Some research has supported the view that with continued nicotine dependence the brain functions is disrupted having an effect on the cognitive performance. The effects of nicotine and smoking on human cognitive performance have been found to be varied as with some research showing deficits, some improvements and others showing no effects at all.
Spilich, June and Renner (1992) focused on the working memory with respect to the capacity of information one can process and observed what effect smoking might have upon cognition.
Spilich et al accessed regular smokers and non-smokers. The regular smokers were divided into two groups; a group who had just smoked, and a second group who had been deprived for 3 hours prior to the study. All three groups (non-deprived smokers, deprived smokers, and non-smokers) were compared on a series of tasks. The participants first completed a visual search task (where they had to identify a target letter in a visual array); a visual-attentional task (where the participant had to record text changes in letters on a computer screen); a Sternberg memory test (where the person had to identify a previously presented item on a computer screen); a comprehension task (where an ambiguous array of data appeared on the screen and the participant had to de-code, rearrange and make sense of the confusing data); and the fifth task was a driving simulation test that comprised a road race task which required multi-tasking. The findings revealed that while cigarette smoking had positive effects on the performance of simple tasks, it had negative effects upon the performance of tasks that required problem-solving skills, such as the road race task, which rely on working memory and long-term memory systems. They concluded that tasks in which more complex cognitive skills are involved smokers performed worse than non-smokers (Spilich, June and Renner, 1992).
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Heishman and Henningfield (2000) studied the effect of nicotine administration to non-smokers across an 8 day period. Twelve non-smokers were administered four doses of nicotine gum each day in the order 0mg, 2mg, 4mg and 8 mg of nicotine and their performance on a number of tasks were measured. Working memory was measured by instructing the participant to search for a series of letters within an array and measuring accuracy in recall and speed. A second working memory task included a digit recall task in which the participant had to identify the missing digit from a previously presented series of digits. The findings revealed that nicotine increased the rate of responding on the working memory tasks but accuracy in recall declined. This study supported that nicotine produces deficits in complex cognitive tasks (Heishman and Henningfield, 2000).
Ernst et al (2001) tested 14 current smokers, 15 previous smokers and 9 people who had never smoked on cognitive performance. The tasks comprised of a visual attention task (a search for 2 letters in an array of letters), a verbal reasoning task, and an N-back working memory task (where a series of items are presented individually and the person has to identify whether a particular item appeared on the 1st trial before, 2 trials before, and so on). A double-blind procedure was utilized using gum that either contained nicotine (4 mg) or a placebo. The smokers were asked to refrain from smoking for 12 hours prior to the tests which began each day at 8 a.m. The results indicated that there were no interactions of nicotine ingestion (or placebo) with group type (smokers, previous smokers, never smoked) on any of the tests. It was noticed that nicotine gum increased reaction time when compared with the placebo, but did not produce any enhancement with verbal reasoning and produced actual declines in accuracy in working memory (Ernst et al, 2001). Therefore, it was concluded that nicotine ingestion leads to decline in complex cognitive tasks in relation to working memory.
Other studies have examined cigarette smoking in comparison to cognitive performance in middle-aged subjects Kalmijn, Botel, Verschuren, Jolles and Launer, (2002) used a battery of neuropsychological tests that measured memory function (a letter digit substitution test) and a word fluency test (where one names as many animals as possible in 60 seconds), a Stroop Colour Word Test, and cognitive flexibility (time taken for higher order information-processing) on men and women aged 45-70 years. Current smokers scored significantly lesser than non-smokers and previous smokers on the verbal learning test and the Stroop test. The previous smoker’s scores ranged in between those of smokers and non-smokers. Current smokers were found to have reduced psychomotor speed and reduced cognitive flexibility (Kalmijn, Botel, Verschuren, Jolles and Launer, 2002). Therefore, it was concluded that the effects of smoking impaired cognition leading to cognitive deficits.
Hill, Nilsson, Nyberg and Backman, (2003) studied the relationship between cigarette smoking and cognitive function in healthy Swedish adults (aged 35 – 80 years), comparing current smokers with people who had never smoked. They tested the two groups on a Block design task that involved learning 12 unrelated nouns while simultaneously sorting a deck of playing cards into two piles. Then the participants were tested on two untimed tasks, one task tested general knowledge about Swedish people and the other was a word comprehension task. Smokers showed poor performance on more demanding cognitive tasks (i.e. the Block design task which involved multitasking). As well as, the number of cigarettes smoked and time spent smoking was associated with poorer performance on the Block design task. The between-group differences were noted not noticed on the other two untimed tasks. They concluded that cigarette smoking will have a harmful effect on cognitive tasks that require higher mental processing (Hill, Nilsson, Nyberg and Backman, 2003).
