Effects of brain damage, especially that to the frontal lobes Essay
The frontal lobes are considered out emotional control centre and home to out personality. There is no other part of the brain where lesions can cause such a wide variety of symptoms (Kolb & Wishaw 1990). The frontal lobes are involved in motor function, problem solving, spontaneity, memory, language, initiation, judgement, impulse control and social and sexual behaviour. They are extremely injury prone as due to their location at the front of he cranium and their large size shown by MRI studies (Levin et al 1987). In this essay I will be discussing impairments caused by the frontal lobes, discussing the executive function of the frontal lobes and putting forward an explanation as to why the defects occur in relation to thinking and remembering.
The case of Phineas Gage, a railroad foreman who had a horrific accident where a 1-foot iron rod got lodged through his skull has shown significant side effects of frontal lobes damage to social behaviour. Those close to Gage described him as hardworking with good prospects ahead of him, however after the accident he was described as unreliable, nasty, vulgar, disrespectful with an inability to plan. They said ‘he was no longer Gage’. Phineas Gage, like many other frontal lobe patients had problems with his memory, where he reported falsely, this deficit is termed confabulation. Those with frontal lobe damage can make momentary confabulations, which could be correct in the patients circumstances however aren’t or in extreme cases fantastic confabulations which are recollections which are clearly fictional in the view of everyone else but the patient.
Frontal lobe damage has shown to affect remembering and thinking and studies on memory impairment have highlighted this. The impairments I will be discussing are source amnesia, temporal order, metamemory, false recognition and defective recall.
Schacter (1984) showed how frontal lobe damage is related to source amnesia. In his experiment colleagues spoke fictitious sentences and frontal lobe patients were asked to recall what they said and if they could recall what they said they had to identify the source of the sentence (i.e. which experimenter spoke it). Patients had normal memory for facts (semantic) however they made source errors shoeing a lack of remembering within episodic memory. Janowsky (1989) also supported the link of frontal lobe dysfunction and amnesia showing poor episodic memory retrieval.
Corsi (1991) found affects of frontal lobe damage and remembering for temporal order tasks. He presented subjects with pairs in the study task. In the test situation pairs were shown again, however in different combinations where subjects had to recall for old stimuli. If the pair included a new and old stimuli it involved recognition, however if it involved 2 old stimuli it tested recency between each stimuli. The study found that those with frontal lobe damage showed impaired ability for recency discrimination therefore showing problems in remembering temporal order, however were normal for recognition. Shimamura (1990) found similar results for temporal order difficulties where frontal lobe subjects were unable to put a recalled list in sequence order.
Metamemory refers to the ‘feeling of knowing’ something even if you cannot remember it. Janowsky (1989) tested metamemory of frontal lobe patients for a number of sentences where they had to recall the key word. If they were unable to they were asked to rate their ability of recognising the key word i.e. metamemory. They found that those with frontal lobe damage had impaired metamemory relative to the control group. Showing the effects of damage to remembering the ‘feeling of knowing’.
False recognition tasks comprise of a random sequence of items with previously seen items called targets and novel items called distracters. For forced choice tests where stimuli is shown with alternatives, if a patient is correct in identifying the target it is called a hit, if they are unable to answer it is called a miss and if they answer incorrectly it is called a false alarm. This method is used to test memory and remembering ability of previous targets. Delbecq – Derouse (1990) studied patient RW and found that he made large numbers of false alarms on a forced choice test. Investigators report was that RW’s manner indicated that he was as sure about these false alarms as much as he was about hits. This shows his confidence remains similar in both cases of hits and false alarms revealing inability to remember and think through, leading to intrusions guiding judgement.
The frontal lobes are known to play an important role in the planning and the executive of response strategies (Karnath et al., 1991). This aspect of frontal lobes as ‘executive’, has been described by Norman and Shallice (1986). They suggest that ongoing activity comprises of routine automatic responses that require no conscious intervention, for example when driving where actions are performed without thought. However when proposed with a novel situation a plan needs to be formulated in response, and control passes to the Supervisory Activating System (SAS), for example when driving abroad.
Shallice (1988) has concluded that those with frontal lobe damage have impairments to their SAS therefore find difficulty in either formulating the description of memories or in deciding whether retrieved memories are appropriate. This finding was evident for Hanley et al (1994) case study on ROB a woman with damage to her left caudate nucleus, a structure closely related to that of the frontal lobes. She had problems with formulating descriptions at retrieval causing affects on recall and not on recognition, as ‘to be retrieved’ information in not necessary as only a decision on appropriateness is needed.
Norman and Shacter have provided an alternative explanation as to how frontal lobe damage affects memory. They argue that it is due to a poorly focused retrieval system with weak criterion for evaluating retrieved memories. This theory accounts for why frontal lobe patients have poor false recognition as they have a weak criterion for accepting an item as a target with a attitude of ‘I saw a bunch of words’ thus not paying attention to the detail. Also false alarms may occur due to familiarity, as patients maybe using availability heuristic.
Whether to support Shallice’s theory or Normal and Schacter it is important to observe that both theories locate the role of the frontal lobe function at retrieval. Thus both theories argue that frontal lobe damage in some way impairs access to memory by producing vague descriptions of what is being sought. However the problem of this theory assumes the event description arises independently of the memory that is being sought, therefore it could be defects in encoding as opposed to retrieval. In order to produce a description of an event information is needed therefore the description depends on the quality of representation of the target event. Possibility of encoding factors could influence quality of an event description. Frontal structures decide which aspects should be encoded and influences ease at which an event description evolves. Shallice (1994) however distinguished between encoding and retrieval operations and examined the pattern of brain activity resulting from each, where they right frontal lobe was associated with encoding operations and the left frontal lobe was associated with retrieval operations.
While the exact nature of the impairment remains to be explained it seems reasonable to conclude that research has shown clear evidence that frontal lobe damage has various different effects on an individuals thinking and remembering. This maybe due to faulty retrieval in the cases of both recognition and recall, it could be due to defective encoding or both, shown in source amnesia and temporal order deficits. Confabulations however remain inconclusive as to where the defect lies. Overall all the impairments have shown us that the frontal lobes serve as an executive system which guide retrieval and confirm the status of retrieved memories.