User:Graeme E. Smith/Symbolic Memory: The Striate Cortex and its Roles

The Striate Cortex and its Roles Graeme E. Smith, GreySmith Institute of Advanced Studies  http://en.wikiversity.org/wiki/Portal:GreySmith Institute   http://en.wikiversity.org/wiki/User:GreySmith Institute  grysmith@telus.net Nestled in below the cerebral cortex and above most sub-cortical organs, is a flap of cortex that stains as a stripe when a serotonin stain is used. Called the Striate Cortex because of its stripe, This cortex is intimately involved with the sub-cortical functions. In this article I explore a plausible set of roles for the striate cortex and its sub-elements.

The cerebral cortex, consists of a hankie sized structure that folds over on itself, and wraps around the top of the brain. The area of the cortex that lies underneath the fold, is slightly differently organized than the areas on top of the fold, as is evidenced by the fact that it stains a solid stripe when stained with a serotonin finding stain. It is important to realize that all sub-cortical functions that are connected to the cerebral cortex, must pass their connections through this layer. Although the connections can penetrate through the layer without connections within the layer, and many do, other connections from both the cerebral cortex, and the sub-cortical functions terminate in this layer, creating a sort of interface that is informed from both the Cortex, and the sub-cortical organs. This makes this area of the brain an ideal platform for bringing together certain types of functions that need to fuse sub-cortical support services with cortical information. A good example is the Limbic System. It has long been wondered how the limbic system affects thought. The limbic system lies in the sub-cortical support circuitry, and thought, it is thought, seems primarily to happen in the frontal areas of the brain. There is a question of how the sub-cortical services can so strongly affect the frontal areas, and the answer might be at least partially in the striate cortex. To understand this let us look at the thalamic function. The thalamus is a sub-cortical organ, that is tightly associated with the Reticular Activation System. In The Dual Mode Cortex I discussed the role of Dr. LaBerges theories about the attention system in creating a demand memory that ported onto the natural phenomenally implicit memory, in Phenomenally Explicit Memory: Scope and Limitations I discuss the nature of the explicit memory system that this creates. Because the nature of the memory I describe in Phenomenally Implicit Memory: Scope and limitations is such that it can't separate out distinct memories from the phenomenal data-field, it makes sense that any thought, having to deal with those distinct memories must be by definition happening after the conversion from implicit to explicit memory. This definition means that thought is dependent on a sub-cortical process, which must, by its location in the brain pass its signals through the striate cortex. However the information that is passing through the straite cortex, is the addressing information associated with phenomenally explicit memory. At first this might seem counter productive, if the content of the memory is in the cortex, why would we want to process address data? This is an important question, because it stresses the limitations of Phenomenal Memory. The nature of phenomenal memory is that the Quale it creates cannot be subdivided, so the only way to manage the quale is to subdivide the addressing CLUMP. We can say that the addressing data in the clump implies the quale. If so, then indeed we should be processing the addressing data instead of the Qualar data-field, because the addressing data is more unique to the data than the qualar output is. On another level, we need to be able to link addressing information to the Qualar contents it represents. Here we get into an interface problem, how do we interface the Qualar contents to the address information so that we can process the address information and imply the qualar contents? One answer is that within the perception process, specialized processing modules, link their output to the limbic system. Because it is a direct connection from one neural network to another, it is not as qualar in nature, although the output is still phenomenal within the connection. Thus modules can activate specific limbic organs whenever the quale includes data that triggers that module. In other words our Carnivore Detection modules can trigger the fear reaction when we get too close to a tiger. The trick then becomes how to associated the fear reaction with the address of the tiger memory element so that we know that the tiger is what we fear. It is my suggestion that in fact the Striate Cortex is likely to have just such a role. It associates Limbic reactions with Thalamic Address information so that we explicitly know that tigers are scary. This is interesting because it means that implicit registration of the stimuli, is all that is needed in order to trigger explicit connections between elements that are known and the emotions that we know them by. In other words the question of salience becomes less of a mystery, because we know how limbic reactions can be associated with specific elements. If salience is dependent on the association of limbic reactions to explicit addresses, then the ability of the Basal Ganglia to react and Orient the body, towards salient zones of the environment must mean that it is taking into account this type of information even before the explicit memories are activated. this implies a strong connection between the striate cortex and the basal ganglia. In fact some theorists have suggested that just such a connection exists via the Nucleus Accumbens. But the Nucleus Accumbens has also been implicated as the link between the PFC and the Thalamus, in the sub-clump addressing mechanism needed to isolate specific memories. this suggests a more general role, possibly linking symbolic links in other memory systems, to Thalamic output arrays needed to select a particular memory in the Cerebral Cortex and to trigger Basal Ganglia instinctive reactions. An example of this might be the orienting of the body towards a location that in the past has hidden a danger despite the fact that it is not yet in sight. The location of the danger is held in episodal memory, but the body orients towards it anyway. This classic response, is the meat of slasher flics where the actor is oriented towards one danger and backs into another or the same danger mysteriously transported to behind them. It is always a good hook for a thrill. It is also a good hook for comic relief, when the actor backs into something mysterious that turns out to be innocuous after all. Usually its good for a chuckle of relief. We wouldn't have these reactions if the actors body language didn't indicate that they were oriented on a danger, and vulnerable to dangers outside their orientation.((indent|8}}This tendency to orient our bodies towards danger may be good for gags in movies, but it also indicates a connection between the Declarative Memory and the Basal Ganglia that more or less has to be re-routed through the striate cortex. The Declarative Memory however is in the sub-cortical areas, as is the basal ganglia, so we can see that the striate cortex might also act as a communications center for sub-cortical functions. All this communication and processing cannot be done, unless somehow the address is standing symbolically for the content of the cerebral cortex it addresses. However evidence of size invariant coding in the Declarative Memory, specifically in Episodal memory suggests that the addresses are further symbolized by single neurons in the map. this suggests a mapping function that can address a single neuron, and associate it with a CLUMP address array. If so this also might be a function of the striate cortex.