Brain: how do we experience time?

How does our brain appre­hend time? We put the ques­tion to Vir­ginie van Wassen­hove, research dir­ect­or at the CEA and head of the Inserm team, whose CHRONOLOGY pro­ject has just been awar­ded a Syn­ergy grant from the European Research Coun­cil, worth up to €10 mil­lion over 6 years.

Vir­ginie van Wassen­hove. It’s an ambigu­ous rela­tion­ship! Psy­cho­lo­gic­al time does not coin­cide with phys­ic­al time, it isn’t com­pletely dis­con­nec­ted from it either. Let’s take a few examples: we’re per­fectly cap­able of estim­at­ing time very accur­ately when we have to cross a ped­es­tri­an cross­ing or play ping-pong, but we lose pre­ci­sion if the time to be eval­u­ated gets longer, or if we’re dis­trac­ted by oth­er stimuli.

Sim­il­arly, an hour spent in a dent­ist’s wait­ing room will seem much longer than an hour spent on a first date. Let’s go a step fur­ther. If we try to recall these two epis­odes years later, our tem­por­al exper­i­ence will be reversed: the wait at the dent­ist will seem much short­er than it actu­ally was, and the romantic date much longer, because it was rich in emo­tions and micro-events to which we paid attention.

The ques­tion of psy­cho­lo­gic­al time is there­fore com­plex, but fun­da­ment­al, because it is on the basis of this men­tal rep­res­ent­a­tion that we pro­ject ourselves into the future and the past, devel­op our think­ing, make short- and long-term decisions, in short, com­mit ourselves to life.

My interest in time dates back to the mid-2000s, dur­ing my post-doc­tor­al work when I was work­ing on the pro­cessing of multi­s­ens­ory inform­a­tion by the brain. The sens­ory stim­uli asso­ci­ated with the same event are con­veyed in dif­fer­ent forms of energy (vibrat­ing molecules for sound, photons for vis­ion, etc.) and do not reach the brain at exactly the same time. 

The notion of sim­ul­tan­eous­ness is there­fore entirely recon­struc­ted by the brain. But determ­in­ing sim­ul­tan­eous­ness is cent­ral, because it con­di­tions our per­cep­tion: it is in fact pre­cisely the moment when con­scious­ness appears. So I began to take an interest in how neur­ons code tem­por­al­ity, or in oth­er words, the men­tal rep­res­ent­a­tion of time. I spent a sum­mer read­ing almost a cen­tury of lit­er­at­ure on the sub­ject, without find­ing any sat­is­fact­ory answers. A new field of study was open­ing up for me.

Very few neur­os­cient­ists asked the ques­tion of psy­cho­lo­gic­al time in terms of neur­on­al cod­ing and men­tal rep­res­ent­a­tion. The lit­er­at­ure seemed to be con­tent with the mod­el of an intern­al clock syn­chron­ised with extern­al rhythms, which would beat time and record the beats to count dur­a­tions. This concept emerged after the dis­cov­ery of brain rhythms, and in par­tic­u­lar the alpha rhythm, a brain wave with a peri­od of 100 ms that can be observed in all con­scious indi­vidu­als. Because this rhythm is a pri­ori very reg­u­lar, the work­ing hypo­thes­is was that it beat the tempo of the intern­al clock. But the rhythmi­city of cer­tain neur­on­al activ­it­ies is not enough to explain how the brain rep­res­ents time.  Com­ing from the field of sens­ory per­cep­tion, this seemed obvi­ous to me: tak­ing the ana­logy of the men­tal pro­cessing of col­our, it would be like ima­gin­ing that to trans­mit red inform­a­tion, the neur­ons them­selves would have to turn red.

The intern­al clock mod­el is there­fore use­ful, because it pre­dicts some of our beha­viour, but it did­n’t seem to me to be real­ist­ic from a neuro­bi­o­lo­gic­al point of view. Recent stud­ies using func­tion­al neuroima­ging at high tem­por­al res­ol­u­tion (such as elec­tro­en­ceph­al­o­gram [EGG] and mag­ne­to­en­ceph­al­o­graphy [MEG]), includ­ing those car­ried out by my team, have sub­sequently shown that this is not the case.

