Week 9

Executive Functions

Executive functions are generally explained as a set of abilities within the human frontal lobe that help us to guide our behaviour, particularly in unknown situations. These functions include processes like prioritizing and sequencing of behaviour, inhibiting impulsive behaviour, planning, mental flexibility, and decision-making. Due to the wide rage of processes involved, impairments are difficult to be diagnosed through the assesment of a single test. It is therefore suggested to use different tasks to examine different facets.

Most scientists share the assumption of executive functions to effortfully guide goal-directed behaviour. Psychological and neurobiological models however differ highly. Banich, 2011 proposes that different parts of the frontal lobe create a pathway of information to achieve the correct response. Explaining her model however, it can be criticized that alternative explanations have not been taken into account but just briefly overviewed. It is claimed that the posterior part of the dorsolateral prefrontal cortex (DLPFC) first gives notice on the top-down attention, deciding where to focus attention. The mid-DLPFC then decides which of the perceived representations is more relevant for the task. The posterior dorsal anterior cingulate cortex (ACC) determines which response to exhibit and passes the decision on to the dorsal ACC where the final evaluation takes place. If the dorsal ACC accepts the response it will be executed (216 words). If it gets disapproved, a signal gets send back to the Prefrontal cortex to start the process over again.

The intensity of each mechanism increases with the decrease of previous mechanisms in the pathway, and therefore can differ highly in each individual. Moreover the level or activation of certain mechanisms is highly associated with the age of the individual. 

Week 8

Laterality in humans

The human body seems symmetrical in external and internal anatomy, but looking closer, we can observe high levels of asymmetry. Even the brain exhibits a great level of asymmetry, anatomically as well as functionally. Several studies have reported for the left-hemisphere to be rather rational, verbal, linear and analytic, whereas the right-hemisphere seems to be emotional, spatial, holistic and intuitive. Arthur Wigan (1844) was one of the first scientists arguing for our hemispheres to be independent entities. Following, researchers examining split-brain patients supported that statement reporting patients acting as having two separate brains. Further research suggested the left-hemisphere to be mainly involved in language whereas the right-hemisphere showed more activation during visuospatial tasks.

Several single-word studies showed great involvement of the left-hemisphere, however, when expanding to sentences and discourse comprehension, the right hemisphere also seemed to show involvement. Therefore it has been speculated that the right-hemisphere is involved in the sentence's thematic sense. Bottini et al. (1994) found for the right-hemisphere to process metaphors and irony.

A study by De Renzi (1982) argued for the right-hemisphere to be involved in visuospatial abilities. Other scientists however argued for a less defined cut, since the right-hemisphere showed high activity during mental rotation processes, but the left-hemisphere seemed to be involved in other visual tasks. (212 words). Harris et al. (2000) then discovered the right posterior parietal lobe to process extreme rotations, with high levels of decision-making, whereas the left side might rather be involved in simple visual tasks.

In conclusion it can be said, that most cognitive functions are not processed in one hemisphere only. Moreover, their involvement in the task differs in gender and handedness. 

Week 7

The Iowa gambling task and the somatic marker hypothesis

The somatic marker hypothesis (SMH) describes a theory, suggesting that cognitive processes such as decision making can be highly influenced by emotions. One way this hypothesis can be tested has been explained in an article by Bechara et al. (1997) using the Iowa gambling task (IGT). The IGT is a relatively simple decision-making experiment, using rewarding and punishment as consequences for participants decisions. Here, participants have to choose several cards from 4 different decks of card, 2 of which are “good decks” and 2 of which are “bad decks”. Bechara et al. found a significant learning effect, showing that after few trials, healthy participants would choose the good deck rather than the bad one. Additionally, throughout the task, skin conductance response (SCR) was measured, showing a significant increase during more risky decisions.

Patients with lesions in the ventromedial prefrontal cortex (VMPC) failed to monitor such SCRs. Moreover, there was no evidence of a learning effect but a rather deficient way of playing was displayed. These findings supported the SMH, suggesting that patients with VMPC damage have impaired emotional progressing and therefore returned to decks with bad outcomes sooner as normal patients. Their decisions were found to be mainly based on the most recent outcome whereas normal participants managed to learn from their overall experience of all past trials. (200 words). When forming a decision, the brain receives emotional-related marker signals that can be unconscious or conscious, helping to form an adequate decision.

These findings have been supported by Maria and Mc Clelland (2004), who used a replication of the IGT, but did not monitor the SCRs of normal participants or patients. This has been highly criticised by Bechara er al. (2005), since the failure of VMPC damaged patients to display such SCRs stays to be an outstanding mystery. Bechara et al. (2005) argues that rather than not showing SCRs, VMPC damaged patients should rather show an even stronger one, since based on their decision through knowledge and their inner gut feeling seems to form distinct decisions. This would be an interesting area fro further research.