Subsecond timing relies on dynamic excitability of local cortical circuits

We know that the passage of time at multiple time scales can influence neural activity. But what brain mechanisms are responsible for the encoding of time itself? Is there a specialised mechanism or module that measures the elapsed time and informs other brain areas or neuronal populations about the current position on the time axis? Or is time encoded in a distributed way, with – in principle – any part of the cortex involved in processing some information also intrinsically containing information about time?

In a recent article in Neuron, Goel & Buonomano argue for the latter, showing that neurons in a cortical slice in vitro – by definition isolated from any external circuit dedicated to measuring time – can be trained to represent time elapsed (at a subsecond scale) between an electric stimulus and optogenetic activation. The experiments were conducted in slices of cortical tissue implanted with electrodes used to deliver electric shocks which evoked neural activity. The slices were also transfected with a virus expressing channelrhodopsin, thanks to which cells were activated by optical stimulation (blue light shone above the tissue). First, the slices were subject to prolonged “training”, in which optical stimulation was delivered after the electric shock and a brief, constant time interval (100, 250, or 500 ms). After training, slices were “tested” – the electric shocks were delivered without being followed by the light. However, most superficial pyramidal cells in the slices spiked not only in response to shock, but also later, several hundreds of milliseconds after the initial peak. Crucially, the interval between the two waves of activity depended on previous training: the second wave of activity appeared around 100 ms if the slices had been trained to receive light 100 ms after the electric shock, and progressively later if the training had involved longer intervals.

While this finding shows that a generic part of the cortex can be trained to represent temporal regularities in its activity – without receiving inputs from another area serving as an external “clock” – these results might be explained either by single cells adapting their time constants in an experience-dependent way, or by the whole network of neurons encoding time in a dynamically evolving pattern of its activity. To disambiguate between these two possibilities, another experiment was conducted. This time the slices were implanted with two electrodes. In the training phase, one electrode was paired with an optical stimulus as before, delivered 100 ms after the shock. The other electrode was used to stimulate the cortical slice without an associated light stimulus (“unpaired” pathway). In the test phase, after a spike evoked by the electric shock, many of the neurons that had been classified as lying on either the paired or the unpaired pathway spiked again later. Crucially, this second wave of activity in neurons on the paired pathway was more pronounced and occurred markedly closer to the 100 ms mark than the secondary activation of neurons on the unpaired pathway. These results can be interpreted as pathway-sensitive learning, where the paired pathway is associated with more polysynaptic activity, and the timing of this activity – while not always coinciding with the expected interval (see below) – is closer to the expected interval.

To better understand the time-specific secondary response of the network in a more dynamic and mechanistic way, the authors performed two further experiments. First, they interleaved the training phase with test phases after 1 and 2 hours of pairing electric shocks with light. The results of this experiment showed that after 1 hour, the activity along the paired pathway increased (compared to the unpaired pathway) but not in a time-specific way. However, after 2 hours of training, the secondary peak of activity also depended on the trained interval, with the neurons trained using the 100 ms interval firing earlier than those trained at 500 ms.

Interestingly, the authors also observed that the probability of a light-evoked spike changed over the course of training. In cells which typically responded to light alone, just after pairing the light stimulus with an electric shock, the probability of a spike evoked by the light decreased dramatically to only 25%, and recovered during training to around 70%. This suggests that, during the initial phase of the training, the electric shock induces strong inhibition in the network which prevents the optical stimulus from activating the light-sensitive neurons. Later, this inhibition might decrease, leading to more neurons firing in response to light. The authors tested this hypothesis by separately measuring the excitatory and inhibitory currents evoked by the electric shock. It turned out that the ratio of excitation and inhibition differed between the paired and unpaired pathways only around the trained time interval, but not earlier or later. This result demonstrates that the network might have learned to dynamically shift the balance of excitation and inhibition in a training-dependent way.

