Thanks Joachim for the links. Particularly that the hippocampus has time cells that keep account of the passing time. yes, indeed, they already have "place" cells to keep track of spatial events, but this neurocellular timing mechanism is an interesting one as the experiments performed by Eichebaum research group demonstrates. But often, some pathological conditions result in temporal disorientation as we loose track of the passing time.

This is interesting in the other sense that we have a biological time machine, say "time cells" right inside our brain that might help us understand how our mind works in such spatio-temporal dimensions. So, one question comes to my mind;

Does memory depend on time? is it programmable or say, if rats are homogenized by removing those time cells, will they loose their temporal orientations? Are those time cells, called time neurons isolated just like mirror neurons?

One more question that i beg;

since those 'time cells' in the hippocampus keeps track of moments, removing or altering these temporal cells or by reprogramming those by surgical implants will perhaps hold back aging, Or it may not be...

Much thanks again,

Regards, Sidharta

You have to dig into the circadian rhythms (CRs) research to understand the background for this question. For one thing there is an important region of the brain that appears to regulate CRs. This region is called the suprachiasmatic nucleus (SCN) of the mammalian hypothalamus. Some of the original studies about how the brain processes time were conducted in caves by French researchers who wanted to see what would happen if one cut off all the normal solar and lunar cues.

Here is an observation and question with which I have challenged students and colleagues over the years: Many have experienced the ability to awaken moments before a new setting on the bedside alarm actually buzzes. What could possibly generate such a precise internal arousal signal?

Part of the problem is defining what we mean by time. We all know what time is, but we also have a hard time defining it. One thing all definitions seem to require is a changing pattern of inputs.

The other problem is thinking of the brain as a single organ where all parts have been shaped by the same selection pressures. One way of looking at time is as the adaptation of different brain modules each dealing with different types of changing, but somewhat predictable, patterns.

Clearly, one of the most obvious change patterns is light/dark (day/night). The brain modulates the metabolic functions of the various organs to optimize resource conservation and expenditures to the activity patterns of the species (when are the optimum times to find food versus minimizing exposure to predation). This also applies to annual cycles with hot/cold and wet/dry seasons. We perceive these recurring cycles as one aspect of time.

Another aspect of time comes from one of the modes of Hebb’s Rule. If neurons are activated together in a sequential pattern their axon/dendrite connections strengthen in a “directional” manner. This is the basis of our perception of cause and effect, but this predictable sequence of changes is also another aspect of our perception of time. You can’t have cause and effect without a concept of time (one event happens before another in time because one neuron fires before the other in time).

At an atomic and molecular level certain changes also occur at predictable (mass action) rates. This is the basis of time used for our modern atomic clocks because the rate of change is even more precise than circadian changes. Neurons (and other autorhythmic cells) that have timer functions use this same molecular, mass action, mechanism. An example is the SA node (pacemaker cells) in the heart. They depolarize at a predictable rate based on the diffusion rate of sodium ions through leak channels.

The ability to unconsciously track and anticipate when an alarm will go off is likely due to some interplay between the circadian and mass-action timing neurons. The interaction could be prewired to some extent, although some of the cultural differences in time perception indicate it is more likely a learned connection.

The conscious perception of the rate of time passing is another issue that I find even more intriguing. We all know that when we are completely engaged in an activity we “lose track of time.” In these states we perceive time as flying by. The less engaged in an activity we are, the slower time is perceived as passing. So time perception also appears to be not only a function of but also a key element of consciousness. Perhaps this is because the more engaged in activity we are, the faster our neural patterns are changing. Once again time and rate of input pattern changes appear to be tightly coupled.

Our brain has several references to record time. First, the frequency of alpha wave or other brain cell wave. Second, the frequency of the heart beat, third the respiratory rate, and many other processes in our body that have cyclic processes. All of these frequencies if change by our body activities, will be brought again to the normal reference. Also night and day cycle can be used as reference by our brain. We know that our brain is intelligence. It must could detect time precisely. Not only machine is intelligence.

