One of the most obscure -racetams around, coluracetam (Smarter Nootropics, Ceretropic, Isochroma) acts in a different way from piracetam - piracetam apparently attacks the breakdown of acetylcholine while coluracetam instead increases how much choline can be turned into useful acetylcholine. This apparently is a unique mechanism. A crazy Longecity user, ScienceGuy ponied up $16,000 (!) for a custom synthesis of 500g; he was experimenting with 10-80mg sublingual doses (the ranges in the original anti-depressive trials) and reported a laundry list of effects (as does Isochroma): primarily that it was anxiolytic and increased work stamina. Unfortunately for my stack, he claims it combines poorly with piracetam. He offered free 2g samples for regulars to test his claims. I asked & received some.
Certain B vitamins - B6, B12 and folic acid - are known to reduce levels of a compound called homocysteine in the blood. Elevated levels of homocysteine are associated with increased risk of stroke, cognitive impairment and Alzheimer's disease. A study of a group of elderly patients with mild cognitive impairment found that after two years of intervention with high doses of B6, B12 and folic acid there was significantly less brain shrinkage compared to a subset given placebo treatment. Opt for B-rich foods like eggs, chicken, fish and leafy greens.
“We didn’t see significant long-term effects from the dosage used,” said Wen-Jun Gao, a professor of neurobiology at the Drexel University College of Medicine, and one of the authors of the study. He added that the brain doesn’t fully stop developing until age 25 or 30, making cognitive enhancement potentially risky even for users who are well into adulthood.
Chatterjee told me that many people who come to his clinic are cognitively preoccupied versions of what doctors call the "worried well". He had just seen a middle-aged woman, a successful Philadelphia lawyer, who mentioned having to struggle a bit to come up with certain names. "Here's an example of someone who by most measures is doing perfectly fine," Chatterjee said. "She's not having any trouble at work. But she notices she's having some problems, and it's very hard to know how much of that is just getting older." Of course, people in her position could strive to get regular exercise and plenty of intellectual stimulation, both of which have been shown to help maintain cognitive function. But maybe they're already doing so and want a bigger mental rev-up, or maybe they want something easier than sweaty workouts and Russian novels: they want a pill.
“It is surprising and encouraging that it may be possible to predict the magnitude of a placebo effect before treatment,” says Tor Wager, a neuroscientist at the University of Colorado Boulder, who was not involved in the research. More work is needed to see how the predictive features hold up in other populations and for different pain conditions, he says.
There are a number of treatments for the last. I already use melatonin. I sort of have light therapy from a full-spectrum fluorescent desk lamp. But I get very little sunlight; the surprising thing would be if I didn’t have a vitamin D deficiency. And vitamin D deficiencies have been linked with all sorts of interesting things like near-sightedness, with time outdoors inversely correlating with myopia and not reading or near-work time. (It has been claimed that caffeine interferes with vitamin D absorption and so people like me especially need to take vitamin D, on top of the deficits caused by our vampiric habits, but I don’t think this is true35.) Unfortunately, there’s not very good evidence that vitamin D supplementation helps with mood/SAD/depression: there’s ~6 small RCTs with some findings of benefits, with their respective meta-analysis turning in a positive but currently non-statistically-significant result. Better confirmed is reducing all-cause mortality in elderly people (see, in order of increasing comprehensiveness: Evidence Syntheses 2013, Chung et al 2009, Autier & Gandini 2007, Bolland et al 2014).
Rather than cause addiction, the nootropic choline may help to treat this illness. Choline helps to increase dopamine levels. In cocaine users, for instance, dopamine levels are lowered. Taking choline potentially helps those recovering from cocaine abuse to feel better and experience fewer cravings. Research in this area is limited, but it is promising.
Nootropics still exist largely in an unregulated gray area, which makes users somewhat hesitant to discuss their regimens. But I did speak to several people who told tales of increased productivity and sharpened focus. Bob Carter, a financial analyst for a start-up called LendingHome, says that nootropics have replaced his other morning stimulant. “I basically think of it as a substitute for coffee,” he says. “I think the problem with a cappuccino from Starbucks is that it gives you the feeling of being jittery. Whereas with this particular supplement, I feel more calm.”