We were able to estab­lish¹ that the alpha rhythm is not con­stant, and this char­ac­ter­ist­ic is incom­pat­ible with the very idea of a clock. So, there are some nuances to be made: yes, brain rhythms are cer­tainly involved in tem­por­al pro­cessing, but the story is more com­plic­ated than the intern­al clock mod­el sug­gests. And that’s just as well… because if our con­cep­tion of time were gov­erned solely by bio­lo­gic­al clocks set to extern­al rhythms, we would have to con­clude that we are in a con­stant state of atten­tion­al cap­ture and we would not be able to explain the sta­bil­ity of our think­ing. Yet sta­bil­ity of thought is abso­lutely neces­sary for the emer­gence of con­scious­ness. Our brain must there­fore have a stable sys­tem for rep­res­ent­ing time, a time ref­er­ence sys­tem that is largely immune to extern­al tem­por­al inform­a­tion. This is obvi­ous when we con­sider time travel.

The abil­ity we have to ima­gine ourselves far into the past or pro­ject ourselves into the future. This time travel, which could be unique to human beings, requires a high degree of abstrac­tion: we have to be able to estab­lish a map of time in which we can move (men­tally), while pre­serving the tem­por­al rela­tion­ships between events. The intern­al clock alone can­not explain this ability.

In 2014, John O’Keefe, May-Britt Moser and Edvard I. Moser were awar­ded the Nobel Prize in Medi­cine for their dec­ades-long work in demon­strat­ing the exist­ence of a ‘GPS’ with­in the brain. Their work showed that a mul­ti­tude of neur­ons spe­cif­ic to cer­tain char­ac­ter­ist­ics of space col­lab­or­ate in this GPS. Some provide a spa­tial met­ric, oth­ers code the dir­ec­tion of move­ment, oth­ers the ori­ent­a­tion of the head, oth­ers sens­ory exper­i­ences. These highly soph­ist­ic­ated cir­cuits sup­port a fairly flex­ible rep­res­ent­a­tion sys­tem, enabling the anim­al to nav­ig­ate in space and men­tally map its envir­on­ment. My team and I hypo­thes­ise that a sim­il­ar sys­tem, highly com­plex and integ­rat­ing diverse inform­a­tion, is also deployed for time. This is what we are going to explore in the CHRONOLOGY project. 

CHRONOLOGY aims to under­stand how the brain maps time. One of our intu­itions is that the neur­al mech­an­isms that gen­er­ate the men­tal map­ping of time are largely com­mon to dif­fer­ent spe­cies. Each of us will there­fore be test­ing the rep­res­ent­a­tions of time in liv­ing mod­els from dif­fer­ent spe­cies: Brice Bathel­li­er from the CNRS in mice, Mehrdad Jaza­y­eri from MIT in non-human prim­ates and myself in humans. Srd­jan Ostojic, from the ENS, will build mod­els of low-rank recur­rent neur­al net­works, developed based on bio­lo­gic­al plaus­ib­il­ity, i.e. con­strained by the archi­tec­ture of the neur­al cir­cuits of the three spe­cies. Thanks to the back-and-forth between these AI approaches and the beha­vi­our­al exper­i­ments car­ried out on liv­ing mod­els, we hope not only to identi­fy the dynam­ics of the cereb­ral activ­ity at the ori­gin of our rep­res­ent­a­tion of time, but also to under­stand the caus­al links between the mech­an­isms involved.

We need this type of pro­ject, aimed first and fore­most at acquir­ing fun­da­ment­al prin­ciples that can be gen­er­al­ised across the anim­al king­dom, before tack­ling more applied ques­tions such as: why are cer­tain psy­chi­at­ric or neur­o­lo­gic­al dis­orders accom­pan­ied by tem­por­al dis­or­i­ent­a­tion? The brain is the most com­plex sys­tem in the uni­verse, even more com­plex than a star or a black hole – a star and black hole that it is itself cap­able of con­ceiv­ing! We still have almost everything to learn about how it works.

Interview by Anne Orliac

Find out more: 

• Run­y­un, Ş. L., van Wassen­hove, V., & Balci, F. (2024), Altéra­tion de la con­science tem­porelle pendant la pandémie de Cov­id-19, Recher­che psy­cho­lo­gique, 1–11.
• Kononow­icz, TW, Roger, C., & van Wassen­hove, V. (2019), La méta­cog­ni­tion tem­porelle comme décod­age de la dynamique cérébrale auto-générée, Cor­tex cérébral, 29 (10), 4366–4380.
• Grabot, L., & van Wassen­hove, V. (2017), L’ordre tem­porel comme biais psy­cho­lo­gique, Psy­cho­lo­gic­al sci­ence, 28 (5), 670–678.
• Gau­th­i­er, B., & van Wassen­hove, V. (2016), Le temps n’est pas l’espace : cal­culs de base et réseaux spé­ci­fiques au domaine pour les voy­ages men­taux, Journ­al of Neur­os­cience, 36 (47), 11891–11903.