One must also consider the scale of time perception, as Steven mentioned several different levels of it, these work on different scales of time (compare the very different sub second-to-second range to that of daily rythm and to "years of memories" - which most of the times having an imprecise "time stamp") years and I would be hugely surprised if there was a "single neural mechanism" behind all that.

The conscious "now" that separates the past (registered as memories) and future (registered as extrapolation of memories) can have a different length, dependent on the state we are in. The "time flying by" phenomenon may simply be result of us not paying attention to the perception of time passing by. Perception of the "now" and how fast time goes by can change a lot when people meditate or during a fight or flight reaction when time seems to slow down (compared to our own though processes, even our own adrenalin-sped body may seem to be lagging behind the will to move). I'd argue that the more the brain is "sped up", the more we are able to consciously experience, the slower time may seem to flow, as there is a larger number of "nows" per second. The "sense" of how fast time is flowing may however not be very different for two people with very different "brain speeds" - it would be "normal" for both of them. It's when the state of the mind changes (and affects speed) we may sense that time flows at a different speed.

An interesting question that I've been musing about is how the conscious "now's" length affects (or is affected) with the brain's ability to process sensory information. Our ability to see and react to the visual environment has a temporal side to it - would it be possible to see "faster" (have better temporal resolution)? Is the "now" shorter (and thus there is more of it per second) in animals that have faster temporal resolution, like birds? To fly between branches of trees they have to be able to see and process what they see at a faster pace than what we need in order to not knock our head into a tree while running - and yes, they do have a much higher than human "flicker fusion frequency". But does this mean that in their relatively shorter life-span they can and do actually perceive more?

I've also considered this question . They surely do perceive more, but perhaps the faster temporal resolution extends their perception of the passage of time. Do they perceive us as moving in 'slow motion', for instance?

Considering human perception of time on a longer scale, we only know the amount of time we have lived. Other time frames are an abstraction relative to that experience. If you are five years old, five years in the future seems a lifetime (because it is). If you are fifty years old, five years in the future does not seem quite as far away (it is now 10% rather than 100% of the experienced lifetime). Do children also perceive the passage of hours and minutes as passing more slowly than a fifty year old because an hour is a much larger percentage of their experienced life?

Steven’s response leads me to ponder over the point “is time is processed by our brain?” If it is true then time is relative, but the question pointedly raised by Steven, “Do children also perceive the passage of hours and minutes as passing more slowly than a fifty year old because an hour is a much larger percentage of their experienced life?” leads me to think that time is absolute although, we measure it in some quantity of rotation an revolution of the Earth at its axis and around the Sun. If intelligent life exists somewhere deep in the universe its reference to measure time may be different from ours. If time is relative and processed by our mind then why scientists are reported to build a 4-D crystal clock discrete in time and space that will tick even when, as per current Nobel Prize awarded theory of cosmos, light energy would exhaust and universe would turn into cold wasteland. I don’t think that by that time there would exist the Sun or the Earth or even they would exist there would be no rotation or revolution. Who would return to know what time had passed? Not denying the fact the proposed clock also had some temporal purposes for the scientists, if they long or their follower live to see the results or current cosmological theories of space-time take a new turn and scientists instead of becoming bigots become more receptive of till now non-scientific concepts.

Steven, many human estimations are proportional so it seems reasonable it would relate to time too. A recent study I've published reports how adolescents recall numbers of events as ratios (by using a logarithmic mental scale, that is) . This is why estimates when regressed against acutality are only linear once they are log transformed. The same applies to estimating a number of observed objects. The consequence is that large numbers (and maybe long periods) are somewhat compacted and perceived as smaller (the equivalent would be shorter).

Yes, indeed. From what I've read of the research it does seem that this is reflecting the process at the synaptic level. There's some very interesting research - check out Piazza M, Izard V, Pinel P, et al. Tuning curves for the approximate numerosity in the human intraparietal sulcus. Neuron. 2004;44:547-55.

