Among other medico-legal concepts,  the ‘lucid interval’ is a long held concept widely accepted in case law as a possible means of countering a challenge to testamentary and related capacities.  In parallel, the clinical phenomenon of cognitive fluctuation has been considered a common element of several neurodegenerative disorders (dementias) including Alzheimer Disease, but especially prevalent in Vascular Dementia and Dementia with Lewy Bodies. In the spirit of the philosopher Karl Popper, one should always be skeptical about ‘established’ facts or concepts and constantly try to disprove them if possible. With that spirit in mind (together with Ian Hull, who provided the legal background and Psychiatry colleagues at Sunnybrook), we reviewed the objective evidence for cognitive fluctuations in dementia and the implications for the validity of the legal notion of the ‘lucid interval’ cited in recent case law.

The literature on cognitive fluctuations in dementia shows that such fluctuations largely affect attention and alertness rather than memory or higher level executive functions (eg. – planning and judgment), which are essential components of testamentary capacity. Moreover, these fluctuations are quite small in magnitude and very short in duration. These findings cast doubt on the validity of the ‘lucid interval’ and invite a critical re-thinking of this legal concept as applied to Will challenges involving testators suffering from dementia.

Another small victory for the myth busting ‘Team Iconoclastia’!