Clock-drawing has become one of the standard cognitive screening tools used around the world. How did this particular test achieve such popularity and why is it so useful?
Originally, the clock-drawing test was cited in a leading Neurology textbook as a means of specifically assessing parietal lobe function in the brain because that is the location of visuospatial ability. However, in the 1980s our group at Sunnybrook (among others) began using the clock test and assessing its value as a broader cognitive screening tool comparable to the Mini Mental State Examination (MMSE). Its acceptability and shorter time and ease of administration has made it very popular. We use a pre-drawn circle with the instruction, “Put in the numbers so that this looks like a clock and then set the time to ’10 past 11′ ”. Drawing a clock requires multiple cognitive functions (not just visuospatial ability). It requires: visual memory of a clock; planning ability and concentration in order to place the numbers evenly around the clock circle; and abstract ability to set the time using the symbol of hands which point to the number ‘2’ to represent 10 minutes past the hour. The latter task is very sensitive to cognitive impairment as affected individuals often ‘pull’ the minute hand to point to the number ‘10’ rather than ‘2’. See figure below.
It turns out that clock-drawing correlates very well with the MMSE. It takes less time to administer and is generally very well accepted. It is as sensitive to cognitive impairment as the MMSE and picks up changes in cognition over time. Moreover, it tests frontal-executive higher-level brain functioning (abstract ability) in a way that the MMSE does not. Also, the visual impact of abnormal clocks is often an eye opener for families who may not have been aware of the full extent of cognitive dysfunction. The clock test is frequently used in combination with the MMSE as a screening battery.
Clock-drawing is of course subject to the same limitations as all screening tests including the MMSE. It is affected by level of education and should not be used alone for diagnostic purposes or for assessing the severity of cognitive impairment. However, like all good screening tests it does tap into multiple cognitive functions and can provide a ‘signal’ that calls for further inquiry or more investigations. Importantly, it also establishes a baseline for future monitoring to determine if cognitive impairment is worsening and thus increasing the likelihood of an underlying dementia.
Finally, the often asked question: “What will happen to the generation of kids who have grown up with digital clocks?” Well, for them, this test may indeed become obsolete. However, we still have many more years of the current cohort of middle-aged and elderly people for whom this test will still be useful. Warning: If you are dementing, practice does not help. So don’t bother.
Next time: A home-grown cognitive screening test from La Belle Province.