mental fatigue is common and can be a disabling long - time condition following a stroke .
it has been estimated that about 3070% of stroke survivors complain of fatigue [ 17 ] . even for those with an almost recovered stroke and without neurological and neuropsychological impairments ,
the person who suffers from mental fatigue is able to perform mental effort just for short periods , and , notably , it will take longer than normal to regain energy after being exhausted . accompanying symptoms , such as irritability , sensitivity to stress , concentration difficulties , and emotional instability may further impair social interactions [ 811 ] .
however , attention has been paid to poststroke fatigue during the last 10 years , and fatigue is now generally held as a separate phenomenon [ 46 , 1214 ] .
few investigations have been carried out to evaluate fatigue and cognitive functions following a stroke .
leegard reported that fatigue is frequent following a stroke but did not find any related impaired cognitive functions .
van zandvoort and coauthors investigated lacunar infarct and reported frequent difficulties relating to fatigue and a decreased cognitive performance under more demanding conditions . with the intention to increase knowledge about mental fatigue and cognitive difficulties related to stroke
, we examined well - rehabilitated stroke participants , who had suffered from long - term mental fatigue for at least one year prior to examination .
the subjects were examined for subjective self - reporting of mental fatigue , depression , and anxiety symptoms .
neuropsychological tests were aimed at evaluating information processing speed , attention , and working memory .
twenty - four participants , having recovered from neurological symptoms , but suffering from pathological mental fatigue for at least one year following a stroke and 24 healthy controls were included in the study .
the study persons were recruited from an advertisement in a local , daily newspaper or from the neurological clinic at the local university hospital and were later included in intervention studies .
the stroke subjects should have been healthy and at work before the stroke meaning that they had no known diseases but hypertonia was present among some participants .
the type of stroke was obtained from medical records and self - reports ( see table 1 ) .
the control participants were recruited from the local community , with no history of brain injury , stroke , psychiatric or neurological disorder , and no drug abuse , and they were fully able to work .
they performed cognitive tests focused on information processing speed , attention , and working memory .
the self - assessment for mental fatigue is a multidimensional questionnaire containing 15 questions and is adapted from rdholm et al . .
the self - reported questionnaire covers the most common symptoms occurring after brain injury , stroke , or other neurological disorders affecting the brain [ 11 , 17 ] .
the self - assessment scale for mental fatigue and related items has been evaluated , and the 14 questions had adequate internal consistency with a cronbach 's alpha of 0.94 .
the questions concern fatigue in general , lack of initiative , mental fatigue , mental recovery , concentration difficulties , memory problems , slowness of thinking , sensitivity to stress , increased tendency to become emotional , irritability , sensitivity to light and noise , and decreased or increased duration of sleep as well as 24-hour variations .
this cprs scale is used here for self - assessment of depression and anxiety .  
the neuropsychological tests included digit symbol - coding from the wais - iii , measuring information processing speed , digit span from the wais - iii , measuring attention and working memory ; verbal fluency test , fas ; trail making test ( tmt ) a and b , measuring visual scanning , divided attention and motor speed . in order to evaluate higher demands such as dual tasks ,
a series of two new trail making tests was constructed with three and four factors , respectively .
months were added in part c and both months and days of the week in chronological order in part d. in the latter , the order of letters and digits was switched .
a new computer test was constructed in our department including a single and a complex subtest .
the single test included speed of mouse click in four squares , located in each corner of a bigger square ( 6  6  cm ) on the computer screen and was performed in a clockwise order .
a mouse click outside the square was recorded as a miss , and a new click was necessary to do in order to be able to go on with the test .
the complex sub - test also included the same mouse clicking procedure , but at the same time , the subject was asked to count how many instances of a specific digit between zero and nine , randomly chosen , he / she could see .
after the 30 seconds , the subject was asked to report how many of the specific digit he / she had seen .
it was possible to measure the difference in speed between a single and a complex task , variability over time , and errors made in counting digits . in the complex test , it was necessary to attend to both the square and the digits .  
a comparison between groups was done by t - test and analysis of covariance ( ancova ) .
the mann - whitney u test was used when analyzing separate items included in the self - assessment scales .
pearson 's correlation and linear regression were used for analysis of connections between variables . spss 16.0 for windows
the control group had significantly more years of education than the stroke group ( t - test , p = 0.001 ) , and age was almost significantly different when comparing the two groups ( p = 0.055 , table 1 ) .
accordingly , ancova , controlling for the variance for education and age , was conducted for all the variables analysed .
the only significant gender difference found was that the control females were faster in the digit symbol - coding test , and an ancova , also controlling for sex , was conducted for this variable .
a significant difference was found between the groups for the total sum of scores for mental fatigue .
the mean value for the stroke group was 18.4 with a 95% confidence interval of between 16.420.5 .
the mean value for the control group was 4.0 , with a 95% confidence interval of between 2.95.0 ( see figure 1 ) .
the total score for the cprs scale , taken from the depression and anxiety subscale , was also rated significantly higher in the stroke group compared to controls ( see table 2 , figure 1 ) . the significant effect for mental fatigue remained after adjustment for depression ( p < 0.001 ) .
all the separate items in the self - assessment scale for mental fatigue were rated significantly higher for the stroke group compared to controls .
the cprs gave the following findings : without taking into account overlapping items , the items relating to sadness , emotional involvement , pessimistic thoughts , and zest for life rated significantly higher for the stroke group ( adjusted for multiple comparisons , as shown in figure 2 ) . among the stroke subjects ,
74% reported a clear 24-hour variation with morning most frequently reported to be the best time of the day and afternoon and evening the worst .
the participants from the stroke group were significantly slower on the test measuring information processing speed , primarily digit symbol - coding , and also reading speed and number of mouse clicks in the computer test .