And yet when enthusiasts share their vision of our neuroenhanced future it can sound dystopian. Zack Lynch, of NeuroInsights, gave me a rationale for smart pills that I found particularly grim. "If you're a 55-year-old in Boston, you have to compete with a 26-year-old from Mumbai now, and those kinds of pressures are only going to grow," he began. Countries other than the US might tend to be a little looser with their regulations and offer approval of new cognitive enhancers first. "And if you're a company that's got 47 offices worldwide, and all of a sudden your Singapore office is using cognitive enablers, and you're saying to Congress: 'I'm moving all my financial operations to Singapore and Taiwan, because it's legal to use those there', you bet that Congress is going to say: 'Well, OK.' It will be a moot question then.
Caveats aside, if you do want to try a nootropic, consider starting with something simple and pretty much risk-free, like aromatherapy with lemon essential oil or frankincense, which can help activate your brain, Barbour says. You could also sip on "golden milk," a sweet and anti-inflammatory beverage made with turmeric, or rosemary-infused water, she adds.
If you want to focus on boosting your brain power, Lebowitz says you should primarily focus on improving your cardiovascular health, which is "the key to good thinking." For example, high blood pressure and cholesterol, which raise the risk of heart disease, can cause arteries to harden, which can decrease blood flow to the brain. The brain relies on blood to function normally.
When taken regularly, Vitacern Brain Focus Supplement can help your mind function at its best for noticeable improvements in brain power. Our brain supplement promotes better concentration and improved focus to help you excel at work or school. In addition, our focus supplement aids in brain health throughout life for clearer thinking and memory support.
Choline is a nootropic: it enhances your ability to pay attention and learn efficiently, probably because you use a lot of acetylcholine during mentally-demanding tasks, and choline helps you synthesize enough to work harder and go longer. Choline also links to decreased brain inflammation in a dose-dependent manner — the more choline you eat, the less inflamed your brain tends to be.
20 March, 2x 13mg; first time, took around 11:30AM, half-life 3 hours, so halved by 2:30PM. Initial reaction: within 20 minutes, started to feel light-headed, experienced a bit of physical clumsiness while baking bread (dropped things or poured too much thrice); that began to pass in an hour, leaving what felt like a cheerier mood and less anxiety. Seems like it mostly wore off by 6PM. Redosed at 8PM TODO: maybe take a look at the HRV data? looks interestingly like HRV increased thanks to the tianeptine 21 March, 2x17mg; seemed to buffer effects of FBI visit 22 March, 2x 23 March, 2x 24 March, 2x 25 March, 2x 26 March, 2x 27 March, 2x 28 March, 2x 7 April, 2x 8 April, 2x 9 April, 2x 10 April, 2x 11 April, 2x 12 April, 2x 23 April, 2x 24 April, 2x 25 April, 2x 26 April, 2x 27 April, 2x 28 April, 2x 29 April, 2x 7 May, 2x 8 May, 2x 9 May, 2x 10 May, 2x 3 June, 2x 4 June, 2x 5 June, 2x 30 June, 2x 30 July, 1x 31 July, 1x 1 August, 2x 2 August, 2x 3 August, 2x 5 August, 2x 6 August, 2x 8 August, 2x 10 August, 2x 12 August: 2x 14 August: 2x 15 August: 2x 16 August: 1x 18 August: 2x 19 August: 2x 21 August: 2x 23 August: 1x 24 August: 1x 25 August: 1x 26 August: 2x 27 August: 1x 29 August: 2x 30 August: 1x 02 September: 1x 04 September: 1x 07 September: 2x 20 September: 1x 21 September: 2x 24 September: 2x 25 September: 2x 26 September: 2x 28 September: 2x 29 September: 2x 5 October: 2x 6 October: 1x 19 October: 1x 20 October: 1x 27 October: 1x 4 November: 1x 5 November: 1x 8 November: 1x 9 November: 2x 10 November: 1x 11 November: 1x 12 November: 1x 25 November: 1x 26 November: 1x 27 November: 1x 4 December: 2x 27 December: 1x 28 December: 1x 2017 7 January: 1x 8 January: 2x 10 January: 1x 16 January: 1x 17 January: 1x 