The Role of Beta Oscillation in Mental Time Travel
Condition: Healthy Population
Study type: Observational

Summary: 
      The project aims to study the neural basis of Mental Time Travel (MTT), i.e. the ability to
      travel back and forth in time. It has been proposed that the self-projection in time is
      similar to the self-projection in space, emphasizing the role of spatial navigation in MTT.
      Indeed, the posterior parietal cortex, a key region for visual imagery in space-related
      tasks, and the temporo-parietal junction, a key region for mental projection, are both
      recruited by self-projection in time and space. However, the specific neural computation of
      the two processes remains unclear. One way to address this is by investigating the brain
      oscillations that may modulate MTT. One plausible candidate for MTT processing are beta
      oscillations because of their role in the production and perception of short temporal
      intervals, as opposed to alpha oscillations which correlate with illusory changes in self
      location in space. Thus, the present project investigates the hypothesis that MTT may rely on
      posterior parietal cortex's beta oscillations to self-project in time. Moreover, cause
      previous studies showed a different performance in time processing between young and elderly
      health population, we want to investigate also if there is a difference between these two
      populations in the capacity to travel mentally in time.
    

Detailed description: 
      A characteristic of human conscious experience is the ability to mentally project oneself to
      a new time location, either in the past or in the future, i.e. the so-called Mental Time
      Travel (MTT). The aim of the present project is to study the neural basis of MTT.

      It has been proposed that the self-projection in time is similar to the self-projection in
      space, emphasizing the role of spatial navigation in MTT. Indeed, the posterior parietal
      cortex, a key region for visual imagery in space-related tasks, and the temporo-parietal
      junction, a key region for mental projection, are both recruited by self-projection in time
      and space. However, the specific neural computation of the two processes remains unclear. One
      way to address this is by investigating the brain oscillations that may modulate MTT. One
      plausible candidate for MTT processing are beta oscillations because of their role in the
      production and perception of short temporal intervals, as opposed to alpha oscillations which
      correlate with illusory changes in self location in space. Thus, we hypothesize that the MTT
      may rely on posterior parietal cortex's beta oscillations to self-project in time. Moreover,
      because previous studies showed a different performance in time processing between young and
      elderly health population, we want to investigate also if there is a differences between
      these two populations in the MTT.

      To assess the MTT we developed a new task in which participants see stimulus faces of
      different ages, one at a time. Each face is presented with a short phrase describing a
      particular life event, commonly happening in middle age. Participants perform a 2-alternative
      forced choice: in the 'Past Projection', they indicate if it is likely or unlikely that the
      stimulus person has lived the life event 10 years ago; in the 'Future projection' that the
      stimulus person will live the event 10 years in the future. We use transcranial alternating
      current stimulation (tACS) to test within subjects the role of target (Beta) and control
      oscillations (Alpha), in addition to a control non-stimulation condition (Sham). To rule out
      that tACS may simply affect age perception, participants are also asked to report the age of
      each stimulus face (Age Estimation task). Moreover, to investigate if there is any
      correlation between the MTT and the perception of short temporal interval, participants
      perform a time reproduction task before the brain stimulation and the MTT task. In the Time
      Reproduction task, a blue square is presented with a variable duration (encoding phase).
      Immediately after the encoding phase, a red square of the same size and position is
      presented. Subjects press a response button when they considered that the same of the
      previously studied time interval has elapsed.

      A pilot study from 11 participants shows that beta-tACS corresponds to a shift in the
      psychometric curve towards a younger age in the 'Past condition', and towards an older age in
      the 'Future condition'. Thus, participants indicated a younger face as more likely to have
      lived an event 10 years ago and an older face as more likely to live an event 10 years in the
      future. This suggests that beta-tACS leads to an under-estimation of time relative to sham
      and alpha-tACS. Crucially, there were no significant differences in estimating the veridical
      ages of the stimulus faces. Thus, beta oscillation may modulate self-projection in time,
      since these data are consistent with an under-estimation of time.

      If confirmed, results will allow us to specify that self-projection in time relies on the
      posterior parietal regions and beta oscillations. Moreover, if supported by our future
      experiments involving space processing, this result may also shed a new light on the
      distinction between self-projection in space, which is known to rely on alpha, and
      self-projection in time that relies on beta. Overall, these data may point to the fact that
      beta oscillations are critical for processing long durations, in addition to their well-known
      role in supporting short durations. This may be because beta oscillation may serve as a
      memory standard to which different durations are compared.
    

Intervention name(s): Beta tACS; Alfa tACS; Sham
Intervention type(s): Behavioral; Behavioral; Behavioral
Intervention description(s): participants perform the Mental Time Travel task (duration 20 minutes), while tACS stimulation is delivered at Beta frequencies (22 Hz); participants perform the Mental Time Travel task (duration 20 minutes), while tACS stimulation is delivered at Alfa frequencies (10 Hz); participants perform the Mental Time Travel task (duration 20 minutes), while Sham tACS stimulation is delivered
Observational model: Other
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        Two groups of healthy partcipants. Age between 20-30 for the first group and age between
        60-80 for the second group
      
Keywords: Time Perception; Mental Time Travel; tACS; Brain Stimulation