Earliest memories

I found a rather old-ish paper which attempts to settle a curiosity regarding human memory: how far back can we remember?

MacDonald et al. (2000) got 96 participants to fill a 15-minute questionnaire about their demographics and their earliest memories. The New Zealand subjects were in their early twenties, a third of Maori descent, a third of European descent and the last third of Asian descent.

The Maori had the earliest memories, some of them as early as before they turned 1 year old, though the mean was 2 years and 8 months. Next came the Europeans with the mean of 3 years and a half, followed by the Asians with the mean of 4 and 9 months. Overall, most memories seem to occur between 3 and 4 years. There was no difference in gender except for the Asian group where the females reported much later memories, around 6 years.

The subjects were also required to indicate the source of the memory as being personal recollection, family story or photographs. About 86% reported it as personal recollection. The authors argue that even without the remaining 14% the results looks the same. I personally would have left those 14% out if they really don’t make a difference, it would have made the results much neater.

There are a few caveats that one must keep in mind with this kind of studies, the questionnaire studies. One of them is the inherent veracity problem: you rely on human honesty because there is no way to check the data for truth. The fact that the memory may be true or false would not matter for this study, but whether is a personal recollection or a family story would matter. So take the results at face value. Besides, human memory is extremely easy to manipulate, therefore some participants may actually believe that they ‘remember’ an event when in fact it was learned much later from relatives. I also have very early memories and while one of them I believe was told ad nauseam by family members at every family gathering so many times that I incorporated it as actual recollection, there are a couple that I couldn’t tell you for the life of me whether I remember them truly or they too have been subjected to family re-reminiscing.

Another issue might be the very small sample sizes with sub-groups. The authors divided their participants in many subgroups (whether they spoke English first, whether they were raised mainly by the mother etc.) that some subgroups ended up having 2 or 3 members, which is not enough to make a statistical judgement. Which also leads me to multiple comparisons adjustments, which should be more visible.

So not exactly the best paper ever written. Nevertheless, it’s an interesting paper in that even if it doesn’t really establish (in my opinion) when do most people have their earliest true memories, it does point to cultural differences in individuals’ earliest recollections. The authors speculate that that may be due to the emphasis put on detailed stories about personal experiences told by the mother in the early years in some cultures (here Maori) versus a lack of these stories in other cultures (here Asian).

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Reference: MacDonald S, Uesiliana K, & Hayne H. (Nov 2000). Cross-cultural and gender differences in childhood amnesia. Memory. 2000 Nov;8(6):365-76. PMID: 11145068, DOI: 10.1080/09658210050156822. ARTICLE | FULLTEXT PDF

By Neuronicus, 28 November 2016

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Can you tickle yourself?

As I said before, with so many science outlets out there, it’s hard to find something new and interesting to cover that hasn’t been covered already. Admittedly, sometimes some new paper comes out that is so funny or interesting that I too fall in line with the rest of them and cover it. But, most of the time, I try to bring you something that you won’t find it reported by other science journalists. So, I’m sacrificing the novelty for originality by choosing something from my absolutely huge article folder (about 20 000 papers).

And here is the gem for today, titled enticingly “Why can’t you tickle yourself?”. Blakemore, Wolpert & Frith (2000) review several papers on the subject, including some of their own, and arrive to the conclusion that the reason you can’t tickle yourself is because you expect it. Let me explain: when you do a movement that results in a sensation, you have a pretty accurate expectation of how that’s going to feel. This expectation then dampens the sensation, a process probably evolved to let you focus on more relevant things in the environment that on what you’re doing o yourself (don’t let your mind go all dirty now, ok?).

Mechanistically speaking, it goes like this: when you move your arm to tickle your foot, a copy of the motor command you gave to the arm (the authors call this “efference copy”) goes to a ‘predictor’ region of the brain (the authors believe this is the cerebellum) that generates an expectation (See Fig. 1). Once the movement has been completed, the actual sensation is compared to the expected one. If there is a discrepancy, you get tickled, if not, not so much. But, you might say, even when someone else is going to tickle me I have a pretty good idea what to expect, so where’s the discrepancy? Why do I still get tickled when I expect it? Because you can’t fool your brain that easily. The brain then says; “Alright, alright, we expect tickling. But do tell me this, where is that motor command? Hm? I didn’t get any!” So here is your discrepancy: when someone tickles you, there is the sensation, but no motor command, signals 1 and 2 from the diagram are missing.

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Fig. 1. My take on the tickling mechanism after Blakemore, Wolpert & Frith (2000). Credits. Picture: Sobotta 1909, Diagram: Neuronicus 2016. Data: Blakemore, Wolpert & Frith (2002). Overall: Public Domain

Likewise, when someone tickles you with your own hand, there is an attenuation of sensation, but is not completely disappeared, because there is some registration in the brain regarding the movement of your own arm, even if it was not a motor command initiated by you. So you get tickled just a little bit. The brain is no fool: is aware of who had done what and with whose hands (your dirty mind thought that, I didn’t say it!) .