Across the experiments, the exact timing of the secondary activity did not always coincide with the trained interval. For example, looking at slices trained at the 100 ms interval, experiment 1 – with only the paired pathway – resulted in secondary activity after approximately 100 ms, but further experiments – with both the paired and unpaired pathways – showed secondary activity peaking closer to 200 ms or even 250 ms. While the authors do not address these discrepancies, one could argue that the paired and unpaired pathway will strongly overlap in a densely interconnected slice, with neurons being indirectly depolarised by inputs from both pathways.

The time-specific balancing of excitation and inhibition suggests that, when looking at dynamic modulations of neural excitability, subtle measures of network activity might be a better choice than overall firing rates. Similar arguments have recently been raised in cognitive neuroscience, where non-invasive measurements often show dynamic changes of neural states without accompanying persistent activity.

It is important to note that the experiments were confined to a subsecond time scale. Different mechanisms might be at play at longer time scales. Crucially, temporal encoding in the order of seconds might more likely rely on cortico-hippocampal loops rather than local cortical networks.

Ryszard Auksztulewicz, Oxford Centre for Human Brain Activity

Source article: Goel A, Buonomano D (2016) Temporal interval learning in cortical cultures is encoded in intrinsic network dynamics. Neuron 91(2):320-327. doi: http://dx.doi.org/10.1016/j.neuron.2016.05.042

Spontaneous Eye Blinks may explain moment to moment changes in time perception

Everyday we encounter so many events which alters our sense of time. For example, waiting for someone over telephone or experiencing pain seems longer in time then actual, whereas spending time with loved ones or playing video games seems shorter. Many factors like attention, arousal, emotion, etc are known to influence subjective time. But a recent study by Dr. Devin Terhune (Department of Psychology, Goldsmiths, University of London) and his collaborators [Jake Sullivan, Department of Experimental Psychology, University of Oxford & Jaana Simola, Neuroscience Center, University of Helsinki] published in Current Biology, for the first time showed that the moment to moment time perception changes can also occur due to spontaneous fluctuations in the striatal dopamine.

The study by Dr. Devin Terhune, very cleverly utilized the findings from two line of work, first are those pharmacological studies which links time perception and level of dopamine. And second are those studies which links the level of striatal dopamine and rate of spontaneous eye blinks. Based on these studies they hypothesized that, since spontaneous eye blink are indicator of rise in striatal dopamine, then the time perception for the trials after the blink should be different from those trials which were not preceded by an eye blink. So they had two conditions, post-blink trials and post-no-blink trials. They used temporal bisection task wherein participants were first trained for two standard durations (for sub-second range, short standard-300ms and long standard-700ms) before the main experiment and were suppose to judge whether they perceived the duration of the visual test stimuli (randomly 300ms, 367ms, 433ms, 500ms, 567ms, 633ms, and 700ms) as closer to short or long standard duration. While participants performed the temporal bisection task their eye moments and blinks were recorded using an eye tracker. Monitoring the eye blinks enabled them to categorize each trial based on whether the participants blinked or not in the previous trial. They found that participants perceived the duration of the post-blink trials as longer compared to post-no-blink trials, as indicated by the leftward shift of psychometric function in the post-blink condition compared to post-no-blink condition.

These results were successfully replicated even for auditory stimuli and also for supra second visual stimuli (short standard-1400ms, long standard-2600ms; duration of test stimuli-1400ms, 1600ms, 1800ms, 2000ms, 2200ms, 2400ms, and 2600ms). Moreover, in all the three experiments there was no difference in the temporal precision, indicated by no difference in Weber fraction (WF) and difference limen (DL) between the two critical conditions. WF and DL are measures of temporal sensitivity where smaller values means better sensitivity.

The key contribution of this study is that along with demonstrating the moment-to-moment intra-individual changes in time perception, it also provides a new, simple and innovative design for studying intra-individual changes in time perception associated with endogenous fluctuations in striatal dopamine. It also has implications in understanding the temporal perception in clinical disorders associated with dopamine like Parkinson’s.