Richards, Jarvis, Thompson and Wadsworth, (2003) studied the effects of cigarette smoking in the middle age-group on a range of tasks. Using a sample of over 1900 people aged 35, 43 and 53 years of age with a smoking frequency of 0, 1 to 20, 20 or more cigarettes per day. The participants were measured on verbal memory (the free recall of words across a series of trials). Speed and concentration was measured by a visual search test where participants were asked to delete target letters within an array of letters within 1 minute. The results of the study indicated that cigarette smoking was associated with a faster decline in verbal memory and slower visual search speed with respect to the different age groups. The self-proclaimed smokers between the ages of 43-53 years mentioned that smoked above 20 cigarettes per day showed the greatest decline when compared to non-smokers. It was concluded that smoking in mid-life was directly associated with increased cognitive deterioration whereas those who smoke into later life may be at very high risk of clinically significant cognitive decline (Richards, Jarvis, Thompson and Wadsworth, 2003).
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One study that used a variety of memory tests in order to determine the effects of chronic smoking on the cognitive performance of adolescents was Jacobson, Mencl, Constable, Westerveld and Pugh, (2005). They assessed the performance of adolescent smokers, abstinent smokers and non-smokers on verbal memory tests (Hopkins Verbal Learning Test – Revised) that involved the immediate and delayed recall of verbally-presented words. Working memory was also tested using the N-back procedure which measured monitoring and recall within working memory. The results revealed that smokers showed no impairments on the verbal learning task but had significant impairments on the working memory performance tests (the N-back task), when compared with the non-smokers. Smoking abstinence produced even more severe deficits on the working memory tasks (Jacobson et.al, 2007). It was concluded that a history of smoking has a harmful effect upon working memory performance (but not on a simple verbal memory recall task) and when smokers were kept in abstinence they showed even poorer performance based on complex working memory (Jacobson, Mencl, Constable, Westerveld and Pugh, 2005; Jacobson et.al, 2007).
Fried, Watkinson and Gray, (2006) conducted a longitudinal study to study the effects of current and past regular cigarette smoking in 112 young adults. They were evaluated using a battery of neuro-cognitive tests administered to the participants at 9-12 years of age, before they started smoking regularly and then again at 17-21 years. The smokers provided self-reports of their smoking habits as being heavy (more than 9 cigarettes per day) and light (less than 9 per day) for current smokers and former smokers (those who had not smoked within the last 6 months). They also included a control group who had never smoked. Each of the groups completed a series of cognitive tasks, including IQ tests, memory tests (the immediate and delayed recall of items), processing speed (the speed at which one can recall items), sustained attention, vocabulary and abstract reasoning tests. The results of the tests indicated that current regular smokers performed worse than non-smokers on the verbal/auditory tasks, oral arithmetic and auditory memory. Former smokers differed from the non-smokers only in the arithmetic task indicating some improvement (Fried et.al, 2006).They concluded that regular smoking during early adulthood is associated with cognitive impairment but that these defects may be reversed when smoking is stopped
More recent research has also found that smoking is associated with a greater risk of poorer memory in middle age populations (Sabia, Marmot, Dufouil and Singh-Manoux, 2008). They used the Whitehall II study of people aged between 35-55 years (measuring general health behaviour and status) as a baseline Of the original number of 5346 participants only 4630 were able to be retested five years later by Sabia et al. They tested these on a memory reasoning task (where the participant had to verify whether a statement was correct/ incorrect) and verbal fluency (described earlier in the thesis). After adjusting for age and sex, smokers performed worse on memory recall and fluency tasks when compared with non-smokers and ex-smokers. Sabia et al concluded that continued smoking was associated with a greater risk of poorer memory (Sabia, Marmot, Dufouil and Singh-Manoux, 2008).
Mendrek, Monterosso, Simon, Jarvik, Brody et al, (2006) designed a study to examine effects of cigarette smoking and withdrawal on working memory. They compared 15 smokers and 22 non-smokers on the N-back task that was administered in two test blocks on each of two days. On day one, smokers were tested after more than 13 hours of abstinence and on another day testing began less than an hour after smoking. Results of the study showed that the performance of smokers after the 13 hour deprivation was significantly less accurate than that of the non-smokers, whereas at the 1 hour abstinence period there was no difference between their performance and that of non-smokers. They concluded that their findings provided further evidence for a deficit in working memory associated with acute abstinence from smoking. (Mendrek, Monterosso, Simon, Jarvik, Brody et al, 2006).
The studies on the impact of abstinence upon cognition aims at the impact of abstinence from smoking on a relatively short period of time, often from a few minutes to several hours, and in some cases a few weeks. These studies have found evidence of a range of psychological changes, including irritability, poor concentration, restlessness or cigarette craving (Parrott and Garnham, 1998). A number of these studies have found deficits in cognitive performance when tested during the abstinent periods. Hendricks, Ditre, Drobes and Brandon, (2006) found attentional problems emerging from 30 minutes of abstinence, while Jacobson et al., (2005) also found that abstinent smokers suffered acute impairment in verbal memory (word recall) and working memory (using the N-back procedure) (Jacobson, Mencl, Constable, Westerveld and Pugh, 2005; Jacobson et.al, 2007).
Therefore, based on the above literature review the hypothesis stating that “The score on attentional deficits will be significantly higher among nicotine dependents than non- nicotine dependents” was formulated.
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