Even if perception is slower, the reactions must be also - hence the high rate of drug takers amongst those having driving accidents

One thing to add to this discussion: Is the perceived time the same as the time used in visually guided actions? It seems that this isn't the case. See Marinovic & Arnold (2012) Separable temporal metrics for time perception and anticipatory actions, for experimental evidence. In this case, time should be considered relative to the system that is estimating it. Time perception seems to be susceptible to a number of factors, while time for action doesn't seem to be affected.

Dear Daya Gupta,

The incident you are reporting is particularly a form of altered perception. When someone consumes "bhang" or cannabis, the neurons fire at a much higher threshold which often fails to perceive/sense the immediate stimuli, responses. They do not fire synchronously to say in simple sense. The active ingredients, here, THC (tetrahydrocannabinol) depresses the CNS neurons to such extent which distorts the normal mechanism of perception. That doesn't indicate that one might run "slow" or "conquer" time by consuming cannabis or sort of abusive substances. The perception threshold is altered, rather, neurons often misfire.

Accompanying such altered perception of light, sound or time,smell are hallucinations, euphoria or other mental states which depress memory formation and recall (impaired procedural memory related skill). Time perception is hence depressed. The changes are purely subjective. Generalised CNS

depression, drowsiness, sleep etc, symptoms are observed in such subjects. The role of endocannabinoid system is also a major cause of depression. Temporal integration of the subjective mind with the objective world is affected by "bhang". So do the attentional mechanisms which gets distorted too. Yes, your point is interesting as of how time perception gets altered in such subjects under drug abuse.

See:

http://www.pnas.org/content/109/40/15970.full?sid=6ca001cf-22a8-460b-8a0f-e34667fe6316

http://www.sciencedirect.com/science/article/pii/0926641096000092

Sincerely,

Sidharta

The higher threshold is due to the fact that cannabis markedly increases dopaminergic neuronal firing which include "burst fire."

Ref:

http://www.nature.com/nrn/journal/v8/n11/abs/nrn2253.html

We know to some extent 'why' time perception is altered, but 'how' is it altered is perhaps more interesting area for investigation. The reason I presume that their might be some time processing system (network of neurons) inside the brain that couples subjective states of time perception with the outside world. We know about circadian rhythms, but I think its not purely the same theory which is behind temporal integration. A new research states that cannabinoids desynchronize neuronal "assemblies", which also probably impair memory related functions that affect the hippocampal system.

Ref:

http://www.nature.com/neuro/journal/v9/n12/full/nn1206-1461.html

There has been a lot of research showing a .3 msec to longer delay between sensory input and perception in the brain. One of the reasons proposed is that when a multi-sensory event happens it takes different lengths of time for each sense to get to the integration center. Therefore, the inputs have to be "tagged' somehow to put the correctly associated event inputs together into a multi-sensory whole. This is similar to the problem a computer processor has, that is solved by the clock timings that are set to intervals (measured in megahertz) that accommodate the arrival of the slowest input. Perhaps one aspect of our perception of time arises from the way our brain handles this necessity of accommodating these multi-sensory timing issues to properly perceive the whole event. Of course this whole event representation in our brain is what we call (perceive as) reality. When we alter these timings, our perception of reality also gets altered.

There is book in Bulgarian written by professor Leon Mitrani and Stefan Shekerdjiiski " The time" that suggest that time is encoded by the brain by different motor commands. I think that this might be one of the functions of the mirror neurons.

Hi Sidharta,

This is a complex question, with no one correct answer. The proponents of the "centralised" or dedicated models of timing control come from a modular perspective and there is plenty of evidence to support this modularity. For example, particular diseases such as Parkinson's disease or Huntington's disease have specific effects on parts of the timing system (the basal ganglia) with subsequent effects on time processing (e.g. Harrington et al 1998). Similarly brain damage to specific modules of the time processing network have specific effects on timing, with lesions to the cerebellum affecting subsecond timing (depending on the locus of the damage). Neurotransmitters affected by particular drugs are also known to differentially affect parts of the timing mechanism (see Rammsayer's articles on this). So there is evidence to suggest that some aspects of timing control are processed in particular areas of the brain.

