Saturday, September 4, 2010

The New Executive Brain by Elkhonon Goldberg I

Goldberg reviews much more information in this book than can be summarized here, but I would like to go over certain information that would be critical to Goldberg's overall "brain view."  I also include random references from the book that are less pertinent but interesting background nonetheless.

Goldberg is a protege of Alexander Luria's, but emigrated from the USSR in the early 1970s, establishing a career in New York, academic, eventually private practice.  He opens with a reference to The Creation of Adam, a painting in the Cistine Chapel that Goldberg presents as representing an allegory of the frontal lobes. 

1.  The left inferior prefrontal cortex becomes active when presented with statements with semantic violations (:"trains are sour").  Hagoort et al., Science 2004.  fMRI study.  Language and executive functions arose together.  Language builds models, executive functions manipulates them and conducts operations on them.

2.  Goal formation is action centered about "I need" not "It is."  Therefore, formation of goals relates to the emergence of the mental representation of the self, in turn related to the development of the frontal lobes.

3.  The dorsomedial thalamus nucelus is the highest point of integration in the thalamus and has many connections with the frontal lobes.  It also maintains connections with the hippocampus (memory), the cingulum (emotion and uncertainty), amygdala (relations among individuals in species) and hypothalamus (in charge of homeostatic functions). 

4.  Goldberg speaks of the "fallacies" of modularity (the high tech revival of 18th century phrenology").  For example, the planum temporale is critical for phonologic processing, but is not narrowly dedicated.  Rather, it is critical for auditory analysis in a categorical sense (is the sound a dog barking, a cat meowing , etc.).  It activates both when phonological discriminations are made and when environmental sounds are matched with their sources.  Fusiform gyrus is associated with facial recognition.  Goldberg differentiates between a prior, preordained modularity and a posteriori, resultant modularity.  A priori means the area is hard wired for the task.  A gradiential view of neocortical organization means that certain tightly  integrated neuronal groupings  emerge over time, due to cognitive history of individual.  This means is has less uniformity, more individual differences and will change over time.  The left hemisphere, which has more dedication to "subroutines" has more modularity and the right hemisphere has less.  Goldberg published his gradiential theory of modularity in 1989 in JCEN and republished as a book chapter in 1990 (Contemporary Neuropsychology and the Legacy of Luria, 1990).  "Modularity is best applied to an evolutionary old structure, the thalamus."  Goldberg discusses the "dynamic topology" of cortex and the evolving role of the thalamus in its new inferior position in the hierarchy, which is a reason its function has been elusive.

5.  Jordan Grafman et al. showed in an fMRI study that when a cognitive task is characterized by a hierarchy of goals, the regions around the frontal lobes are activated when subjects have to keep in mind the main goal while performing subordinate goals (Nature, 1999).  This was supported by D'espositio et al.who showed that increasingly abstract goals activate increasingly anterior portions of the frontal lobes.  Anterior prefrontal cortex  has a high number of dendritic spines per cell and high spine density, making it ideal for a variety of inputs.

6.  E Koechlin et al (Science 2003) introduced the notion of a "hierarchical cascade of executive processes."   The control operates in Brodman areas 6 (premotor), 44/45 (inferior frontal) and 46 (middle prefrontal) at level of stimuli, perceptual context, and temporal episode, respectively.  Goldberg analogizes to perseveration  of elements , features and activities, respectively. 

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