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April2015 Vol.52 Issue:      2 Table of Contents
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Quantitative Electroencephalographic and Psychometric Analysis of Possible Cognitive Decline in Healthy Elderly Subjects

Ann A. Abdel Kader1 , Ebtesam M. Fahmy2, Ayatallah F. Ahmed1, Omneya Raafat3, Amira A. Labib1, Alshaimaa S. Khalil1

Departments of Clinical Neurophysiology1, Neurology2, Psychiatry3, Cairo University; Egypt



ABSTRACT

Background: Numerous studies have been done to investigate aging and age-related changes (ARCs) which refer to the deterioration in the biologic processes occurring with senescence and lead to impaired brain structure, cognitive performance and behavior. Objectives: To assess cognitive functions in normal elderly subjects using power of brain activity and psychometric cognitive assessment scales. Methods: Forty seven healthy elderly subjects were assessed with quantitative electroencephalography and psychometric scales. Results: There was a significant positive correlation between relative power of alpha frequency and the total score of performance scale of Wechsler Intelligence scale (WIS). No significant correlation was revealed between relative power of EEG frequencies and scores of WMS subtests and parameters of WCST. Conclusion: Results suggest that the psychiatric scales do not provide a substitute for electrophysiological tests in evaluating the cognitive changes which occur with normal aging. However, there was a limitation in the study caused by the narrow age range of the cases. [Egypt J Neurol Psychiat Neurosurg.  2015; 52(2): 87-94]

 

Key Words: cognitive, electrophysiological, psychometric, electroencephalography, aging.

Correspondence to Amira Ahmed Labib, Department of Neurophysiology, Cairo University, Egypt.

 Tel.: +201222588149.  Email: amiralabib2@gmail.com





INTRODUCTION

 

Studies concerned with cognitive functions of geriatrics have shown that cognitive performance declines with age; this includes executive functioning, episodic memory and processing speed1,2.

An electroencephalography (EEG) is the recording of the electrical potential generated in the brain3, 4. Digital EEG is the paperless acquisition and recording of the EEG via computer-based instrumentation5. Topographic EEG displays can present visually a spatial representation of raw EEG data (i.e., voltage amplitude) or a derived parameter (e.g., power in a given frequency band, or peak latency)6. Electroencephalographic activity is accompanied by sensory and cognitive processing of information, which is dependent on neocortical function7.

Many studies have reported changes in the EEG related to aging and showed a relationship between specific changes in the EEG and clinical deterioration8. Quantitative Electroencephalography (QEEG) has been nominated as a sensitive indicator of diseases such as mild cognitive impairment and Alzheimer’s disease 9. However, few ones have studied the relationship between QEEG and the cognitive function in healthy elderly individuals10.

This study aimed to assess cognitive functions in normal elderly subjects using brain mapping and psychometric assessment battery.

 

SUBJECTS AND METHODS

 

Study Design:

This is a case-control study carried out on 47 healthy elderly subjects. They were recruited from relatives of the workers, nursing staff and patients admitted in the neurology department, Cairo University Hospitals, in the period from February 2012 to September 2013.

 

Patients:

All subjects were above 60 years old, with normal neurological examination. normal CT or MRI brain and normal hearing. Their mini-mental state score exceeded 24 and Hamilton depression scale score exceeded 7 and had variable levels of education. Excluded from the study illiterate subjects, those with profound psychological problems or with diminished hearing.

 

Methods:

All participants were submitted to the following:

A.     Thorough clinical assessment including careful general medical assessment and complete neurological examination.

B.     Routine laboratory investigations: fasting and post prandial blood sugar level, lipid profile, liver and kidney function tests, complete blood count, ESR, uric acid, Na, K & calcium levels.  These tests were done for exclusion of  any systemic diseases.

C.     Brain imaging (CT or non-contrast MRI):This was performed at the department of diagnostic radiology, to exclude any organic brain lesions.

D.     Cognitive assessment using the following neuropsychological tests: the Wechsler Adult Intelligence Scale (WAIS), the Wechsler Memory Scale (WMS) and the Wisconsin Card Sorting Test (WCST).

E.     Digital EEG examination: Digital EEG examination was performed at the clinical neurophysiology unit, Cairo University Hospitals. The scalp EEG electrodes were applied according to the International 10-20 electrode placement system. All studies included bipolar; anterior-posterior, transverse, and unipolar; referential montages.