20 January: 1x 24 January: 1x 25 January: 2x 27 January: 2x 28 January: 2x 1 February: 2x 3 February: 2x 8 February: 1x 16 February: 2x 17 February: 2x 18 February: 1x 22 February: 1x 27 February: 2x 14 March: 1x 15 March: 1x 16 March: 2x 17 March: 2x 18 March: 2x 19 March: 2x 20 March: 2x 21 March: 2x 22 March: 2x 23 March: 1x 24 March: 2x 25 March: 2x 26 March: 2x 27 March: 2x 28 March: 2x 29 March: 2x 30 March: 2x 31 March: 2x 01 April: 2x 02 April: 1x 03 April: 2x 04 April: 2x 05 April: 2x 06 April: 2x 07 April: 2x 08 April: 2x 09 April: 2x 10 April: 2x 11 April: 2x 20 April: 1x 21 April: 1x 22 April: 1x 23 April: 1x 24 April: 1x 25 April: 1x 26 April: 2x 27 April: 2x 28 April: 1x 30 April: 1x 01 May: 2x 02 May: 2x 03 May: 2x 04 May: 2x 05 May: 2x 06 May: 2x 07 May: 2x 08 May: 2x 09 May: 2x 10 May: 2x 11 May: 2x 12 May: 2x 13 May: 2x 14 May: 2x 15 May: 2x 16 May: 2x 17 May: 2x 18 May: 2x 19 May: 2x 20 May: 2x 21 May: 2x 22 May: 2x 23 May: 2x 24 May: 2x 25 May: 2x 26 May: 2x 27 May: 2x 28 May: 2x 29 May: 2x 30 May: 2x 1 June: 2x 2 June: 2x 3 June: 2x 4 June: 2x 5 June: 1x 6 June: 2x 7 June: 2x 8 June: 2x 9 June: 2x 10 June: 2x 11 June: 2x 12 June: 2x 13 June: 2x 14 June: 2x 15 June: 2x 16 June: 2x 17 June: 2x 18 June: 2x 19 June: 2x 20 June: 2x 22 June: 2x 21 June: 2x 02 July: 2x 03 July: 2x 04 July: 2x 05 July: 2x 06 July: 2x 07 July: 2x 08 July: 2x 09 July: 2x 10 July: 2x 11 July: 2x 12 July: 2x 13 July: 2x 14 July: 2x 15 July: 2x 16 July: 2x 17 July: 2x 18 July: 2x 19 July: 2x 20 July: 2x 21 July: 2x 22 July: 2x 23 July: 2x 24 July: 2x 25 July: 2x 26 July: 2x 27 July: 2x 28 July: 2x 29 July: 2x 30 July: 2x 31 July: 2x 01 August: 2x 02 August: 2x 03 August: 2x 04 August: 2x 05 August: 2x 06 August: 2x 07 August: 2x 08 August: 2x 09 August: 2x 10 August: 2x 11 August: 2x 12 August: 2x 13 August: 2x 14 August: 2x 15 August: 2x 16 August: 2x 17 August: 2x 18 August: 2x 19 August: 2x 20 August: 2x 21 August: 2x 22 August: 2x 23 August: 2x 24 August: 2x 25 August: 2x 26 August: 1x 27 August: 2x 28 August: 2x 29 August: 2x 30 August: 2x 31 August: 2x 01 September: 2x 02 September: 2x 03 September: 2x 04 September: 2x 05 September: 2x 06 September: 2x 07 September: 2x 08 September: 2x 09 September: 2x 10 September: 2x 11 September: 2x 12 September: 2x 13 September: 2x 14 September: 2x 15 September: 2x 16 September: 2x 17 September: 2x 18 September: 2x 19 September: 2x 20 September: 2x 21 September: 2x 22 September: 2x 23 September: 2x 24 September: 2x 25 September: 2x 26 September: 2x 27 September: 2x 28 September: 2x 29 September: 2x 30 September: 2x October 01 October: 2x 02 October: 2x 03 October: 2x 04 October: 2x 05 October: 2x 06 October: 2x 07 October: 2x 08 October: 2x 09 October: 2x 10 October: 2x 11 October: 2x 12 October: 2x 13 October: 2x 14 October: 2x 15 October: 2x 16 October: 2x 17 October: 2x 18 October: 2x 20 October: 2x 21 October: 2x 22 October: 2x 23 October: 2x 24 October: 2x 25 October: 2x 26 October: 2x 27 October: 2x 28 October: 2x 29 October: 2x 30 October: 2x 31 October: 2x 01 November: 2x 02 November: 2x 03 November: 2x 04 November: 2x 05 November: 2x 06 November: 2x 07 November: 2x 08 November: 2x 09 November: 2x 10 November: 2x 11 November: 2x 12 November: 2x 13 November: 2x 14 November: 2x 15 November: 2x 16 November: 2x 17 November: 2x 18 November: 2x 19 November: 2x 20 November: 2x 21 November: 2x 22 November: 2x 23 November: 2x 24 November: 2x 25 November: 2x 26 November: 2x 27 November: 2x 28 November: 2x 29 November: 2x 30 November: 2x 01 December: 2x 02 December: 2x 03 December: 2x 04 December: 2x 05 December: 2x 06 December: 2x 07 December: 2x 08 December: 2x 09 December: 2x 10 December: 2x 11 December: 2x 12 December: 2x 13 December: 2x 14 December: 2x 15 December: 2x 16 December: 2x 17 December: 2x 18 December: 2x 19 December: 2x 20 December: 2x 21 December: 2x 22 December: 2x 23 December: 2x 24 December: 2x 25 December: 2x ran out, last day: 25 December 2017 –>
