Der Amrit, I do not fully understand your question. The constant routine method only seems to assess the existance of the circadian component, while the forced desynchrony protocol claims to estimate the quantified contribution of the circadian and homeostatic component. If you mean with timeof day experiment, a free-running rhythms protocol that allows sleep to occur at free-will, it will reveal the homeostatic and the circadian component combined, since the circadian rhythms will gate the homeostatic effects to a certain time of day.

greetz,

Roelof

Thanks Hunt! The point that you have mentioned is exactly that I was extensively searching for. When we use time-of-day method, according to literature, the effect of the two processes cannot be single out, yet, this method is the most preferred one given its ease of administration, simplicity and cost effectiveness. So, to find the influence/ contribution of ONLY circadian rhythms on cognitive performance, which method will you suggest amongst the three?

Furthermore Sir, can we have free-running rhythms in time-of-day protocol?

Hello Amrit,

Are you working human circadian rhythm or human chronobiology?

Hey Gaurav,

I am working on Human Circadian Rhythm (chronotype, precisely speaking) and its effect on cognitive performance on various cognitive domains, as of now! What about you? Working in same or adjacent field? 

@Amrit,

OK, now I start to better understand your aim.

It really depends on the question and not so much on the 'cost effectiveness' (good science is priceless, right?).

Here is the thing: the circadian system drives/gates many processes in the body. For instance metabolic rate, sleep, eating, and activity. If we would be interested in how the circadian system affects, say, body temperature (Tb), we would find that Tb is affected by all four parameters (metabolic rate, sleep, eating and activity). If you would be interested in the direct effects of eating per se on Tb, than you could compare a free-running CR (where people can have three meals or so) with a constant routine with isocaloric snacks. If you would be interested in the direct effect of sleep on Tb, one could compare a forced desynchrony study with a free-running time of day study or with a constant routine protocol (where there is constant sleep deprivation). One thing we cannot change directly and independently of the others, is metabolic rate. This means that in the forced desynchrony, behavoural parameters (sleep, activity, eating....but also things like showering) will all be cathegorized as 'homeostatic regulated' whereas all other parameters that are rather physiological linked to the circadian clock (like metabolic rate) will all be cathegorized as 'circadian regulated' because they are internally not/less dependent on sleep/wake behaviour.

However, in real life, the clock also drive sleep/wake behaviour, and therefore the parameters discussed above will all be synchronized and will all add up to form a ciricadian body temperature profile which can be shown in a 'time of day' free-running rhythms.

So the different protocols are really designed to isolate different contributions on a output measure down stream from the clock and downstream from sleep & behaviour....

I hope this helps...

greetings,

Roelof.

Dear Hut, got your point whole-heartedly & a big thanks for clearing many of the doubts! As you already know my aim (to find the influence/ contribution of ONLY circadian rhythms on cognitive performance), may you please give your valuable suggestion on which method to undertake? 

P.S:- Extant researches shows 'time-of-day' protocol to be the superior one for cognitive assessment (as already mentioned by me) & subsequently if I use this method, in the future my findings could be very well questioned given that not only circadian, but, homoeostatic influence will also be present affecting the cognitive performance of participants.

Hope you get my point!

Regards.

While both the forced desynchrony and the constant routine (with isocaloric snacks) are both considered gold-standards for dissecting circadian versus homeostatic influence, both can be costly as they require many consecutive days in the lab. One protocol that aims to alleviate these constraints is the ultradian sleep wake schedule (USW). It is often used by Dr. Boudreau and Dr. Schecter from the lab of Dr. Diane  Boivin at The Douglas Mental Health Institute of McGill. Let me know if you have trouble finding the papers. Essentially, patients are asked to observe a 1.5 hour light:dark/sleep:wake schedule (which forces circadian desynchrony as the time does not harmonize with 24 hours) whereby parameters are collected throughout. Then you can dissect both the influence of light and circadian rhythmicity around the clock while keeping sleep homeostasis stable. All without the need for keeping people in the lab for week-long stretches. I would imagine light levels would actually affect cognitive performance more than you might realize. This protocol will allow you to dissect that as well (unlike constant routine).

Dear Blum, thanks for bringing a whole new protocol into picture! Please help me with the papers. Besides,I have certain doubts :-

1. How many days participants have to be in the given schedule so as to ensure the viability of the experiment?

2. Please deliberate upon "the 1.5 hour sleep wake cycle". I mean its mechanisms. On the first impression, it resembles to that of forced desynchrony to me!

Regards. 

1. I attached a couple papers that should help. In general people are using a 72hr protocol regardless of whether it is designed to also include forced desynchrony or not.

2. I actually couldn't quickly find something from the Boivin lab that did both ultradian and forced desynchrony so I attached a Kripke paper where they used 1 hour wake, 0.5 hour nap. As you can see, because the cycles do not harmonize with 24 hours it acts similarly to forced desynchrony so that a full day falls outside the range of human entrainment (28hrs). So this protocol is kinda of a best of both worlds. 

http://www.ncbi.nlm.nih.gov/pubmed/16147900

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3825442/

thank you so much Blum!