On the other hand, state-dependent or intrinsic models of timing recognise that the communication unit of the brain is the neuronal oscillation which codes for temporal perceptions. This oscillatory activity produced by populations of neurons firing together has been found to relate to the size of temporal intervals or the start/end points of intervals. These models suggest that (as in many other biological systems) it is the dynamic properties of the system that give rise to behaviour.

The two models are therefore different approaches to the same problem and a combination of the two will most likely be most successful as a model of temporal processing.

Hi Sidharta,

you can see by the above that it is very much an open question, as are a most of questions about brain functioning. Don't go looking for absolutes, you'll just get frustrated. Following up from Emma's comments, here is an article that I found helpful on several levels: Buonomano, D. V., & Laje, R. (2010). Population clocks: motor timing with neural dynamics. Trends in Cognitive Sciences, 14(12), 520-527.

cheers

Adam

When someone practices a groove activity with a precise timing, it is very quickly able to leave out this activity without looking at his (her) watch. So I guess the first answer seems to be more probable. But our brain is so complex !!!

Yes thanks for all your answers. What i mean by our brain processing time is how it perceives time. Is it an illusion or real passing of events…that we are not able to perceive time when we are in sleep. Only a wakeful mind is aware of time but may not be always attentive. This relative aspect creates problem since time is related to brain cell or neuronal learning and conditioning. Time is also related to ageing. If the active process of how our brain process time is known we can have something to say about such perception-oriented aging. What i believe this is not illusion.

maybe this would be of help....although not directly related to your question

From Signals to Patterns: Space, Time, and Mathematics in Developmental Biology- http://www.sciencemag.org/content/322/5900/399.full?sid=2ddf3a46-c9f7-4a4f-a02d-9e1f601e0dee

It is not true that we are not accounting for time and/or durations during our sleep. I do not know the scientific researches about this topic, but the common experience is that many people are able to wake up, in particular circumstances, at the precise time their purpose needs.

Dr. Bernard,

Yes I understand that our brain doesn't loose track of time while we are n sleep, that's circadian rhythm. But there are document research regarding patients loosing this rhythm with ageing.

http://m.genesdev.cshlp.org/content/17/11/1366.long

Best Regards,

Sidharta

Dear Daya Gupta,

Your answers are interesting. Perhaps need to have a deeper look into such time control processes inside the brain-I would say, time processng biological clocks you have mentioned.

Regards,

Sidharta

Neural activity in relation to temporal distan Differences in past and future temporal discounting Original Research Article

Consciousness and Cognition, Volume 21, Issue 4, December 2012, Pages 1662-1672

J.M. He, X.T. Huang, H. Yuan, Y.G. Chen

Highlights

► Neural activity in past temporal discounting differed in delay paradigms. ► The peak amplitudes of P2 and P3 varied with the past temporal distance. ► No significant differences were found between past 5years and 50years. ► Neural activity in future temporal discounting differed in interval paradigms. ► Conditions (6months:5years) and (6months:50years) had influence on P2 and N2.

Check this out (attached).

Here is a paper about "frames of sensory information". (Frames were provided by pulses of vibration.)

I believe much of the complexity of the question arises from the "definition" of time itself. In fact, as far as biological and cognitive aspects are concerned, there are at least three very different aspects of time to be considered:

1) time as a separation between two subsequent events (or pace in a series of events);

2) time as a "continuous flow" in perception / cognition

3) time as a perceived distance in the past (or future)

1) In terms of separation between two events, the question is again three-fold:

- short time intervals, and the capability of discerning two non-perfectly synchronous events

- "medium" time intervals (in the order of seconds)

- prolonged time intervals (in the order of minutes/hours)

