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.