Source: Terhune, D. B., Sullivan, J. G., & Simola, J. M. (2016). Time dilates after spontaneous blinking. Current Biology, 26(11), R459-R460. DOI: http://dx.doi.org/10.1016/j.cub.2016.04.010

—Mukesh Makwana, mukesh@cbcs.ac.in
Doctoral student,
Centre of Behavioural and Cognitive Sciences,
University of Allahabad, India.

PhD position on the experience of time in Philosophy, University of Tartu (Estonia)

The University of Tartu announced an open call for two PhD positions in Department of Philosophy, one of which is on ‘Experience of time’ (supervisor Bruno Mölder):

Time seems to enter our experiences in various ways: the events we experience have temporal properties, e.g., when we experience things changing or moving; experiences themselves stand in temporal relations to each other and so on. This leads to several philosophical issues concerning the experience of time:
–   How is the time in experience related to objective time?
–   How is the time in experience related to the temporal properties of brain processes that underpin experience?
–   Does consciousness have some kind of temporal structure?
The prospective candidates must show potential to make a significant contribution to philosophical debates related to such themes. Depending on the nature of the project, background in psychology or metaphysics is advisable.

Admitted PhD students will be enrolled in the Philosophy PhD programme. The nominal study period is 2017-2021, starting from the beginning of February 2017.

Research and studies will be funded by the programme DoRa Plus (European Regional Development Fund). Full time PhD student will be receiving a monthly grant of 422 EUR during the nominal period of studies (4 years) and annual travel allowance (return travel between home and Tartu).

Application deadline: December 1, 2016.

All particulars about the research topics, eligibility conditions, application materials and assessment criteria available here: https://www.ut.ee/en/2-phd-positions-programme-philosophy

Call for Participation: 16th Rhythm Production and Perception Workshop 2017

Call for Participation
16th Rhythm Production and Perception Workshop (RPPW) 2017
3rd-5th July 2017
Millennium Point, Curzon Street, Birmingham, UK, B4 7XG.
http://dmtlab.bcu.ac.uk/rppw2017/

Confirmed Keynote Speakers
Douglas Eck – Google, Inc.
Peter Keller – MARCS Institute, Western Sydney University

About
The 16th RPPW will be held at the Digital Media Technology Lab in Birmingham City University’s Millennium Point Campus in Birmingham, UK from the 3rd to the 5th of July 2017. RPPW is an international biannual event that brings researchers from a range of disciplines together to engage in discussions about the scientific study of rhythm. Rhythm is at the core of a wide range of human tasks, from speaking and dancing, to walking and synchronising with others. The workshop is traditionally centred around psychology and neuroscience, however this year we are additionally encouraging participation from the Music Information Retrieval Community to encourage cross-pollination and interdisciplinary collaboration. The workshop will host oral presentations, posters and tutorials with satellite activities.

Call for submissions
Presenters are asked to submit abstracts of up to 500 words in length plus references for poster and oral presentation. Abstracts will be peer reviewed by the paper committee and successful applications will be published online. The submission portal (http://dmtlab.bcu.ac.uk/rppw2017/authors/) will open on the 1st of November and will close on the 15th of January 2017. Short proposals for tutorials and workshops should be sent by email to ryan.stables@bcu.ac.uk.

Topics
Potential topics include (but are not limited to):

  • Rhythm and synchronisation
  • Synchrony and order perception
  • Multisensory temporal processing
  • Acquisition of time knowledge and temporal concepts
  • Timing and memory, attention, emotion and metacognition
  • Beat tracking and onset detection
  • Music Structure analysis
  • Expressive timing and performance modelling
  • Ensemble or group performance
  • Entrainment
  • Rhythm in neurorehabilitation

Important Dates
1st November 2016: Submission system opens
15th January 2017Deadline for abstract submissions
30th January 2017: Notification of acceptance
2nd July 2017: Pre-conference reception
3rd-5th July 2017: Conference

Bursaries
We are planning on offering student bursaries, more information in due course.

Sponsorship
If you would be interested in sponsoring the event, please contact ryan.stables@bcu.ac.uk.

Timing Research Forum Newsletter – October 2016

Dear all,

We are pleased to share the second newsletter of the Timing Research Forum (TRF).