Another promising "smart pill" is phosphatidylserine, or PS, a natural substance that helps cell walls stay pliable and is thought to boost the effectiveness of neurotransmitters, which relay brain signals. In a May 1991 study published in Neurology, neuroscientist Thomas Crook found that patients with age-associated memory impairment improved their scores on key performance tests after 12 weeks on PS. Yet more research is needed before doctors can know that the supplement is safe and effective.
There's no magic bullet to boost IQ or make you smarter -- but certain substances, like caffeine, can energize you and help you concentrate. Found in coffee, chocolate, energy drinks, and some medications, caffeine gives you that unmistakable wake-up buzz, though the effects are short-term. And more is often less: Overdo it on caffeine and it can make you jittery and uncomfortable.
The greatly increased variance, but only somewhat increased mean, is consistent with nicotine operating on me with an inverted U-curve for dosage/performance (or the Yerkes-Dodson law): on good days, 1mg nicotine is too much and degrades performance (perhaps I am overstimulated and find it hard to focus on something as boring as n-back) while on bad days, nicotine is just right and improves n-back performance.
Some nootropics users are hopeful that the drugs could be permanently “neuroprotective”—in other words, that the compounds could slow down the neuronal aging process, and help avoid cognitive deterioration later in life. (For what it's worth, most of the users I spoke to said that didn't matter much to them. “I doubt anything I’ve tried has made me smarter in a long-term way,” Baker says. “That’s still science fiction.”)
With so many different ones to choose from, choosing the best nootropics for you can be overwhelming at times. As usual, a decision this important will require research. Study up on the top nootropics which catch your eye the most. The nootropics you take will depend on what you want the enhancement for. The ingredients within each nootropic determine its specific function. For example, some nootropics contain ginkgo biloba, which can help memory, thinking speed, and increase attention span. Check the nootropic ingredients as you determine what end results you want to see.
Brain enhancing drug – the steroids of the mental world, these are compounds that can be both artificial or natural that are not recommended for casual consumption. If taken over a long period of time, they can and will result in permanent and debilitating damage, and if taken wrongly, they can and will result in injury, illness, and death. So far from being the best brain pill that they loop around and punch the actual best brain pill in the face.
On the other metric, suppose we removed the creatine? Dropping 4 grams of material means we only need to consume 5.75 grams a day, covered by 8 pills (compared to 13 pills). We save 5,000 pills, which would have cost $45 and also don’t spend the $68 for the creatine; assuming a modafinil formulation, that drops our $1761 down to $1648 or $1.65 a day. Or we could remove both the creatine and modafinil, for a grand total of $848 or $0.85 a day, which is pretty reasonable.
Took full pill at 10:21 PM when I started feeling a bit tired. Around 11:30, I noticed my head feeling fuzzy but my reading seemed to still be up to snuff. I would eventually finish the science book around 9 AM the next day, taking some very long breaks to walk the dog, write some poems, write a program, do Mnemosyne review (memory performance: subjectively below average, but not as bad as I would have expected from staying up all night), and some other things. Around 4 AM, I reflected that I felt much as I had during my nightwatch job at the same hour of the day - except I had switched sleep schedules for the job. The tiredness continued to build and my willpower weakened so the morning wasn’t as productive as it could have been - but my actual performance when I could be bothered was still pretty normal. That struck me as kind of interesting that I can feel very tired and not act tired, in line with the anecdotes.