 

In a separate control room, the video EEG was continuously monitored by a technologist utilizing a Schwartzer® video-electroencephalograph system with a Brainlab 4 ® software. The high frequency filter was 70 Hz, the time constant 0.3, paper speed 30 mm /sec and the sampling rate was 250. Provocation procedures included: Intermittent photic stimulation and three minutes of hyperventilation, whenever possible. Interpretation of the EEGs was done by visual inspection of concurrent split-screen video and EEG, including review of all activation procedures. Epochs were selected for QEEG while awake and resting (free from eye movement artifacts). The absolute and relative powers of 19 electrodes (Fp1, Fp2, F7, F8, F3, F4, C3,C4, T3, T4, T5, T6, P3, P4, O1, O2, Fz, Cz and Pz) were studied in the following frequency bands: delta (1-3Hz), theta (4-7 Hz), alpha (8-12 Hz) & beta (13-30 Hz). Relative power was represented by the percentage of the amplitude in a given frequency band compared with the total amplitude across all frequency bands. Relative delta power, for example, is equal to (absolute delta power/absolute delta power + absolute theta power + absolute alpha power) * 100. The theta-delta/alpha-beta power ratio was calculated.

 

Statistical Methods

Data were analyzed using SPSSwin (Statistical Package for Social Science), version 20. Numerical data were expressed as means and standard deviations or medians and ranges as appropriate. Regarding quantitative variables, comparison between two groups was done using student t-test. Bivariate correlation analysis was done to assess correlation between age & different variables in either neurophysiological test or Psychometric tests.  Pearson correlation coefficient was used and correlation was significant at 0.05 level or 0.01 level, according to comparisons after Banfaroni adjustment.  A P-value less than 0.05 was considered significant. Trend-wise significance was considered for a value less than 0.08 and greater than 0.05.

 

RESULTS

 

General Characteristics of the Study Population:

This study was carried out on 47 healthy elderly subjects. Subjects included 24 males (51%) and 23 females (49%). Their ages ranged between 60 and 78 years with a mean age of 65.4 (±4.1) years. Thirty subjects (63.8%) had 6 years of compulsory formal primary education, fifteen subjects (31.9%) were high school graduates and two subjects (4.2%) were graduates from universities. They were all right-handed. They had normal general and neurological examination.

 

Results of the Neurophysiological Studies:

Concerning brain mapping, the mean values of relative power of beta, alpha, theta and delta frequencies at frontal, temporal and occipital regions are shown in Table (1).

 

Results of the Psychometric Scales:

-              Wechsler Intelligence Scale (WIS).

-              Wechsler Memory Scale (WMS).

-              Wisconsin Card Sorting Test (WCST).

 

The minimum, maximum and mean scores of the used psychometric tests are represented in Tables (2-4).

 

v    Comparisons:

-        Male group: 24 males, ages ranged from 60-73 years with a mean of 64.25±3.35 years.

-        Female group: 23 females, ages ranged from 60-78 years with a mean of 66.6±4.5 yrs.

-        No statistically significant difference was observed between both groups regarding mean age (P=0.99).

i.       Different relative power frequencies of EEG between male and female groups: Comparison of mean relative power of EEG frequencies recorded from the frontal, temporal and occipital regions showed that the mean relative power of theta frequency recorded from frontal and occipital regions among females were significantly higher than those recorded from the same region among males (P=0.005, 0.01; respectively). There is a trend-wise significant increase in the relative power of theta frequency recorded from temporal region in females compared to males (P=0.06). The mean relative power of the alpha frequency recorded from the temporal region was significantly higher in males compared to females (P=0.03). Otherwise, no significant difference was recorded between male and female subjects regarding other EEG relative power frequencies (P>0.05) (Figure 1).

ii       WIS scores: Comparison of mean WIS parameters recorded from males and females showed that the mean score of vocabulary subtest and the total score of the performance scale were significantly higher among males compared to females (P= 0.03, 0.04; respectively). In addition, there was trend-wise significant increase of the total score of the verbal scale among males compared to females (P=0.07). Otherwise, no significant difference was noted between male and female subjects regarding other WIS subtest scores (P>0.05) (Figure 2).

iii.     WMS scores: Comparison of mean scores of different WMS subtests revealed no significant difference between male and female subjects (P>0.05).

iv.     WCST scores: Comparison of scores of WCST parameters revealed no significant difference between male and female subjects (P>0.05).

 

v    Correlations:

[1]    Correlations of Quantitative EEG and neuropsychological parameters with age:

i.       Relative power of frequencies of EEG: A significant positive correlation was noted between age and relative power of theta frequency recorded from the frontal and occipital regions (P=0.01) (Figure 3).

ii.      Ratio recorded from frontal, temporal and occipital regions: No significant correlation was found between ratio (frontal, temporal and occipital) and age (P>0.05).

iii.     WIS, WMS and WCST scores: No significant correlation was revealed between age and mean scores of WIS or WMS subtests (P>0.05), however a significant positive trend-wise correlation was found between mean value of preservative runs and age (P=0.06).

