Jeremy R. Gray, Christopher F. Chabris and Todd S. Braver

Elaine Chan

Neural mechanisms of general fluid intelligence

Background InformationThe general intelligence factor (g) is

a construct used to quantify what is common to the scores of all intelligence tests1904: Charles Spearman

Background InformationFluid intelligence (F) – Raymond Cattell

the ability to find meaning in confusion and solve new problems, to draw inferences and understand the relationships of various concepts, independent of acquired knowledge

General fluid intelligence (gF)a major dimension of individual

differences

IntroductionEvidence from cognitive (behavioural)

and anatomical studies suggests that gF should covary with both task performance and neural activity in specific brain systems when specific cognitive demands are presentwith the neural activity mediating the

relation between gF and performance

Cognitively: gF thought to be related to metacognition (knowing about and reflecting upon one’s own ongoing mental processes) and to working memoryEg/the ability to overcome interference that

would otherwise disrupt performance by compromising task goals or information held active in working memory

Anatomically: the neural substrate of gF is thought to include portions of the prefrontal cortex (PFC)No previous studies have correlated gF with

neural function across individuals

Direct investigation of this would help create a mechanistic model of human intelligence, which might in turn suggest ways to enhance gF through behavioural or neurobehavioural interventions.

Hypothesis

Individual differences in gF will be most evident on lure trials, both in terms of task performance and neural activity in areas that are critical for cognitive control.

MethodsAssessed gF in subjects using a standard

measure (Raven’s Advanced Progressive Matrices) administered outside of the MR scanner

Then, used fMRI to measure event-related brain activity as participants performed a challenging computerized three-back taskIndividual differences in gF most pronounced in

behavioural measures when attentional control is required

Target, lure, and non-lure trials

Three-back task

SubjectsOriginally 60 participants (29 male, 31

female)12 excluded due to technical problems,

excessive head movement, or too few trials48 participants used for results

Healthy, right-handed, native English speakers

Aged 18-37 yearsNo history of neurological disorder, current

psychoactive medication, or other factors that would affect the fMRI results

Results – Behavioural dataLure trials were far

more difficult than non-lure trials

Higher gF correlated positively with accuracy on both lure trials and non-lure trials

Results – Neuroimaging dataOn lure trials, gF correlated positively

with the magnitude of event-related activity in the a priori search space (lateral PFC, dorsal anterior cingulate, and lateral cerebellum), as well as across the whole brain (within parietal and temporal cortex)

Discussionlateral PFC, suspected to support reasoning

and novel problem solving ability, does show meaningful neural activity which mediates the relation between ability (gF) and performance on a demanding working-memory taskprovides the first direct support for a major

hypothesis about the neurobiological basis of gF

gF-related differences in brain activity emerged almost exclusively on working memory trials with high interference, as predicted from behavioural evidence showing the importance of attentional control in protecting goals, or other information held actively in mind, from such interference

ConfoundsSome of the identified regions of neural

signalling may not contribute causally to task performance, or may be supporting a different cognitive function than working memoryEg/ inhibition of incorrect responses cued

by familiarity

My OpinionStrengths:

Experiment type gave a high degree of experimental control over individual differences in motivation and other potential confounds

Weaknesses:The results section describing the

neuroimaging data was unclearWould have benefited from more diagrams

and images of the brain areas in question

Future Studies?Sex differences?

Further explore relationships among functional, structural, genetic and cognitive correlates of gF within the same sample

Thank you!References:Gray JR, Chabris CF, Braver TS. (2003)

Neural mechanisms of general fluid intelligence. Nat Neurosci. 6(3):316-22.

Any Questions?