Most research points to cognitive slowing in chronic fatigue syndrome (CFS), although there have been negative reports. The present study is one of few that examines fine motor processing and the inhibition of automatic responses in a well-characterised CFS population. A total of 35 female CFS patients without current major depression and 25 female controls performed two computerised figure-copying tasks. The cognitive and fine motor processing of visual–spatial information was measured by recording reaction time (RT) and movement time (MT), respectively. The inhibition of automatic responses was assessed by introducing ‘conflicting patterns’ (i.e., patterns that were difficult to draw from the preferred left to right). A multivariate general linear model was adopted for the statistical analysis of the movement recordings. As a result, CFS was significantly associated with longer RT and MT in the pooled and in the task-specific analyses. However, there was no interaction between disease status and conflicting character of the patterns. In conclusion, these performance data on the figure-copying tasks provide confirmatory evidence for psychomotor slowing in CFS, but not for a disturbed inhibition of automatic responses. Computerised figure-copying tasks may be promising tools for use in neurobiological research and clinical trials in CFS.
Chronic fatigue syndrome (CFS) is characterised by unexplained, profound disabling and long-lasting fatigue that is of new or definite onset, which is not the result of ongoing exertion and also that it is not substantially alleviated by rest. The fatigue must be accompanied by at least four or more of the following case-defining symptoms during at least 6 months of consecutive illness: sore throat, tender cervical or axillary lymph nodes, muscle pain, multi-joint pain, post-exertional malaise, un-refreshing sleep, headaches and impaired memory or concentration (Fukuda et al., 1994). Although several aetiological factors have been identified, the underlying pathophysiology of CFS remains unclear (Prins et al., 2006).
The majority of patients with CFS complain of deficiencies in attention, concentration and memory abilities (Afari and Buchwald, 2003). Studies in CFS have described positive correlations between subjective complaints of mental fatigue and objective measurements of cognitive impairment (Capuron et al., 2006), as well as a positive correlation between cognitive impairment and functional deficits (Christodoulou et al., 1998 and Vercoulen et al., 1998). Although, in general, neuropsychological studies have produced inconsistent results, slowed processing speed, impaired working memory and poor learning of information are prominent features of cognitive dysfunction in CFS (Michiels and Cluydts, 2001). Conflicting reports may reflect sample selection bias, diagnostic heterogeneity, co-morbid psychiatric disorders, medication usage and variability among the types of neuropsychological testing batteries (Michiels and Cluydts, 2001 and Majer et al., 2008).
As to psychomotor functioning in CFS, the focus of the present study, several earlier studies reported prolonged simple or choice reaction times (RTs) (Scheffers et al., 1992, Smith et al., 1993, Marshall et al., 1996, Marshall et al., 1997, Vercoulen et al., 1998 and Majer et al., 2008), whereas others failed to find such delays (Grafman et al., 1993 and Fiedler et al., 1996). Moreover, only few studies examined fine motor processing or inhibition of automatic responses in CFS (Michiels and Cluydts, 2001). In a recent study, we compared psychomotor function between 38 well-diagnosed CFS patients, 32 major depressive disorder (MDD) patients and 38 healthy controls by means of computerised copying tasks differing in complexity (Schrijvers et al., 2009). In these tasks, figures were presented on a computer screen and the subjects were instructed to copy them into the squares of a sheet of paper that was placed on the digitiser. As a result, both patient groups demonstrated an overall fine motor slowing, with the motor component being more affected in the MDD patients than in the CFS patients, while both groups showed similar cognitive impairments. This might reflect the striatal dysfunctions reported in both conditions (Schrijvers et al., 2009).
These computerised copying tasks have earlier been shown to be suitable to determine the degree and nature of psychomotor retardation in MDD (Sabbe et al., 1996, Pier et al., 2004 and Schrijvers et al., 2008), anorexia nervosa (Pieters et al., 2003 and Pieters et al., 2006) and schizophrenia (Jogems-Kosterman et al., 2001 and Jogems-Kosterman et al., 2006). The use of this method allows a distinction to be made between the cognitive and fine motor processes that occur in response to visual stimuli. In addition, by manipulating the complexity of the figures to be copied, the processing load of the cognitive task components can be increased. Furthermore, to examine the inhibition of automatic responses, ‘conflicting patterns’ can be introduced. More precisely, our writing and drawing movements appear to be governed by certain graphic rules. These rules specify preferences with respect to starting points, stroke directions and stroke sequences (Thomassen and Tibosch, 1991). In the preferred condition, participants have to inhibit a more or less automatic response. Thus, by comparing patterns that are conflicting with these rules and ‘non-conflicting’ patterns, the inhibition of automatic responses can be quantified (Jogems-Kosterman et al., 2001).
The main objective of the current study was to further examine the pattern of psychomotor slowing in a well-characterised tertiary sample of CFS patients by means of computerised copying tasks, with a special focus on the inhibition of automatic responses. It was hypothesised that cognitive and fine motor processing of visual–spatial information would be slowed in CFS patients, as compared with healthy control individuals. In addition, we explored the effects of conflicting patterns and of increasing task complexity.
