## 2 Methods
### Measures
#### 2.2.4 Neuropsychological Tests  
Multiple neuropsychological tests were administered before the training program (T0), after three weeks (T1), and after six weeks (T2). The test battery included tests for general cognition (screening), working memory, long-term memory, and executive functioning. During the midterm testing (T1), only the screening tool for general cognition was given, because completing the full test battery three times was too straining and time-intensive for patients. When possible, parallel test versions were used at the different test sessions (i.e., MoCA and RAVLT).  
_General Cognition Screening_. To measure general cognition, the Dutch parallel version of the Montreal Cognitive Assessment (MoCA) was given (7.1, 7.2, 7.3) [37]. The MoCa is a short cognitive screening test with high sensitivity and specificity. It is a 30-point test consisting of several short tasks measuring different cognitive domains. The instrument has successfully been applied to detect KS-related cognitive deficits [38].  
_Working Memory_. A lengthened Dutch version of the Digit Span subtest from the Wechsler Adult Intelligence Scale, version III was used to measure verbal working memory [39]. This version consists of two parts in which patients have to remember and repeat a verbally presented digit span. The digit spans increase in length after every three items. During the first part, the participant has to repeat sequences of digits in the same order that is presented to them verbally. In the second part, the participant has to repeat the sequences backwards. The test is finished when the participant is not able to repeat two consecutive sequences of the same length correctly. A higher score represents a better working memory capacity.  
_Long-term Memory_. Verbal long-term memory was measured using the Dutch version of the Rey Auditory Verbal Learning Test; RAVLT-D [40]. In this test, 15 words are verbally presented by the researcher, after which the test subject is prompted to recall as many words as possible. This is repeated five times. Delayed recall is tested after 20 min. A parallel version of the RAVLT was given at the post-training test time, T1.  
_Attention and Executive Functioning_. To assess executive functioning, the Dutch version of the Frontal Assessment Battery (FAB) was presented [41]. The FAB has six subtests: conceptualization, mental flexibility, motor programming, sensitivity to interference, inhibitory control, and environmental autonomy. Each subtest is scored from zero to three, with a score of three when the participant performs the subtest perfectly and with a score of zero when the participant fails. The total scores were recorded.  
The Dutch version of the Stroop Color Word Test was included in order to measure attention and central executive functioning [42]. This test consists of three cards. On the first card, the participant is asked to read 10 rows of the names of colors printed in black ink. On the second card, they are instructed to name the color of multiple-colored rectangles. The time was tracked during the presentation of both cards [43]. A t-score was computed for both cards. In light of low performance on the most complex card of the Stroop Test, we excluded card 3 and did not calculate an interference score.