As regards short time intervals, it should be considered that - although only few spikes can be discharged in few ms, and it is therefore virtually impossible for neurons to be able to recognize a modulation in spike firing rate over a few ms period - neuronal circuitries make it possible to introduce variable delays (from about 1 ms when a synapse is introduced in a circuit, down to nonsensical fractions of a ms when differences of less than one mm of axonal length are involved). Since the detection of coincidence between two signals may be particularly efficient, very tiny time intervals can be discerned: consider, for example, that the owl (which has to localize its prey in the dark) can precisely distinguish the direction from which a sound arrives thanks to a series of coincidence detectors (neurons) that are horizontally aligned, each of them receiving the sensory information from the two ears with a very slight difference in delay (

An interesting approach of brain and time is the question of circadian rhythms. They are depending on an internal clock and atmospheric external circumstances.

The internal clock is biochemically and genetically determined. I suggest that the neuronal "circuitry" is involved (loop information processes) in the genetic determination,

Probably the only aspect of time that is available to living organisms is the synchronisation of circadian and circannual rhythms to the environmental cycles. These control the time of feeding, sleeping, foraging, locomotor activity and other aspects of behaviour, as well as metabolic activity and hormonal release related to such behaviour. The perception of period/frequency is available through the auditory system. Time perception such as the one involved in keeping the time in music etc, are probably the result of extensive training and probably not available to a child or an untrained person. The null hypothesis ought to be that there are no correlates of time perception in the activity of neurons in an average untrained person and in most animals.

Neuronal activity varies over time. Otherwise we wouldn't know about time! What people don't appreciate sufficiently is that the way the brain processes time is in terms of phase. Time should not be thought of as one-dimensional, a common Western notion, but as most of the world thinks, as a disc, with points corresponding to period/frequency and phase. Nearby points in this space can be separated on the line: for example mornings, Fridays, summers, ....

Neurons do not fire at times on the line (1960s cells) but instead they fire at certain phases with respect to stimuli, actions, and behaviors. The brain creates populations of neurons with differing timings, and then puts them together systematically to signal direction. What we usually want to know is the direction in which things change. Our behaviors are ordered in time.

To get direction, the brain needs to have timings that differ by about a quarter cycle. The way I illustrate this is to ask how you would move from 12 to 6 on a clock. You can do this equally well in either direction, clockwise or counterclockwise. If I instead tell you to move from 12 to 6 through 3, you will probably go clockwise. By having cells that fire about a quarter cycle apart for various processes, we detect and act in a direction selective manner.

Most of our behaviors take place over relatively long time scales, seconds and longer. This challenges the usual view of neuronal processing, where people attend to millisecond scales. How do neurons get timing differences over these long time scales?

Our work provided an example of how this may work throughout the brain. In the geniculocortical pathway, direction selectivity is created in primary visual cortex by putting together geniculate inputs that have timing that differs by about a quarter cycle. The retina creates timing differences across sustained and transient ganglion cells, and these timing differences persist through LGN and cortex, providing the substrate for cortical direction selectivity at high temporal frequencies. However, a circuit in LGN that is also found throughout thalamus creates lagged cells with timing shifted by about a quarter cycle at low frequencies (Saul & Humphrey, 1990). Lagged and nonlagged cells converge on certain cells in cortex to generate direction selectivity at low frequencies (Saul & Humphrey, 1992b). In cat visual cortex, direction selectivity is seen predominantly at low frequencies, matching the prediction based on convergence of lagged and nonlagged inputs (Saul & Humphrey, 1992a). In monkey, lagged cells are also seen in LGN (Saul, 2008), but lagged and nonlagged cells in monkey are a quarter cycle apart over a wider range of frequencies. This corresponds with the temporal frequency dependence of direction selectivity (Saul et al., 2005).

Because the circuit that creates lagged cells in LGN exists throughout thalamus, I speculate that thalamus changes timing of the various inputs to cortex, and can do so even at very low temporal frequencies. For example, limbic inputs to prefrontal cortex that are modulated over many minutes can be shifted in mediodorsal thalamus to provide PFC the quarter cycle differences needed to modulate our behavior over these time scales.

