Table 2

Raw cognitive test scores at baseline and change scores at 3 weeks and 8 month follow-up for the DBS and control group

Group, mean ± SD
Test score*DBSControlStatisticp value†Cohen d‡
Memory
 California Verbal Learning Test
  Total recall in 5 trials52.9 ± 10.857.8 ± 11.9
  Change score 3 weeks−1.9 ± 6.90.5 ± 5.5t28 = −1.080.28−0.4
  Change score 8 months2.5 ± 6.64.6 ± 8.9t28 = −0.580.57−0.3
  Stability of timet27 = 0.100.92
 Digit span
  Forward9.3 ± 1.99.5 ± 2.0
   Change score 3 weeks0.2 ± 1.70 ± 2.1t27 = 0.170.870.1
   Change score 8 months−0.3 ± 1.8−0.2 ± 2.4t27 = −0.140.89−0.1
   Stability of timet27 = −0.300.77
  Backward5.7 ± 1.56.6 ± 2.1
   Change score 3 weeks1.4 ± 1.60.4 ± 1.4t27 = 1.140.260.7
   Change score 8 months1.0 ± 1.90.9 ± 2.0t29 = −0.190.850.1
   Stability of timet28 = −1.170.25
 Rey Complex Figure Test
  Copy score31.6 ± 2.730.9 ± 4.1
   Change score 3 weeks−1.7 ± 1.91.7 ± 3.7t27 = −3.640.001−1.2
   Change score 8 months−2.3 ± 3.12.6 ± 4.3t28 = −3.920.001−1.3
   Stability of timet28 = −1.590.11
  Immediate recall score21.6 ± 7.619.9 ± 6.3
   Change score 3 weeks−1.8 ± 5.93.1 ± 5.0t28 = −2.20.030−0.9
   Change score 8 months0.4 ± 4.46.4 ± 4.7t27 = −3.750.001−1.3
   Stability of timet28 = −0.520.60
Executive functioning
 Stroop Colour Word Test
  Time card 3 – time card 2 seconds44.0 ± 22.432.9 ± 11.8
   Change score 3 weeks−6.5 ± 14.1−3.6 ± 7.9t27 = 0.430.67−0.3
   Change score 8 months−7.6 ± 15.8−3.2 ± 11.6t28 = 0> 0.99−0.3
   Stability of timet28 = −0.390.70
 Verbal fluency
  Phonemic (A)11.8 ± 3.811.0 ± 4.9
   Change score 3 weeks−1.8 ± 2.4−0.2 ± 4.8t27 = −1.100.27−0.4
   Change score 8 months−0.6 ± 3.01.9 ± 4.5t28 = −1.610.11−0.7
   Stability of timet28 = −0.750.46
  Phonemic (N)11.9 ± 4.213.4 ± 3.5
   Change score 3 weeks−2.0 ± 4.4−1.6 ± 3.5t28 = −0.870.38−0.1
   Change score 8 months−0.1 ± 3.8−0.1 ± 4.5t28 = −0.480.630
   Stability of timet28 = 0.250.80
  Semantic (animals)22.3 ± 5.623.3 ± 5.5
   Change score 3 weeks−1.5 ± 5.20.5 ± 3.8t27 = −1.660.10−0.4
   Change score 8 months−0.7 ± 4.50.2 ± 4.2t27 = −0.680.50−0.2
   Stability of timet28 = 0.580.56
 Semantic (occupations)15.6 ± 2.914.8 ± 3.5
  Change score 3 weeks−0.9 ± 3.92.9 ± 2.5t27 = −3.040.002−1.2
  Change score 8 months3.1 ± 3.5−0.5 ± 4.0t27 = −0.030.981.0
  Stability of timet28 = 2.280.025
 Trail Making Test
  Time B ÷ time A2.0 ± 0.42.2 ± 0.7
   Change score 3 weeks0.6 ± 0.80.1 ± 0.7t28 = 1.310.190.7
   Change score 8 months0.8 ± 1.6−0.2 ± 0.6t29 = 1.910.060.8
   Stability of timet28 = 1.080.28
 Wisconsin Card Sorting Test
  No. of categories4.4 ± 2.15.1 ± 1.9
   Change score 3 weeks−0.6 ± 2.1−0.5 ± 1.6t28 = −0.240.65−0.1
   Change score 8 months0.1 ± 1.70.1 ± 1.2t28 = −0.340.740
   Stability of timet28 = 0.120.90
  % of perseverative errors19.9 ± 17.813.6 ± 11.1