 

  1. TRF UPDATE

We are proud to claim a membership that is now ~400 members strong! The website is very popular with ~12000 total hits.

 

We have now expanded to 132 followers on Twitter and 135 on Facebook. Both social media pages are being actively used by the members to share timing related papers, publications, calls for conferences and symposia, request for experimental participants, and other related updates. Join us and share your work and news!

  1. TRF CONFERENCE

We are pleased to confirm the dates for the first TRF conference that will be held from October 23-25, 2017 at the University of Strasbourg, France. Anne Giersch and Jenny Coull are the hosts and have already shown excellent initiative and progress with the organizational aspects of the conference. We look forward to working with them to finalize the format of the conference program. We will disseminate updates and the conference website as soon as we have them, till then please save the dates for the 1st TRF conference.

III. TRF ASSOCIATE MEMBERS

Our call for TRF Associate Members in the previous newsletter received a tremendous response and we are happy to announce their names below.

TRF BLOGGERS

TRF Bloggers will review at least one timing paper of their choice and blog about it on the TRF website. Each blog post will be open for comments and further discussions so we look forward to your contribution and hope to have lively and thoughtful discussions!

Molly J. Henry

Postdoctoral Fellow

Brain and Mind Institute, The University of Western Ontario, Canada

Bharath Chandra Talluri

PhD Student

Department of Neurophysiology and Pathophysiology, University Medical Centre, Hamburg-Eppendorf, Germany

Mukesh Makwana

PhD Student

Centre of Behavioural and Cognitive Sciences, University of Allahabad, India

Ryszard Auksztulewicz

Postdoctoral Fellow

Oxford Centre for Human Brain Activity, University of Oxford, UK

Bronson Harry

Postdoctoral Fellow

MARCS Institute for Brain, Behaviour and Development, Australia

 

TRF SOCIAL MEDIA & NEWS MANAGER

The candidate will be responsible for sharing timing related news including:

  1. a) publication of new papers, journal special issues, and books
  2. b) timing events, conferences, workshops etc.
  3. c) grants and funding opportunities
  4. d) job openings at the doctoral, postdoctoral, and faculty level
  5. e) encouraging TRF members and attendees at timing conferences to tweet

 

Bowen Fung

PhD Student

Decision Neuroscience Laboratory, University of Melbourne, Australia

TRF MAILING LIST MODERATOR

The mailing list moderator will ensure the approval of member posts and will keep the TRF mailing list clean from SPAM or unwanted emails.

Nadine Schlichting

PhD Student

Time Perception Laboratory, University of Groningen, Netherlands

  1. TIMING MEETINGS

Please visit – http://timingforum.org/timing-meetings/ for an updated list of timing meetings.

  1. TRF’s RESOURCES AND YOUR CONTRIBUTION

TRF aims to host timing related resources, so that TRF‘s website will be the one stop for everything related to timing. Currently, the TRF website has these resources: all members’ publications, timing related special issues, and books on timing, a list of meetings focused on timing, a list of timing related societies/groups, as well as code and mentoring resources.

 

We ask all of you to contribute to these resources. Please send us (by emailing us at trf@timingforum.org) any omissions that we might have or any new information that should be added.

 

TRF is based on the idea of sharing information freely between its’ members so as to advance timing research and group collaborations. Thus, we encourage all of you to share with us any of the above resources that you might have and/or suggest new resources that we should add and circulate within the community.

  1. FEEDBACK

We thank all of you for supporting this community and hope that you will continue to do so in the future. As we continuously emphasize, TRF is meant to be open to all timing researchers with the aim of sharing

ideas and advancing the current state of the art. Thus, we are open to any suggestions or ideas that will help TRF grow and advance. We have already established many ways (website, mailing list, resources etc.) to

discuss the current state and the future of TRF and these tools will become more active in the coming months. We are looking forward to all of your feedback!

With best wishes,

 

Sundeep Teki                        &                  Argiro Vatakis

University of Oxford                                   Cognitive Systems Research Institute

sundeepteki.org                                         argirovatakis.com