Rück makes reference to a series of studies reporting personality change following anterior capsulotomy, including his recent review of 26 patients undergoing thermal capsulotomy for anxiety (Reference Rück, Andreewitch and FlycktRück et al, 2003). He raises interesting questions about the prevalence of personality change following certain (if not all) neurosurgical procedures for mental disorder, and such questions remain, we believe, essentially unaddressed by previous research. Rück's rate of apparent personality change following anterior capsulotomy is comparatively high at approximately 30% of patients. This rate is higher than those rates reported in earlier literature, which suggest rates of up to 10% for stereotactic subcaudate tractotomy (Reference Strom-Olsen and CarlisleStröm-Olsen & Carlisle, 1971; Reference Goktepe, Young and BridgesGoktepe et al, 1975) and 2% for stereotactic cingulotomy (Reference Dougherty, Baer and CosgroveDougherty et al, 2002). However, 24% of patients undergoing limbic leucotomy had transient apathy which resolved fully (Reference Montoya, Weiss and PriceMontoya et al, 2002).

In addition to the lack of uniformity of measurement across studies, another key difference may lie in the fact that many of the larger studies included patients with a variety of diagnoses, including depressive disorder, obsessive–compulsive disorder (OCD) and anxiety disorder. In fact, non-OCD anxiety disorders made up a small percentage of most of the studies cited above, whereas Rück's study sample comprised entirely patients diagnosed with non-OCD anxiety disorder.

The lesions of anterior capsulotomy disrupt the continuity of the frontostriatal–pallidal–thalamic circuits which are believed to be dysfunctional in OCD (Reference Modell, Mountz and CurtisModell et al, 1989). Important connections between the orbitofrontal cortex, anterior cingulate regions and the thalamus also lie in the anterior part of the internal capsule and are thought to play an important role in the pathogenesis of major depressive disorder (Reference Tekin and CummingsTekin & Cummings, 2002).

Most psychiatrists, neurologists and neurosurgeons would probably predict high rates of serious psychopathology – including personality changes – if such lesions were made within ‘healthy brains’. If the existing literature can be considered reliable, including the report of Rück and colleagues, it is quite remarkable that the reported rates of significant frontal psychopathology are so infrequent. Hence, three possibilities (at least) must be considered:

1. (a) that neuropsychological and personality screening for frontal impairment has been grossly inadequate in almost all studies;

2. (b) that the deleterious effects of frontal surgery on patients with chronic intractable affective disorders may be minimised because the target brain structures are already dysfunctional, perhaps with important frontal functions being undertaken by non-frontal structures (such plasticity of mammalian brain function is plausible, see e.g. Reference Kolb and GibbKolb & Gibb, 1993);

3. (c) different forms of psychiatric disorder may be associated with different risks of adverse consequences following NMD; for example, thermal capsulotomy for non-OCD anxiety disorders may present a higher risk of frontal psychopathology than capsulotomy for OCD or depression.

In reality, the true picture may represent a combination of influences from these three factors. What is clear is that all NMD must be accompanied by detailed prospective audit with comprehensive evaluation of ‘frontal’ neuropsychology and personality functioning.