Our minds can range incredibly widely, from shopping to integrated circuits, from sewing to theology. More specifically, our knowledge and memory spans vast scales and topics, as a typical video of micro to macro universe scales shows. How can we handle all this? How and where is it stored, and how it is put together again?
In philosophy this is, part, called the binding problem, which asks how features of perception and conception are put together into the larger concept of, say, a rose. Neuroscience has taken a low-key path of labelling our thought and memory patterns as "schemas", which are sort of cartoons of thought, shaping what new things we can fit into our minds and learn, which may be encoded into memories as engrams. Schemas are the structures which can be added together for larger conceptions, or drilled into and ramified to create new distinctions and greater detail. Operationally, schemas allow someone to learn something quickly instead of slowly, largely circumventing the hippocampus as a way-station for memory consolidation / storage. This is all reviewed in a fine paper from 2012.
A recent paper tried to locate where schema-tized thought gets recombined in the brain, and came up with the angular gyrus, which is a structure in the side of the brain, on the temporal-parietal border, known to function in memory, attention, and cognition. How successful they actually were in showing this is another story. They asked human volunteers to learn a very simple task- a sort of brain teaser pattern recognition task, which could give one of two results, depending on which mode or rule was applied. If one rule set was applied, the shapes seen would give one answer, and if the other was applied, another result. A day later, the subjects where shoved in a fMRI machine and tested for their recall of these rules, looking for where in their brains the activity of applying alternate frameworks or schemas to the problem happened. There were many tasks involved here:
- viewing the screen
- understanding the screen text that specifies which rule to apply (spatial or non-spatial)
- interpreting the colors and locations of the imaged circles
- deciding how to decode the problem
- responding to the task by pressing a button with either index finger
- providing an extra response judging the subject's own confidence, with another screen text and button press
- having one's head in a scanner, with corresponding anxiety, boredom, discomfort, etc.
While these tasks were separated in time, it is still alot to disentangle from the whole-brain scanning which finds subtle differences of brain activity in different regions. Overall, they reported seeing activations in many brain areas. But when taking the difference between runs with different rules only, and on the second day when the subjects presumably had their schemas all set up and were tested on their recall and performance, one region stood out, the angular gyrus.
By way of introduction, they mention:
"The medial prefrontal cortex (MPFC) and hippocampus (HC), together with the parahippocampal cortex (PHC), posterior cingulate cortex (PCC), and angular gyrus (AG) have been identified as regions forming a network that is important for successful (episodic) memory retrieval."
Turning to their own results:
"To sum up, while the MPFC mainly showed increased neocortical coupling during spatial schema retrieval, the PCC was connected to an extensive network of regions during retrieval of both schema conditions. This network consistently involved MTL [medial temporal lobe], MPFC, PCC, and left AG and constitutes a set of brain regions that was previously reported to underlie successful memory retrieval."
At this point they tried to isolate the schema-specific parts of the process, making use of the ambiguous nature of their orginal testing, which had the same shapes/colors mean different things depending on the rules the subjects were taught. Thus their recall, while identical or at least very similar in the visual system, would be different wherever the rules were being applied to retrieve different learned memories. Their question was.. where do the visual processing and the rule application activations converge?
Answer: the angular gyrus. On the first (learning) day as well as the second (recall) day, the visual processing touched here, but the memory processing stream only activated this region on the second day, suggesting that this might be a place that specifically binds prior memories with current perceptions to yield higher-level understanding or cognition.
The angular gyrus is one of the more interesting places in the brain, associated with memory, attention, and out of body experiences. Some suggest, for instance, that it is the site where metaphors are recognized, and where concept integration takes place.
"The fact that the angular gyrus is proportionately much larger in hominids than other primates, and its strategic location at the crossroads of areas specialized for processing touch, hearing and vision, leads Ramachandran to believe that it is critical both to conceptual metaphors and to cross-modal abstractions more generally. However, recent research challenges this theory."
In sum, I view the current work as somewhat sketchy. It is rather difficult to credit their extremely simple experimental protocol with isolating memory schemas specifically, or that the one-day delay created exactly the schema they thought they were looking at by brain scanning. Nevertheless, the field is in a stab-in-the-dark phase, trying to pick apart the incredibly intertwined and dynamic network of the brain, so each attempt, however flawed, is interesting and welcome.
- Incidental citation on the posterior cingular cortex, which is also heavily involved here:
"One of the most striking physiological features of the PCC is its high rate of metabolism. In the human, cerebral blood flow and metabolic rate are ∼40% greater than average within the PCC and adjacent precuneus."
"Therefore, the dorsal PCC is involved in detecting and responding to environmental events that may require a change in behaviour and that are not part of the current cognitive set. We envisage that dynamic interactions between the subdivisions of the PCC and other intrinsic connectivity networks are important for regulating the balance between internal and external attentional focus."
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