implicit distinction because he does not believe that consciousness determines the neural correlates of memory: “In memory retrieval, the degree of conscious awareness may differ greatly, but conscious awareness per se defines neither the network nor the process of its reactivation”. More generally, Fuster does not seem to believe that consciousness plays a causal role in cognition. As he says in the final page, “consciousness is an epiphenomenona of activity in a shifting neural substrate”.

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