Tag Archives: Cognition

Transcranial direct current stimulation decreases performance on intelligence test

7 May

The other day, I linked to a popular account of this story. Here is the abstract for the original paper:

Transcranial direct current stimulation (tDCS) modulates excitability of motor cortex. However, there is conflicting evidence about the efficacy of this non-invasive brain stimulation modality to modulate performance on cognitive tasks. Previous work has tested the effect of tDCS on specific facets of cognition and executive processing. However, no randomized, double-blind, sham-controlled study has looked at the effects of tDCS on a comprehensive battery of cognitive processes. The objective of this study was to test if tDCS had an effect on performance on a comprehensive assay of cognitive processes, a standardized intelligence quotient (IQ) test. The study consisted of two substudies and followed a double-blind, between-subjects, sham-controlled design. In total, 41 healthy adult participants completed the Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV) as a baseline measure. At least one week later, participants in substudy 1 received either bilateral tDCS (anodes over both F4 and F3, cathode over Cz, 2 mA at each anode for 20 min) or active sham tDCS (2 mA for 40 s), and participants in substudy 2 received either right or left tDCS (anode over either F4 or F3, cathode over Cz, 2 mA for 20 min). In both studies, the WAIS-IV was immediately administered following stimulation to assess for performance differences induced by bilateral and unilateral tDCS. Compared to sham stimulation, right, left, and bilateral tDCS reduced improvement between sessions on Full Scale IQ and the Perceptual Reasoning Index. This demonstration that frontal tDCS selectively degraded improvement on specific metrics of the WAIS-IV raises important questions about the often proposed role of tDCS in cognitive enhancement.”

The study design seems strong and suggests that one should think twice before running electric currents through the brain.


tDCS, reason to reserve judgement

6 May

Many of the articles I read on transcranial direct current stimulation follow a similar pattern. The intrepid reporter is strapped with electrodes to the skull and, after reporting a tingling feeling, describes some cognitive benefit from the procedure.

A good piece by Kira Peikoff in The New York Times breaks that pattern and acknowledges the limits of our knowledge about tDCS:

“In January, the journal Brain Stimulation published the largest meta-analysis of tDCS to date. After examining every finding replicated by at least two research groups, leading to 59 analyses, the authors reported that one session of tDCS failed to show any significant benefit for users.”



Freddie Gray and lead

5 May

Here is the story in The Washington Post.

“The house where Freddie Gray’s life changed forever sits at the end of a long line of abandoned rowhouses in one of this city’s poorest neighborhoods. The interior of that North Carey Street house, cluttered with couches and potted plants, is lacquered in a fresh coat of paint that makes the living room glow.

But it wasn’t always this way. When Gray lived here between 1992 and 1996, paint chips flaked off the walls and littered the hardwood floor, according to a 2008 lawsuit filed in Baltimore City Circuit Court. The front window­sills shed white strips of paint.”


“Reports of Gray’s history with lead come at a time when the city and nation are still trying to understand the full ramifications of lead poisoning. Advocates and studies say it can diminish cognitive function, increase aggression and ultimately exacerbate the cycle of poverty that is already exceedingly difficult to break.”



Michael O’Hare, at The Reality Based Community, provides some insight:

“The lead angle in Gray’s story should be more featured in the ongoing news coverage, along with the unemployment, social service denial, educational malpractice, and police abuses raining down on his neighborhood. Let me say it again: irreversibly neurologically poisoned.”


Cognitive strengths of older workers

2 May

From The Association for Psychological Science:

“Scientists have long known that our ability to analyze novel problems and reason logically, also known as fluid intelligence, peaks around age 20 and then begins a slow decline. However, two new studies confirm that skills related to crystallized intelligence—made up of a person’s acquired knowledge and experience—appear to peak later in life, often after age 40.”



