Saturday, September 4, 2010

The New Executive Brain 2: Novelty, subroutines, and hemispheres

1. Yakovlevian torque (see Lemay, Ann Ny Acad Sci 1976) shows the right frontal lobe is wider than and protrudes over the left, and the left occipital lobe is wider than and protrudes over the right.  This present in great apes to some degree, and there are gender differences.  Other assymetries include the planum temporale is larger in left side in human and this is also true in several other primates.  Spindle cells with long axons are more numerous in the right hemisphere.  White matter is more organized in the right than left frontal lobes in children and adults (Klingberg et al., 1999, Neuroreport).  Dopamine is more prevalent in the left hemisphere, norepinephrine on the right, and estrogen receptors are more prevalent on right (rats) Sandu et al, Exp Neurol 1985.  Goldberg argues that hemispheric assymetries exist in animal species and these cannot be based on language since animals lack language.  Is language a "special case" of some larger difference?

2.  Other right - left approaches (analytic/holistic, sequential/simultaneous processing) are difficult to operationalize and are rejected.

3. Bates E argued that in children, left hemisphere brain damage is inconsequential, but in right hemisphere patients it is devastating (in Bronan SH ed, Changing Nervous System:  neurobehavioral consequences of early brain disorders, Oxford University Press, 1999).

4. History of civilisation is right to left shift; translating Vygotsky cultural historical psychology in neuroanatomical terms would reach similar conclusion

5.  In neuropsych tests, averaging across six categories of WCST, the five trials of CVLT, and 30 trials of Benton Lines is not accurate anatomically.  Should rescore old tests with that in mind. 

6.  Agnosias:  leitmotif is left hemisphere is top down process, unable to recognize unique exemplars of generic categories "associative agnosias."  Right hemisphere lesion cannot recognize exemplars as their own selves or as different exemplars of same category ("apperceptive agnosias").  see Goldberg JCEN 1990.

7.  Animals may have paw prefence but its closer to 50-50 unlike humans. 

8.  Frontal function:  divide into perseverative (difficulty with cognitive flexibility) unable to transition from one activity to another; and field dependent behavior (echopraxia/echolalia).  Traditionally these are known as 2 aspects of executive control, ability to guide behavior by internal representations and ability to shift cognitive sets with exigencies.   These may be referred to as "stability" and "plasticity" as well.  Author postulates that D1 receptors maintain low level maintenance of current cognitive regime, and D2 receptors respond only to high levels of dopamine and cause destabilizing rapid updating of the cognitive regime, favoring the right hemisphere.  On Executive Control Battery,  perseveration was twice as common following left hemisphere injury.  Echopraxia was twice as severe after right hemisphere injury.  However, these differences were present only in men.

4. Authors Goldberg and Costa postulated the right hemisphere is important to cognitive novelty and the left to cognitive subroutines (Brain Lang 1981: 144-173).  Information is processed from novel to familiar.  .  The left hemisphere information is stored in better articulated neural networks and easier to access. The right hemisphere is modified at a slower rate than the let hemisphere.  It deals with novelty better due to it contains averaged default representation containing shared  poorly differentiated features of many prior situations.  The evidence that supports include Bever and Chiarello (Science 1974) who showed untrained musicians process with their right hemispheres, trained ones with their left hemispheres.  He discusses obscure / familiar faces as being processed with right and left, (Henson et al, Science 2000).   Alex Martin et al. (Hippocampus, 1997) used PET to show that with presentation of meaningful words, nonsense words, real objects and nonsense objects, the right mesiotemporal lobes were activated with first, novel presentation, decreasing with the second exposure. The left hemisphere activation was constant.  Learning a complex motor skill activated first the right MFG, then late in training left posterior parietal cortex, left dorsal premotor cortex,and right anterior cerebellar cortex (Shadmehr and Holcomb, Science 1997).

More studies:  learning grammar A and B:  initial activation occurred in right ventral striatum, left premotor and anterior cingulum, replaced gradually by activation of right DLF and right posterior parietal (Berns et al.  1997 Science).  Raichle (cereb Cortex 1994) found on  a task of finding appropriate verbs for nouns, in naive condition activated ACC, left prefrontal, left temporal, and right cerebellum, but after practice only left medial occipital was activated.  A task with longer processing has right hemisphere to a greater degree.

5.  Constructs that are analagous to the novelty/familiarity distinction:  Exploration/exploitation ( eg. gambling task, novel learning of task and exploiting task to make money) involved right frontopolar regions and left DLF regions respectively (Daw et al. Nature 2006 and Heekeren et al. Nature 2004).  Another distinction is critic and actor; critic learns to predict future awards and actor uses the rewards to guide behavior.  The "critic"  in an fMRI study is the bilateral putamen and right ventral striatum, and the actor is the left anterior caudate.  This resonates with an older idea that the OF lobes appraise value to person and prefrontal cortex navigates the external world. 

6. Pathologic augmentation of orientating reaction (PTSD) has ep activity mostly in right hemisphere (Metzger, 2005 in Vasterling and Brewin). 

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