[2]    Correlations between Quantitative EEG and psychometric scales:

i.       Correlation of relative power of EEG frequencies with WIS, WMS and WCST scores: A significant positive correlation was noted between alpha relative power recorded from frontal and occipital regions and performance scale in WIS subtest score (P=0.04), otherwise, no significant correlations were detected (P>0.05).

ii.      Correlation of ratio with parameters of WIS, WMS and WCST: No significant correlation was found between ratio recorded from frontal, temporal and occipital regions and the mean values of parameters of each test. (P>0.05).


 

Table 1. Values of different relative powers of frequencies of Quantitative EEG in the study population.

 

Variable

N

Minimum

Maximum

Mean

SD

Beta

frontal

47

17.4

163.86

64.09

36.31

temporal

47

26.9

236

87.05

46.42

occipital

47

6.2

107.94

32.60

25.35

Alpha

frontal

47

2.9

59.0

19.17

13.98

temporal

47

5.0

61.0

22.27

13.25

occipital

47

4.2

70.3

26.77

16.58

Theta

frontal

47

5.6

39.6

14.71

7.52

temporal

47

6.0

36.6

15.29

7.83

occipital

47

4.0

44.5

15.83

11.06

Delta

frontal

47

12.0

81.4

53.45

14.97

temporal

47

13.4

73.4

50.08

13.17

occipital

47

10.0

81.0

41.08

17.31

Table 2. Minimum, maximum and mean scores of WIS subtests among the study population.

 

Variable

N

Minimum

Maximum

Mean

SD

Information

47

7

10

8.16

1.04

Comprehension

47

6

14

8.31

1.52

Arithmetic

47

6

9

7.07

0.96

Digit span

47

6

11

7.58

1.05

Similarities

47

6

9

6.87

0.92

Vocabulary

47

6

9

7.71

1.18

Total score of the Verbal scale

47

38

58

45.87

4.11

Picture arrangements

47

5

9

7.07

1.21

Picture completion

47

3

12

6.02

1.57

Block design

47

5

9

6.80

1.7

Object assembly

47

6

13

8.18

1.94

Coding digit symbol

47

6

10

7.82

1.26

Total score of the Performance scale

47

28

47

35.87

4.31

 

Table 3. Minimum, maximum and mean scores of WMS subtests among the study population.

 

Variable

N

Minimum

Maximum

Mean

SD

Information

47

4

6

5.42

0.92

Orientation

47

4

6

4.80

0.78

Mental control

47

3

6

4.73

1.27

Memory

47

5

12

7.71

2.23

Digits total

47

8

11

8.64

1.02

Visual reproduction

47

0

8

5.58

2.52

Associate

47

8

12

9.67

1.08

 

Table 4. Minimum, maximum and mean scores of WCST parameters among the study population.

 

Variable

N

Minimum

Maximum

Mean

SD

Categories completed

47

0

0.83

0.60

0.24

Correct responses

47

59

83

70.0

7.81

Total errors

47

40

69

57.42

8.16

Perseverative responses

47

0

69

39.91

22.57

Perseverative errors

47

0

75

25.82

17.65

Non perseverative errors

47

7

69

33.49

19.49

Unique errors

47

0

39

9.33

10.19

Trials to complete 1st set

47

0

75

32.76

28.68

Perseverative runs-mean

47

0

12.00

3.58

3.17

Perseverative runs-total

47

0

24

10.24

8.99

 

 

 

Figure 1. Comparison of relative power of frequencies of EEG between male and female normal elderly subjects.

 

 

 

Figure 2. Comparison of Verbal scale of WIS subtests between male and female normal elderly subjects.

 

 

 

Figure 3. Correlation of age and relative power of theta frequency in normal elderly subjects.

 

 

 


DISCUSSION

 

Aging has deleterious effects on cognitive processes, particularly memory for personally experienced recent episodes and executive control processes10. This has been related to changes in brain structure and function, which mostly affect the prefrontal cortex and the hippocampus11. Significantly, however, there is a large scale of heterogeneity in cognitive performance among elderly healthy people. Actually, inter-individual variability in task performance increases as people get older12.