28,61,36,25,61,57,39,56,23,37,24,50,54,32,50,33,16,42,41,40,34,33,31,65,23,36,29,51,46,31,45,52,30, 50,29,36,57,60,34,48,32,41,48,34,51,40,53,73,56,53,53,57,46,50,35,50,60,62,30,60,48,46,52,60,60,48, 47,34,50,51,45,54,70,48,61,43,53,60,44,57,50,50,52,37,55,40,53,48,50,52,44,50,50,38,43,66,40,24,67, 60,71,54,51,60,41,58,20,28,42,53,59,42,31,60,42,58,36,48,53,46,25,53,57,60,35,46,32,26,68,45,20,51, 56,48,25,62,50,54,47,42,55,39,60,44,32,50,34,60,47,70,68,38,47,48,70,51,42,41,35,36,39,23,50,46,44,56,50,39
Brain Pill™ combines the most powerful, clinically proven ingredients on the forefront of brain productivity and memory research. Each of our carefully selected ingredients is potent and effective on its own, but together, our research goal was to create far and away the ultimate synergistic combination for enhancing mental clarity, alertness and overall brain function.
The fish oil can be considered a free sunk cost: I would take it in the absence of an experiment. The empty pill capsules could be used for something else, so we’ll put the 500 at $5. Filling 500 capsules with fish and olive oil will be messy and take an hour. Taking them regularly can be added to my habitual morning routine for vitamin D and the lithium experiment, so that is close to free but we’ll call it an hour over the 250 days. Recording mood/productivity is also free a sunk cost as it’s necessary for the other experiments; but recording dual n-back scores is more expensive: each round is ~2 minutes and one wants >=5, so each block will cost >10 minutes, so 18 tests will be >180 minutes or >3 hours. So >5 hours. Total: 5 + (>5 \times 7.25) = >41.
along with the previous bit of globalization is an important factor: shipping is ridiculously cheap. The most expensive S&H in my modafinil price table is ~$15 (and most are international). To put this in perspective, I remember in the 90s you could easily pay $15 for domestic S&H when you ordered online - but it’s 2013, and the dollar has lost at least half its value, so in real terms, ordering from abroad may be like a quarter of what it used to cost, which makes a big difference to people dipping their toes in and contemplating a small order to try out this ’nootropics thing they’ve heard about.
(I was more than a little nonplussed when the mushroom seller included a little pamphlet educating one about how papaya leaves can cure cancer, and how I’m shortening my life by decades by not eating many raw fruits & vegetables. There were some studies cited, but usually for points disconnected from any actual curing or longevity-inducing results.)
Common issues such as poor sleep during pregnancy and sleep deprivation following the birth can often heighten cravings for stimulants and sugary foods, which may seem like a good option for quick sources of energy, however, these foods can often cause further issues with energy and lead to fatigue and low mood. Eating foods that are high in refined sugar and refined grains such as commercial white bread, pastries, cakes and biscuits, give us an unsustainable source of energy. The brain is a very metabolically active organ; despite it only being 7% of the body’s weight, it can take up to 20% of the body’s metabolic needs (2), meaning that it is very energy hungry. This is why it is important to nourish the brain with foods that are nutrient rich, providing the body the building blocks to produce neurotransmitters, as well as a sustainable source of energy. The best options are fresh, unprocessed foods such as wholegrains (brown bread, brown rice, quinoa, rye and oats), pulses, vegetables, good quality sources of protein (meat, poultry and fish) and healthy fats such as those found in olive oil, coconut oil, avocados and oily fish.
Any consideration of the future of nootropics is directly tied into the future of humanity. As long as work productivity demands continue to soar, there will like be a affiliated rise in the desire to increase brain power. As Vice discusses in a thoughtful article providing several insights into why nootropics are popular, it is not surprising that smart drugs and the nootropic industry are ever-expanding. Vice points out that sci-fi writers once warned of people being overtaken by machines, but instead, human beings are becoming machines, taking on unrealistic work levels. Taking nootropic drugs is akin to loading up on premium fuel in an effort to go faster and do better.