This mechanism of comparing sensation with movement of self and others appears to be impaired in schizophrenia. So when these patients say that “I hear some voices and I can’t shut them up” or ” My hand moved of its own accord, I had no control over it”, it may be that they are not aware of initiating those movements, the self-monitoring mechanism is all wacky. Supporting this hypothesis, the authors conducted an fMRI experiment (Reference 2) where they showed that that the somatosensory and the anterior cingulate cortices show reduced activation when attempting to self-tickle as opposed to being tickled by the experimenter (please, stop that line of thinking…). Correspondingly, the behavioral portion of the experiment showed that the schizophrenics can tickle themselves. Go figure!

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Reference 1: Blakemore SJ, Wolpert D, & Frith C (3 Aug 2000). Why can’t you tickle yourself? Neuroreport, 11(11):R11-6. PMID: 10943682. ARTICLE FULLTEXT

Reference 2: Blakemore SJ, Smith J, Steel R, Johnstone CE, & Frith CD (Sep 2000, Epub 17 October 2000). The perception of self-produced sensory stimuli in patients with auditory hallucinations and passivity experiences: evidence for a breakdown in self-monitoring. Psychological Medicine, 30(5):1131-1139. PMID: 12027049. ARTICLE

By Neuronicus, 7 August 2016

Not all children diagnosed with ADHD have attention deficits

ADHD

Given the alarming increase in the diagnosis of attention deficit/hyperactivity disorder (ADHD) over the last 20 years, I thought pertinent to feature today an older paper, from the year 2000.

Dopamine, one of the chemicals that the neurons use to communicate, has been heavily implicated in ADHD. So heavily in fact that Ritalin, the main drug used for the treatment of ADHD, has its main effects by boosting the amount of dopamine in the brain.

Swanson et al. (2000) reasoned that people with a particular genetic abnormality that makes their dopamine receptors work less optimally may have more chances to have ADHD. The specialist reader may want to know that the genetic abnormality in question refers to a 7-repeat allele of a 48-bp variable number of tandem repeats in exon 3 of the dopamine receptor number 4 located on chromosome 11, whose expression results in a weaker dopamine receptor. We’ll call it DRD4,7-present as opposed to DRD4,7-absent (i.e. people without this genetic abnormality).

They had access to 96 children diagnosed with ADHD after the diagnostic criteria of DSM-IV and 48 matched controls (children of the same gender, age, school affiliation, socio-economic status etc. but without ADHD). About half of the children diagnosed with ADHD had the DRD4,7-present.

The authors tested the children on 3 tasks:

(i) a color-word task to probe the executive function network linked to anterior cingulate brain regions and to conflict resolution;
(ii) a cued-detection task to probe the orienting and alerting networks linked to posterior parietal and frontal brain regions and to shifting and maintenance of attention; and
(iii) a go-change task to probe the alerting network (and the ability to initiate a series of rapid response in a choice reaction time task), as well as the executive network (and the ability to inhibit a response and re-engage to make another response) (p. 4756).

Invalidating the authors’ hypothesis, the results showed that the controls and the DRD4,7-present had similar performance at these tasks, in contrast to the DRD4,7-absent who showed “clear abnormalities in performance on these neuropsychological tests of attention” (p. 4757).

This means two things:
1) Half of the children diagnosed with ADHD did not have an attention deficit.
2) These same children had the DRD4,7-present genetic abnormality, which has been previously linked with novelty seeking and risky behaviors. So it may be just possible that these children do not suffer from ADHD, but “may be easily bored in the absence of highly stimulating conditions, may show delay aversion and choose to avoid waiting, may have a style difference that is adaptive in some situations, and may benefit from high activity levels during childhood” (p. 4758).

Great paper and highly influential. The last author of the article (meaning the chief of the laboratory) is none other that Michael I. Posner, whose attentional networks, models, and tests feature every psychology and neuroscience textbook. If he doesn’t know about attention, then I don’t know who is.

One of the reasons I chose this paper is because it seems to me that a lot of teachers, nurses, social workers, or even pediatricians feel qualified to scare the living life out of parents by suggesting that their unruly child may have ADHD. In deference to most form the above-mentioned professions, the majority of people recognize their limits and tell the concerned parents to have the child tested by a qualified psychologist. And, unfortunately, even that may result in dosing your child with Ritalin needlessly when the child’s propensity toward a sensation-seeking temperament and extravert personality, may instead require a different approach to learning with a higher level of stimulation (after all, the children form the above study had been diagnosed by qualified people using their latest diagnosis manual).

Bottom line: beware of any psychologist or psychiatrist who does not employ a battery of attention tests when diagnosing your child with ADHD.

Reference: Swanson J, Oosterlaan J, Murias M, Schuck S, Flodman P, Spence MA, Wasdell M, Ding Y, Chi HC, Smith M, Mann M, Carlson C, Kennedy JL, Sergeant JA, Leung P, Zhang YP, Sadeh A, Chen C, Whalen CK, Babb KA, Moyzis R, & Posner MI. (25 April 2000). Attention deficit/hyperactivity disorder children with a 7-repeat allele of the dopamine receptor D4 gene have extreme behavior but normal performance on critical neuropsychological tests of attention. Proceedings of the National Academy of Sciences of the United States of America, 97(9):4754-4759. doi: 10.1073/pnas.080070897. Article | FREE PDF

P.S. If you think that “weeell, this research happened 16 years ago, surely something came out of it” then think again. The newer DSM-V’s criteria for diagnosis are likely to cause an increase in the prevalence of diagnosis of ADHD.

By Neuronicus, 26 February 2016