The present study aimed to assess cognitive functions in normal elderly subjects using psychometric cognitive assessment scales and electrophysiological studies of the brain activity. We used the relative power of EEG frequency bands, as the variability of the absolute power is higher than the variability of the relative power, and so the relative is more sensitive. It was found that the mean relative power of theta frequency recorded from frontal and occipital regions among females was significantly higher than those recorded from the same region among males. Relative power of theta frequency recorded from temporal region showed trend-wise increased significance in females compared to males. In addition, relative power of alpha frequency recorded from temporal region was significantly higher in males compared to female subjects. Regarding the rest of EEG frequencies, no statistically significant difference was detected between males and females. This was partially in agreement with Veldhuizen et al.13, who reported several spectral differences, including increased relative beta and theta power in women, whereas alpha was higher in men. Dustman et al. 14 did not demonstrate gender differences for absolute EEG power in healthy normal elderly peoples. Giaquinto and Nolle15 and Williamson et al. 16reported increased beta activity in elderly women compared to men. Giaquinto and Nolle15 also reported less delta activity in women. Some authors stated that the reasons for spectral gender-related differences are unknown. Others related this difference to sex differences in brain anatomy and chemistry, and in certain aspects of brain development17,18. Female brains have smaller volumes and approximately 16% fewer neocortical neurons at any age than male brains19. However, many studies have reported more substantial age-related atrophy or reductions in brain volume in males than in females20,21 yet some have suggested earlier onset or more severe atrophy in females22,23. It is generally found that a larger percentage of the total volume is occupied by gray matter in females than in males18.

 

A significant positive correlation was noted between age and relative power of theta frequency recorded from the frontal and occipital regions. This partially goes with Prichep et al.7 who found an excess of theta and delta absolute power and theta relative power, along with a deficit of beta relative power in healthy elderly subjects. Also, Computerized EEG demonstrated decrease in alpha activity in elderly, in males, and in non-educated subjects. However, significant increase in theta activity was detected only in the subgroup of non-educated subjects. Elderly subjects did not show increase in theta activity. Quantitative spectral analysis interestingly revealed either no increase in slow activity or even a decrease in all frequency bands24,25. Increase in slow activity in normal subjects was linked to cognitive impairment in advancing age26.

On correlating relative power of different EEG frequencies with WIS subtests scores, a significant positive correlation was noted between alpha relative power recorded from frontal and occipital regions and performance scale. This is in agreement with Roca-Stappung et al.9, who hypothesized that low delta and theta activity and/or high alpha and beta activity would be correlated with better performance on the WAIS-III in healthy elderly subjects. This suggests that some WAIS-III subtests may be valuable as a brain function indicator. High scores on verbal and performance indices could discount brain function deterioration. A significant correlation does not necessarily imply cause and effect, and therefore, scores of WAIS-III subtests should not be substituted for EEG measurements. They may, however, add value to EEGs as important indicators of future cognitive decline.

No significant correlation was found between relative power of different EEG frequencies and scores of WMS subtests and parameters of WCST. This may indicate that aging effect on EEG does not reflect cognitive decline in psychometric tests.

On correlating age and ratio of the frontal, temporal and occipital regions, no significant correlation was found. Also, on correlating ratio with the parameters of the 3 psychometric tests, no significant changes in cognitive functions have been found.

In conclusion, we can suggest that the psychiatric scales do not provide a substitute for electrophysiological tests in evaluating the cognitive changes, which occur with normal aging.

 

[Disclosure: Authors report no conflict of interest]

 

 

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الملخص العربي

 

أجريت دراسات عديدة على تقدم السن والتغيرات المرتبطة بالعمر والتي تشير إلى انخفاض الأداء الأمثل في العمليات البيولوجية التي تحدث مع الشيخوخة و تؤدي إلى ضعف بنية الدماغ، والأداء المعرفي والسلوك.هدفت هذه الدراسة إلى تقييم الوظائف المعرفية في تقدم السن الطبيعي باستخدام القياس النفسي ورسم المخ الكمى بما في ذلك قوة نشاط الدماغ. وقد أجريت الدراسة على 47 مسنا من الأصحاء, تراوحت أعمارهم بين 60 و 78 عاما مع متوسط ​​عمر 65.4 (±4.1) سنة. وشملت عينة الدراسة 24 من الذكور (51٪) و 23 من الإناث (49٪). كانت القوة النسبية للتردد ثيتا أعلى بفارق بين الإناث أكثر من الذكور في حين كانت القوة النسبية ألفا أكبر بين الذكور. ارتبطت القوة النسبية للتردد ثيتا إيجابيا مع تقدم العمر. وقد لوحظ علاقة إيجابية ذات دلالة إحصائية بين القوة النسبية تردد ألفا السلطة والدرجة الكلية لمقياس الأداء في اختبار ويكسلر للذكاء. بينما وجد عدم وجود ارتباط كبير بين القوة النسبية للترددات في خرائط المخ واختبار ويكسلر للذاكرة واختبار ويسكنسن لترتيب البطاقات. في ضوء النتائج التي توصلنا  إليها؛ خلصنا الى ان هذه النتائج تدعم فكرة أن المقاييس النفسية لا تقدم بديلا عن الاختبارات الكهروفسيولوجية في تقييم التغيرات المعرفية التي تحدث مع الشيخوخة الطبيعية. ومع ذلك، كان هناك قيود في هذه الدراسة وهي ضيق مساحة الفئة العمرية محل البحث.

 



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