Neuroimaging intelligence testing

Neuroimaging intelligence testing concerns the use of neuroimaging techniques to evaluate human intelligence. Neuroimaging technology has advanced such that scientists hope to use neuroimaging increasingly for investigations of brain function related to IQ.'The n-back task is typically thought to require the updating of information in WM, because, for each sequentially presented item, the participant must judge whether it matches the item presented n trials back (where n is prespecified, and usually equals 1, 2, or 3 items).''A lateral prefrontal cortex (LPFC) region's activity was found to predict performance in a high control demand working memory task and also to exhibit high global connectivity. Critically, global connectivity in this LPFC region, involving connections both within and outside the frontoparietal network, showed a highly selective relationship with individual differences in fluid intelligence.' Neuroimaging intelligence testing concerns the use of neuroimaging techniques to evaluate human intelligence. Neuroimaging technology has advanced such that scientists hope to use neuroimaging increasingly for investigations of brain function related to IQ. Traditional IQ tests observe the test-taker's performance in a standardized battery of samples of behavior. The resulting IQ standard score is the subject of much investigation as psychologists check correlations between IQ and other life outcomes. The Wechsler IQ tests for adults and for children have long been regarded as the 'gold standard' in IQ testing. The varying techniques of imaging-based testing search for different signs of intelligence. The types of intelligence analyzed in this review were fluid intelligence (Gf), general intelligence (g), and crystallized intelligence (Gc). Early studies utilized information from patients with brain damage, noticing changes in intelligence scores that correlated to certain regions of the brain. As imaging technology has improved, so has the ability for deeper neuro-analysis. MRI studies have found that the volume of gray matter correlates to intelligence, providing evidence for generalizations made regarding brain/head-size and intelligence. Additionally, PET and fMRI studies have revealed more information regarding the functionality of certain regions of the brain. By recording and interpreting the brain activity of subjects as they complete a variety of tasks, researchers are able to draw connections between the types of task (and thus, the type of intelligence) that calls on particular areas of the brain. This is interesting as knowing how parts of the brain are utilized may reveal more information about the structure and hierarchy used in neural development. It also may provide interesting information regarding the pathways of neural signals as they navigate the nervous system. Image-based testing may allow researchers to discover why certain neurons are connected, if they are indeed aligned in a purposeful manner and consequently, how to repair such pathways when they are damaged. In general, there have been two types of intelligence studies: psychometric and biological. Biological approaches make use of neuroimaging techniques and examine brain function. Psychometrics focuses on mental abilities. Ian Deary and associates suggest that a greater overlap of these techniques will reveal new findings. Psychometrics is a field of study specifically dedicated to psychological measurement and involves two main tasks: (i) constructing instruments and procedures for measurement; and (ii) the development and refinement of theoretical approaches to measurement. Brain-based intelligence tests are concerned with both of these aspects. Modern techniques have evolved to focus on a few biological characteristics: Brain ERPs, brain size, and speed of neural conduction. Various instruments have been employed to measure these things. Brain ERPs allow for the 'sequencing' of psychologically interesting processing. These event-related potentials are measured brain responses to specific stimuli, such as sensory, cognitive or motor events. ERPs, when compared to 'mental speed,' have shown a negative correlation with IQ. Research with ERPs suggests that high IQ individuals have a faster response time in some test conditions, have distinguishable ERP waveforms that are different than those of people with lower IQs, and may have less variability in their ERPs. The lack of variability suggests that individuals with a high IQ will have good scores in a variety of testing situations. ERPs can be measured using electroencephalography (EEG), which uses electrodes placed on the scalp to measure the electrical activity of the brain. The ERP waveform itself is constructed from the averaged results of many trials (100 or more). The average reduces signal noise from random-brain activity, leaving just the ERP. An advantage of ERPs are that they measure processing between stimulus and response continuously. Having this stream of information makes it possible to see where the brain's electrical activity is being affected by specific stimuli. Using MRI, researchers are able to acquire volumetric measurements of brain size. Some studies have tried to explain the relationship between brain size (meaning volume) and intelligence, specifically in terms of IQ. In general, it has been found that Full Scale IQ and Verbal IQ have a stronger correlation with brain size than Performance IQ. It is thought by some that grey and white matter specifically relate to different IQs (grey matter with Verbal IQ and white matter with Performance IQ), but the results have not been consistent. It has been found that within the cortex, the correlation with IQ was very influenced by the volume of prefrontal grey matter. A 2009 study examined intracerebral volumetric relationships in twins. Making use of high resolution MRI data, they found strong genetic connections correlations between cerebral structures. Specifically, the study suggests that a strong correlation exists between the tissue type or spatial proximity and genes. By examining the differences or lack thereof between the brain size of twin children, the researchers drew conclusions that individuals that share genes (i.e. twins) will show similar physiological brain properties compared to genetically-unrelated individuals. This study provides evidence of the genetic influence of the brain structure and size, which are believed to both influence intelligence in some way.