The perception of time is altered in people with lewy body dementia and may have diagnostic utility, new research shows.
Presenting his findings during the ANZAN 2019 Young Investigator Session, Dr Elie Matar, a Dementia and Movement Disorders Fellow at the Brain and Mind Centre at the University of Sydney, said cognitive fluctuations – defined as spontaneous and marked variation in cognitive function – were considered a core symptom of Dementia with Lewy Bodies (DLB).
“In the initial criteria of DLB in 1992 it was a sine qua none, meaning that you weren’t allowed to call someone a person with DLB if they didn’t have cognitive fluctuations – that’s how important [this symptom] is to this particular disorder,” he told ANZAN delegates.
“But it’s really hard to diagnose because we don’t have any particularly good objective markers to measure cognitive fluctuations,” he said.
The aim of his current study was to explore the utility of interval timing as a paradigm for understanding the psychology, and potentially, the neural mechanisms underlying cognitive fluctuations in DLB.
The research group used a simple paradigm adapted from an Oxford group that looked at time perception in three parts: time estimation, time production and time pacing.
In the time estimation task, 25 patients with probable DLB and 14 controls were given a random interval of time of either 10, 30 or 60 or 90 seconds and at the end of that interval were asked to indicate how long they thought that time was.
In the second set of experiments, participants were asked to estimate intervals of time, again measured in seconds, and say ‘Stop’ when they thought the time period had passed.
“In both of those paradigms we gave patients a number of distractors on a screen to stop them from internally counting, but to control for that we did a separate time pacing experiment where we asked them to internally count marking different seconds along the way,” Dr Matar explained.
The researchers found that time perception was fundamentally altered in patients with DLB. In the first experiment, they found that DLB patients tended to underestimate time compared to healthy controls – for instance, a 90 second period may be perceived as only 45 seconds.
In the second experiment, when the subjects were asked themselves to produce a specific period of time, the DLB subjects would tend to stop the experimenter early and ‘under-produce’ the requested interval of time.
But the research team found no difference between the groups in measures of time pacing, a finding that Dr Matar said was important because it meant that the problem was not simply due to difficulty in internal counting out time and could pinpoint other mechanisms of time perception that may be disrupted such as the accumulation of information of time passing.
Importantly, the team found a strong correlation between how poorly DLB participants performed on the time estimation paradigm (or time passing) and the severity of fluctuations, according to questionnaires completed by patients and their caregivers. By exploring different cut-offs for the task, the researchers were also able to show that a measure of time-estimation could be used to diagnose fluctuations in the clinic.
In the last set of experiments, the researchers combined the results with functional MRI (fMRI) to show that errors in time estimation in DLB subjects reflected a reduction in the ability of the brain to support dynamic ‘cross-talk’ between different regions.
“These findings demonstrate the utility of time perception as a promising new paradigm which can be used in the future with other tools such as pupillometry and task-based fMRI to investigate the mechanisms of fluctuations and which will hopefully lead to better objective markers and treatments for this important symptom,” Dr Mater concluded.