Elucidating the neurophysiological basis of time perception

Our ability to accurately perceive time changes from one moment to the next. These variations contribute to moment-to-moment fluctuations in our experience of the world and other psychological functions such as coordinating our movements in response to environmental cues. Variations in our perception of time are thought to be caused in part by fluctuations in a specific brain chemical, dopamine. Dopamine is believed to activate brain regions involved in matching time intervals against other intervals we hold in memory and thereby affecting how we perceive the passage of time. When and how dopamine influences our experience of time is poorly understood because until very recently it was impossible to measure dopamine in the human brain over short timescales. A newly-developed method, fast-scan cyclic voltammetry (FSCV), allows us to accurately measure dopamine in humans and thus offers an excellent opportunity to study how dopamine contributes to variations in human time perception for the first time. Another method, electroencephalography (EEG), allows us to record a particular brain rhythm (beta oscillations) that is closely associated with dopamine and can thereby provide a complementary way to study the role dopamine plays in affecting different phases of time perception.

The proposed research aims to use FSCV and EEG to investigate whether moment-to-moment variations in time perception can be predicted from participants' brain states. FSCV will be used to measure dopamine concentrations in striatum, a brain region previously implicated in time perception, in Parkinson's patients whilst they complete time perception tasks. This will allow us to determine whether dopamine concentrations can be used to predict how participants perceive time. Further analyses will investigate whether dopamine plays a similar role in time perception when we're storing an interval in memory as when we're trying to remember an interval and whether dopamine plays a similar role in both time perception and other cognitive functions such as attention and working memory. In a second, complementary set of studies, an advanced analysis technique, multivariate pattern analysis, will be applied to EEG data in healthy adults whilst they complete the same time perception tasks. This method will allow us to determine approximately when in time participants' experiences of time can be predicted and the role of specific brain rhythms. This approach will also help to clarify whether similar brain mechanisms support different phases of time perception and both time perception and other cognitive functions.

This project has the potential to significantly advance current understanding of how fluctuations in brain states influence our subjective experience of time. This research will help to update contemporary theories of timing including when and how brain states shape our perception of time, how these states contribute to different phases of time perception, and how time perception relates to other basic psychological functions. Our perception of time influences how we perform a variety of actions such as coordinating our movements and predicting the trajectory of a ball so that we are able to catch it. Superior understanding of the brain mechanisms that contribute to variability in time perception may thus help to understand the sources of variability in human performance more generally. Individuals with different disorders such as Parkinson's disease and schizophrenia experience pronounced alterations in their perception. These time distortions are typically characterized by increased variability in the perception of time. By helping to strengthen current understanding of how variability in brain states contributes to fluctuations in our time perception, this project may also help to provide a methodological and theoretical framework for studying these distortions in a more refined manner including how they relate to other clinical symptoms.

The ability to accurately perceive time represents a fundamental but poorly understood psychological function that impacts diverse facets of human cognition from conscious experience to motor control. Previous research suggests that variations in interval timing are driven by transient fluctuations in striatal dopamine but until recently there was no method for accurately measuring subsecond dopamine concentrations in the human brain. In turn, the role of dopamine and beta (15-30Hz) oscillations, which are generated in basal ganglia and closely associated with dopamine, in the formation of temporal representations is poorly understood. This project will harness recent advances in dopamine measurement in humans (fast-scan cyclic voltammetry [FSCV]) and a state-of-the-art analytic approach for decoding mental representations from electroencephalography (EEG) data (multivariate pattern analysis [MVPA]) to determine the role of striatal dopamine concentrations and beta oscillations in shaping variations in human time perception. FSCV will be used to measure subsecond striatal dopamine concentrations in Parkinson's patients whilst they complete temporal discrimination tasks. These data will help to clarify whether fluctuations in striatal dopamine are associated with variations in perceived duration and the time course of these effects. Independently, MVPA will be applied to EEG data recorded whilst healthy adults complete the same tasks. These data will identify the time course of the formation of temporal representations and whether this is specific to dopamine-relevant (beta) oscillations. Further analyses will contrast the temporal estimates of representation formation across methods in order to determine when striatal dopamine impacts interval timing. This project will reveal new insights into the roles of striatal dopamine and beta oscillations in the formation of temporal representations with implications for the sources of variability in human time perception.

The proposed research aims to use newly-developed methods and techniques to provide novel insights regarding how the human brain perceives time. This project will be the first of its kind to harness these approaches in order to elucidate the neural mechanisms supporting this critical but poorly understood cognitive function. In turn, this research promises to have a considerable impact on non-academics including clinicians, engineers, and the broader public.

A major focus of the proposed research is clarifying the role of the neurochemical dopamine in the perception of time and in particular how it may underlie variability in human time perception. Numerous psychological and neurological disorders are characterized by aberrant dopamine and distortions in time perception including Parkinson's disease, Huntington's disease, and schizophrenia. In many of these conditions, the primary feature of distorted timing is increased variability in time perception and this variability is believed to play a potentially significant role in these conditions. For these reasons, potential beneficiaries of this research include clinicians involved in the treatment of such conditions as well as the individuals who are afflicted by them. By clarifying how aberrant dopamine levels contribute to variability in time perception, this project may help to inform pharmacological treatments for these conditions.

The proposed research aims to apply a state-of-the-art method for precisely measuring dopamine in patients. Although validated and robust, this method has only recently been developed and is likely to undergo further advances in terms of its use and efficacy. Biomedical engineers and those working in biomedical imaging will benefit from the proposed research, which aims to further validate this approach and use it to examine complex neural processes. At the end of the project, all data will become publicly available and can be used by engineers to further explore pertinent questions regarding the efficacy of this method, its constraints, and its potential in clinical contexts. This research will provide an impetus for further development of these methods by engineers working in medical contexts. Long-term, these methods might be used for directly monitoring and altering dopamine concentrations in order to more precisely control time perception, with implications for other psychological functions such as timing-based motor control. Most of the previous research on the questions addressed in this project has been conducted with non-human animals. By utilizing a novel set of methods and techniques for studying human time perception, the proposed research may similarly contribute to the reduction in the use of non-human animals in the study of time perception.

Time is also a perennially fascinating phenomenon that captures the public imagination and interest and has a huge influence on popular culture. I will aim to communicate the scientific advances made by this project to the public through multiple outlets in order to increase understanding of time perception and its importance and I hope that this will further help to increase the public's engagement with scientific research as well as neuroscience and psychology more generally.