Temporal processing varies widely across individuals. We all know people who are always late, and others who do things ahead of time. More pathological conditions are well-known, such as Paula Tallal's Specific Learning Impairment work, where children don't adequately process rapid changes. ADHD could be the opposite problem of not doing well with sustained processing. It seems worthwhile to consider the possibility that individuals vary in the populations of sustained, transient, and lagged cels in thalamus, since these neurons vary not just functionally but also structurally and could be defective across thalamic nuclei.

Here's a review in case you're interested in some details.

Oxidized quinones signal onset of darkness directly to the cyanobacterial circadian oscillator

Yong-Ick Kima, David J. Vinyardb, Gennady M. Ananyevb, G. Charles Dismukes, and Susan S. Golden

It seems to me that assessing a time span might be processed along two ways (eventually interconnected). The first mean is to evaluate "roughly"

and the second one to better tune this first evaluation !

See :

Stella F. Lourenco et al. (2012), Nonsymbolic number and cumulative area representations contribute shared and unique variance to symbolic math competence

Humans and nonhuman animals share the capacity to estimate, without counting, the number of objects in a set by relying on an approximate number system (ANS). Only humans, however, learn the concepts and operations of symbolic mathematics. Despite vast differences between these two systems of quantification, neural and behavioral findings suggest functional connections. Another line of research suggests that the ANS is part of a larger, more general system of magnitude representation...

Http://www.dosenation.com/listing.php?smlid=4301

In my preschool class I demonstrated that time is a measure of change. My preschoolers got it immediately. I got this idea from Julian Barbour's book, The End of Time.

Time is a river between concepts and individuals (objects). Kant called all this package "trascendental schema", in his Kritik der reinen Vernunft. This time, I think, is not a linear time, it is a time that does "grow", like a plant that growing does change its form. I think of a morphological time.

Time is fix. The universe, including us, are in changing process, are aslways circulate. The brain not necessary to process time, because the brain it self is in changing process.. Time is fix, but the watch is always running.

Dear Sutarmo,

from a physical-mathematical point of view I think time in the sense of Prigogine's internal time (T) that is an "operator". I think you are instead thinking of Newton concept of time (t), i. e. the time of mechanics. Ontologically, Newton did mean with time the "duration"(Naturalis philosophiae principia). It is an homogeneous time that does flow in an uniform way and that is in relation with the mouvement. Mouvement for Newton is the true measure of time. Prigogine's T is an operator working at level of unstable dynamic systems... I did before talk about philosophical concept of time and I did have in my mind time in biological processes where "internal time" (T) concept would be more appropriate also if not perfect...

Here is an interesting contribution to our thread !

Erik P. Cook, Christopher C. Pack,

Parietal Cortex Signals Come Unstuck in Time

==> This primer describes research by Blaine Schneider and Geoffrey Ghose, which shows that neuronal activity in the lateral intraparietal cortex of monkeys reflects the passage of time, and is sufficiently precise to explain timed eye movements.

In this question it would be interesting to ask how the brain is processing music.

I found an article talking about CA1 of the hippocampus encoding time intervals. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=23132944

Perhaps followers of this question would be interested in contributing to the Research Topic I am hosting at Frontiers-- here is the link

http://www.frontiersin.org/Perception_Science/researchtopics/The_long_and_short_of_mental_t/2182#

Time is a vector that is always monotonically ascending.

The biological, cognitive, and logical clocks of humans are formally modeled in: “Formal Descriptions of the Cognitive Processes of Spatiality, Time, and Motion Perceptions,” International Journal of Cognitive Informatics and Natural Intelligence, 3(2), 84-98, [Wang, 2009].

It seems that the brain does not consciously process time or anything. The brain is the cite for processing which s different from the knower who knows the result of processing. Frequency of neural processes in the brain is the important factor. We are not the brain, although we use the wonderful instrument called the brain for processing to get any kind of knowledge , including time.

Recent studies shown that there are some "time cell" in hippocampus which fire at particular moment during our behavior (Benjamin J. Kraus 2013). This maybe be a key word for finding the answer.