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).
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)..
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).
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.