Thienel, R, Bender, S., Oades, R. D., Dittmann-Balcar, A., & Schall, U. , (2001).
Auditory information processing and planning of responses in the Tower-of-London test over a course of therapy in patients with obsessive compulsive disorder (OCD). Auditorische Informationsverarbeitung und Planungsverhalten im Tower of London-Test im Therapieverlauf zwangserkrankter Patienten. Nervenheilkunde, 20, (suppl 3), 133.
(German abstract, English poster)

There is some evidence for prefrontal brain-related deficits of executive function in patients with obsessive compulsive disorder (OCD).
Methods:
Auditory sensory gating, the Tower of London task (TOL) and the Yale Brown obsessive-compulsive rated symptoms were studied in 11 patients diagnosed with OCD and contrasted with 27 healthy control subjects. Patients were tested at treatment onset and after 6-12 weeks. Controls were studied in a similar time frame. The gating measure on an auditory Go/no-go discrimination was the difference ERP frontal P3 waveform (nontarget-minus-target) in a 100 ms prepulse condition. (i.e. prepulse induced non-taget positivity: PINTP, see Bender et al. 1999). The TOL is a test of visuospatial working memory with measures of the time taken to plan the moves, then to execute the task (a series of 15 problems of increasing difficulty, involviung 2-7 moves)..
Results:
1/ Clinical symptoms improved in the course of treatment - obsession scores halved and compulsions were reduced by a third.
2/ At onset, the patients showed a reduced PINTP amplitude and prolonged TOL planning times (vs. controls).
3/ In the course of treatment there was significant increase of PINTP and reduction of the time necessary for planning the execution of the TOL task.
4/ However, unlike the patients with schizophrenia (Oades et al. 1999a, 1999b) there were no associations between the measures (clinical ratings, gating and TOL perfomance).
Conclusion:
The improvements of measures of executive function and gating indicate a likely improvement of frontal lobe function, but there was surprisingly no association with the reduction of clinical symptoms.