the stroke group was also significantly slower and made more errors in tmt d , the most demanding of the tmt tests .
they were also significantly slower on tmt b , and produced fewer words on the verbal fluency test .
the result for the simple mouse click sub - test was found to be significantly faster for the controls compared with the stroke subjects . the computer test which placed a simultaneous demand on speed , attention , and working memory , resulted in a fairly good speed for the stroke subjects , with no detected difference in speed compared to the controls . on the contrary , the stroke subjects made significantly more errors compared to the controls ( table 2 , figure 3 ) .  
the cognitive tests with significant results ( p < 0.05 , see table 2 ) were included in a linear regression model , using the enter method .
digit symbol - coding ( p = 0.004 ) and the scores for number of errors in the computer test ( p = 0.018 ) were significant predictors for mental fatigue , while the other scores were not significant predictors for mental fatigue .
digit symbol - coding and number of errors in the computer test also correlated significantly to the mental fatigue sum of scores ( r = 0.59 and r = 0.46 ) .
the total scores for cprs , depression , and anxiety were on a significantly higher level compared to controls .
the madrs , which provides a separate scale , has the same format as the cprs self - assessment scale depression , except that the items are graded in a different way . in the cprs scale ,
depression , the highest level is three for each separate cprs item , while the levels for the alternatives in the madrs scale are double for each separate item , with the highest level being 6 . according to madrs
, a score between 12 and 20 is regarded as mild depression and 21 and above indicates a probable true depression .
the mean level of eight for the stroke subjects corresponds to 16 on madrs , indicating an overall mild level of depression .
there was a highly significant difference between the groups on their self - assessment of mental fatigue , with a mean value of 18 reported for the almost recovered stroke group and a mean value of four for the control group .
the self - assessment scale has no cut - off value for fatigue , but our experience shows that a value of 15 and above indicates a clear problem with mental fatigue [ 9 , 23 ] . the clear difference in 24-hour variation also showed the specific exhaustion mental fatigue subjects experience during the active time of the day .
it should be noticed that stroke victims were included due to the presence of mental fatigue during one year or more following the stroke .
the data we have presented in our study do not include an indication of the frequency of mental fatigue after different types of stroke .
however , on an individual basis , according to madrs , eight participants were not depressed , seven had an indicated mild depression , and nine had a probable , true depression . among the controls , two participants scored on a mild depression level , while the remainder scored below this level .
the total sum of scores on the depression scales may be deceptive if a person is complaining of concentration difficulties and fatigue , but does not have a depressed mood , nor a lack of interest in and enjoyment of daily activities . in this study
, three items were overlapping between mental fatigue and depression , and these items were rated on a higher level than the corresponding specific items on the depression sub - scale ( see figure 2 ) .
depression and mental fatigue can occur on their own , but they sometimes occur simultaneously , as shown in this study . accordingly , we suggest mental fatigue and depression to be independent phenomena following a stroke .
this also conforms with the findings from other studies [ 46 , 12 , 13 ] .   the distressing exhaustion along with the bad memory , concentration difficulties , and not being able to perform simultaneous tasks are the phenomena many subjectively complain of following a stroke .
it is important to include cognitive tests in the examinations in order to better understand the difficulties connected to mental fatigue and for the purpose of recommending treatment strategies . in this study ,
physically well - recovered stroke subjects , who had no medical problems except long - term mental fatigue , also showed decreased information processing speed and made more errors in demanding cognitive tasks compared to the control subjects .
processing speed is also fundamental and important when considering cognitive functions of a higher order .
few studies have been carried out which cover fatigue and cognitive performance following a stroke .
however , studies have shown the connection between fatigue and decreased cognitive performance under more demanding conditions , while no cognitive impairments were detected , despite frequent fatigue . with more demanding and sensitive tests , including processing speed and complex attention , it may be possible to detect cognitive impairments accompanying mental fatigue .
this is important , as mental fatigue and cognitive deficits will be an obstacle to almost recovered stroke subjects who are on their way to a return to work and previous activities , as every - day life today is complex , with high demands being placed on simultaneous and rapid decisions . in conclusion , mental fatigue is disabling for many people following an almost recovered stroke , and this is suggested to be related to cognitive impairments , primarily information processing speed , and attention .
mental fatigue should also be treated as a separate phenomenon and should be differentiated from , and not confused with , depression .
today , no specific guidelines exist for the treatment of mental fatigue , and research is urgently needed for this common yet distressing symptom .
 mental fatigue is for many a distressing and long - term problem after stroke . 
 this mental fatigue will make it more difficult for the person to return to work and previous activities . 
 the intention with this study is to investigate mental fatigue in relation to depression and cognitive functions . 
 we examined 24 well - rehabilitated stroke subjects , who suffered from mental fatigue one year or more after a stroke , and 24 healthy controls . 
 subjects were examined using self - assessment scales for mental fatigue , depression and anxiety , and cognitive tests . 
 the results showed a highly increased rating for mental fatigue for the stroke group ( p < 0.001 ) . 
 these participants also had a significantly higher rating on the depression ( p < 0.001 ) and anxiety ( p < 0.001 ) scales . 
 furthermore , they had a slower information processing speed ( p < 0.001 ) and made more errors in a demanding attention and speed test ( p < 0.05 ) . among the cognitive tests , processing speed and errors made in an attention and speed test were significant predictors for mental fatigue . 
 we suggest mental fatigue following a stroke to be related to cognitive impairments , primarily information processing speed . 
 mental fatigue should also be treated as a separate phenomenon and should be differentiated from , and not confused with , depression , even if overlapping symptoms exist . 
1. Background
2. Materials and Methods
3. Results 
4. Discussion