Video games may not improve cognitive abilities

29 Apr

A paper in Psychological Science suggests that claims about the cognitive enhancing effects of video games may be the result of methodological problems with the research. Here is the abstract:

“The relations between video-game experience and cognitive abilities were examined in the current study. In two experiments, subjects performed a number of working memory, fluid intelligence, and attention-control measures and filled out a questionnaire about their video-game experience. In Experiment 1, an extreme-groups analysis indicated that experienced video-game players outperformed nonplayers on several cognitive-ability measures. However, in Experiments 1 and 2, when analyses examined the full range of subjects at both the task level and the latent-construct level, nearly all of the relations between video-game experience and cognitive abilities were near zero. These results cast doubt on recent claims that playing video games leads to enhanced cognitive abilities. Statistical and methodological issues with prior studies of video-game experience are discussed along with recommendations for future studies.”


“Cognitive Abilities Across the Life Span”

2 Apr

An important paper published in Psychological Science: “When Does Cognitive Functioning Peak? The Asynchronous Rise and Fall of Different Cognitive Abilities Across the Life Span” Here is the abstract (emphasis added):

“Understanding how and when cognitive change occurs over the life span is a prerequisite for understanding normal and abnormal development and aging. Most studies of cognitive change are constrained, however, in their ability to detect subtle, but theoretically informative life-span changes, as they rely on either comparing broad age groups or sparse sampling across the age range. Here, we present convergent evidence from 48,537 online participants and a comprehensive analysis of normative data from standardized IQ and memory tests. Our results reveal considerable heterogeneity in when cognitive abilities peak: Some abilities peak and begin to decline around high school graduation; some abilities plateau in early adulthood, beginning to decline in subjects’ 30s; and still others do not peak until subjects reach their 40s or later. These findings motivate a nuanced theory of maturation and age-related decline, in which multiple, dissociable factors differentially affect different domains of cognition.”

Definitely look at Figure 1 in the pdf.

Walnut consumption and cognitive function

6 Mar

There is a folk belief that eating walnuts improves memory. Here is a study published in The Journal of Nutrition, Health, and Aging offering evidence for this claim.

“Abstract: Objective: To examine the association between walnut consumption and measures of cognitive
function in the US population. Design: Nationally representative cross sectional study using 24 hour dietary recalls of intakes to assess walnut and other nut consumption as compared to the group reporting no nut consumption. Setting: 1988-1994 and 1999-2002 rounds of the National Health and Nutrition Examination Survey (NHANES).

Population: Representative weighted sample of US adults 20 to 90 years of age. Main Outcome Measure: The Neurobehavioral Evaluation System 2 (NES2), consisting of simple reaction time SRTT), symbol digit substitution (SDST), the single digit learning (SDLT), Story Recall (SRT) and digit symbol substitution (DSST) tests. Results: Adults 20-59 years old reporting walnut consumption of an average) of 10.3 g/d required 16.4ms less time to respond on the SRTT, P=0.03, and 0.39s less for the SDST, P=0.01 SDLT scores were also significantly lower by 2.38s (P=0.05). Similar results were obtained when tertiles of walnut consumption were examined in trend analyses. Significantly better outcomes were noted in all cognitive test scores among those with higher walnut consumption (P < 0.01). Among adults 60 years and older, walnut consumers averaged 13.1 g/d, scored 7.1 percentile points higher, P=0.03 on the SRT and 7.3 percentile points higher on the DSST, P=0.05. Here also trend analyses indicate significant improvements in all cognitive test scores (P < 0.01) except for SRTT (P = 0.06) in the fully adjusted models.

Conclusion: These significant, positive associations between walnut consumption and cognitive functions among all adults, regardless of age, gender or ethnicity suggest that daily walnut intake may be a simple beneficial dietary behavior.”

This study has some clear limitations. It is correlational not experimental and cannot demonstrate a cause and effect relationship between walnuts and cognitive function. In addition, it is based on self-report walnut consumption, a measure that might not be accurate.

You can find Seth Roberts posts on walnuts here.



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