The chemical Huperzine-A (Examine.com) is extracted from a moss. It is an acetylcholinesterase inhibitor (instead of forcing out more acetylcholine like the -racetams, it prevents acetylcholine from breaking down). My experience report: One for the null hypothesis files - Huperzine-A did nothing for me. Unlike piracetam or fish oil, after a full bottle (Source Naturals, 120 pills at 200μg each), I noticed no side-effects, no mental improvements of any kind, and no changes in DNB scores from straight Huperzine-A.
(On a side note, I think I understand now why modafinil doesn’t lead to a Beggars in Spain scenario; BiS includes massive IQ and motivation boosts as part of the Sleepless modification. Just adding 8 hours a day doesn’t do the world-changing trick, no more than some researchers living to 90 and others to 60 has lead to the former taking over. If everyone were suddenly granted the ability to never need sleep, many of them would have no idea what to do with the extra 8 or 9 hours and might well be destroyed by the gift; it takes a lot of motivation to make good use of the time, and if one cannot, then it is a curse akin to the stories of immortals who yearn for death - they yearn because life is not a blessing to them, though that is a fact more about them than life.)
Since LLLT was so cheap, seemed safe, was interesting, just trying it would involve minimal effort, and it would be a favor to lostfalco, I decided to try it. I purchased off eBay a $13 48 LED illuminator light IR Infrared Night Vision+Power Supply For CCTV. Auto Power-On Sensor, only turn-on when the surrounding is dark. IR LED wavelength: 850nm. Powered by DC 12V 500mA adaptor. It arrived in 4 days, on 7 September 2013. It fits handily in my palm. My cellphone camera verified it worked and emitted infrared - important because there’s no visible light at all (except in complete darkness I can make out a faint red light), no noise, no apparent heat (it took about 30 minutes before the lens or body warmed up noticeably when I left it on a table). This was good since I worried that there would be heat or noise which made blinding impossible; all I had to do was figure out how to randomly turn the power on and I could run blinded self-experiments with it.
Potassium citrate powder is neither expensive nor cheap: I purchased 453g for $21. The powder is crystalline white, dissolves instantly in water, and largely tasteless (sort of saline & slightly unpleasant). The powder is 37% potassium by weight (the formula is C6H5K3O7) so 453g is actually 167g of potassium, so 80-160 days’ worth depending on dose.
If all of this sounds great to you, get ready to level up your brain to game like a god with GodMode. Unless, you know, you're under 18, pregnant, potentially have any pre-existing medical conditions, are taking any prescription medications, are otherwise ingesting caffeine or taking other stimulants, or you don't want to drop $60 on gamer pills. Then, you know, don't.
Amphetamines are synthetic stimulants and were first created in 1887. These are among the most powerful stimulant-based smart drugs in use and work primarily by targeting dopamine, serotonin and noradrenaline/norepinephrine. Given what you’ve already learned about the dopaminergic effects of modafinil and methylphenidate, you should already be wary of amphetamines’ targeting of dopamine. Hormones and neurotransmitters such as dopamine, serotonin, norepinephrine and histamine are known as monoamines, and amphetamines block their uptake by being taken up instead themselves by monoamine transporters. This leads to higher levels of monoamines in synapses, and consequently to the psychostimulant effects characteristic of drugs like Adderall.
One thing I notice looking at the data is that the red magnesium-free days seem to dominate the upper ranks towards the end, and blues appear mostly at the bottom, although this is a little hard to see because good days in general start to become sparse towards the end. Now, why would days start to be worse towards the end, and magnesium-dose days in particular? The grim surmise is: an accumulating overdose - no immediate acute effect, but the magnesium builds up, dragging down all days, but especially magnesium-dose days. The generally recognized symptoms of hypermagnesemia don’t include effect on mood or cognition, aside from muscle weakness, confusion, and decreased reflexes…poor appetite that does not improve, but it seems plausible that below medically-recognizable levels of distress like hypermagnesemia might still cause mental changes, and I wouldn’t expect any psychological research to have been done on this topic.
Second, users are concerned with the possibility of withdrawal if they stop taking the nootropics. They worry that if they stop taking nootropics they won’t be as smart as when they were taking nootropics, and will need to continue taking them to function. Some users report feeling a slight brain fog when discontinuing nootropics, but that isn’t a sign of regression.