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.