   Change score 3 weeks−1.8 ± 12.52.4 ± 12.5t28 = −0.180.86−0.3
   Change score 8 months−4.0 ± 8.4−2.7 ± 12.0t27 = 0.540.59−0.1
   Stability of timet28 = 0.780.44
 Tower of London Test
  Total no. of steps32.6 ± 5.532.2 ± 5.1
   Change score 3 weeks−2.1 ± 5.60.7 ± 8.0t27 = −1.010.31−0.4
   Change score 8 months−2.0 ± 7.23.9 ± 7.7t27 = −1.890.07−0.8
   Stability of timet28 = −0.900.38
 Raven Advanced Progressive Matrices9.2 ± 1.78.4 ± 3.0
  Change score 3 weeks−0.8 ± 1.90.6 ± 1.7t27 = −1.970.05−0.8
  Change score 8 months−0.4 ± 2.50.5 ± 2.4t28 = −0.740.46−0.4
  Stability of timet28 = 0.530.60
Attention
 Continuous Performance Test
  Figures d-prime1.7 ± 0.71.6 ± 0.7
   Change score 3 weeks−0.1 ± 0.70.5 ± 0.9t26 = −1.840.07−0.7
   Change score 8 months0 ± 0.50.4 ± 0.7t26 = −1.160.26−0.7
   Stability of timet28 = 0.580.57
  Figures Log-B0.4 ± 0.8−0.2 ± 0.9
   Change score 3 weeks−0.1 ± 0.90.1 ± 1.0t28 = 1.240.22−0.2
   Change score 8 months−0.2 ± 1.00 ± 1.1t27 = 1.050.30−0.2
   Stability of timet28 = −0.140.89
 Digit Symbol Substitution Test
  No. of digits63.5 ± 11.168.7 ± 16.4
   Change score 3 weeks2.9 ± 5.61.1 ± 10.1t27 = 1.040.300.2
   Change score 8 months6.5 ± 7.42.7 ± 10.0t28 = 1.330.190.4
   Stability of timet28 = 0.670.52
Motor system
 Purdue Pegboard
  Dominant hand14.1 ± 1.713.5 ± 2.3
   Change score 3 weeks−0.2 ± 1.90.7 ± 1.9t27 = −1.20.23−0.5
   Change score 8 months−0.3 ± 1.40.3 ± 1.4t27 = −0.630.54−0.4
   Stability of timet28 = 0.500.62
  Nondominant hand13.2 ± 2.612.8 ± 1.7
   Change score 3 weeks0.4 ± 1.60.2 ± 1.6t27 = 0.620.540.1
   Change score 8 months0.5 ± 2.41.4 ± 1.9t28 = −0.940.35−0.4
   Stability of timet28 = −1.300.20

  • DBS = deep brain stimulation; SD = standard deviation.

  • ↵* Change score at 3 weeks was defined as the score at 3 weeks postoperative – baseline score. Change score at 8 months was defined as the score at 8 months postoperative – baseline score. Negative change scores indicate decline in performance except for test variables assessing speed and error scores (Stroop Colour Word Test; Trail Making Test; Wisconsin Card Sorting Test, % perseverative errors).

  • ↵† A significant p value at 3 weeks refers to an effect of the intervention at 3 weeks. A significant p value at stability of time refers to an effect of the intervention at 8 months. A nonsignificant p value at stability of time with a significant p value at 3 weeks refers to an effect from the intervention at 3 weeks that is still present at 8 months. The p values were corrected for differences at baseline.

  • ↵‡ The effect size (Cohen d) is negative if the DBS group shows more decline in performance on this variable than the control group, or positive if the DBS group shows more improvement, except for the test variables assessing speed and for error scores.