Week 9 - Frontal Lobes

The frontal lobes

The frontal lobes account for approximately one-third of the cerebral cortex and are implicated in a wide range of behaviours including motor control and social behaviour. Additionally, neuroimaging studies have revealed that the frontal lobes have an important role in executive functions (Martin 2006).  

Executive functions

Executive functions can broadly be described as a set of collaborative cognitive tools which facilitate decision making. According to Martin (2006), these  include attention (divided and sustained), processing speed, initiation, sequencing, set-shifting, cognitive flexibility and planning.  Based on Banich (2009), we can elaborate a little on this somewhat definitive list to include inhibition of familiar behaviours, prioritising and the ability to effectively handle novel situations.   Given the complexity of the decision making process, Banich (2009) argues that the potential components of executive function are actually quite extensive, whixh makes testing executive function as a whole somewhat futile. Tests of executive function are therefore best suited to addressing particular components of it.

Some tests of executive function

Tests of executive function include the Wisconsin Card Sorting Test.  Patients are asked to sort cards according to designs based on colour, shape or number.  At random intervals, the experimenter implicitly changes the rule by which the cards are to be sorted.  The patient should ascertain what the new rule is and begin sorting the cards according to this new principle.   Thus, according to Banich (2009) the WCST is testing inference, attentional set creation and set-shifting ability.  Frontal lobe patients and children under the age of four have difficulty in adjusting to the new rule. 


The Stroop Task requires participants to identify the colour of word without saying the word itself.  For example, where the word ‘red’ appears in blue ink, the participant should say ‘blue’ rather than red.  In this case, it is the inhibitory component of executive function that is called upon to ‘override’ the automatic urge to read the word instead of naming the colour.

Demonstration

Finally, the Tower of London Task assesses the ability to plan, strategise and organise (Martin, 2006). Using a set of discs or beads on pegs, participants are required to plan the shortest number of moves from an initial state to the goal state.  Again, frontal lobe patients show impairments on this test, typically beginning the task immediately without any ‘plan’.

Demonstration


Models

In her article, Banich (2009) highlights some differeing models of executive function based on the understanding that there exists several distinct subcomponets of executive function (such as response inhibtion and updating working memory) which are moderated by specific neurobiological regions.  One such theory offered by Petrides (2005, as cited by Baron, 2009) suggests that "inferior lateral regions of the prefrontal cortex ... maintain information in working memory while others, notably mid-dorso-lateral prefrontal regions, perform executive control operations on that information" (p.91).

Banich (2009) suggests that in an effort to further and better explore potential interventions to address executive dysfunction, these competing models might best be integrated to some degree to broaden our understanding of what is a complex and continually evolving field.


References

Banich, M. T. (2009). Executive frunction: the search for an integrated account. Current Directions in Psychological Science, 18, 89-94

Martin, G. N. (2006).  The frontal lobes: cognition, social behaviour and personality. In Human Neuropsychology (2nd ed.). Essex: Pearson Education Ltd