Neural adaptability: a biological determinant of behavioral intelligence

One Tap at a Time: Correlating Sensorimotor Synchronization with Brain Signatures of Temporal Processing

The ability to integrate our perceptions across sensory modalities and across time, to execute and coordinate movements, and to adapt to a changing environment rests on temporal processing. Timing is essential for basic daily tasks, such as walking, social interaction, speech and language comprehension, and attention. Impaired temporal processing may contribute to various disorders, from attention-deficit hyperactivity disorder and schizophrenia to Parkinson’s disease and dementia. The foundational importance of timing ability has yet to be fully understood; and popular tasks used to investigate behavioral timing ability, such as sensorimotor synchronization (SMS), engage a variety of processes in addition to the neural processing of time. The present study utilizes SMS in conjunction with a separate passive listening task that manipulates temporal expectancy while recording electroencephalographic data. Participants display a larger N1-P2 evoked potential complex to unexpected beats relative to temporally predictable beats, a differential we call the timing response index (TRI). The TRI correlates with performance on the SMS task: better synchronizers show a larger brain response to unexpected beats. The TRI, derived from the perceptually driven N1-P2 complex, disentangles the perceptual and motor components inherent in SMS and thus may serve as a neural marker of a more general temporal processing.

Vigilance Performance: A Review of Electrodermal Predictors

A detailed analysis of electrodermal predictors, used in vigilance studies, suggests that slow habituators display a high over-all level of performance, regardless of task demands and modality. A difference in cautiousness of responding is not involved in this superiority. The evidence that fast habituators exhibit greater performance decrements with time is somewhat less strong. Electrodermal lability, in the sense of spontaneous activity, appeared to be useless as a predictor of over-all vigilant efficiency. The relationship between rate of habituation and performance can be explained in terms of differential allocation of information-processing capacity, although explanations in terms of arousal have also been offered. Speed of habituation has also been linked to intelligence. If in further research it can be shown that the predictive capacity of speed of habituation also applies to more complex, real-world tasks, a practical consequence may be to employ slow habituators in monitoring tasks.

Culture-Fair Cognitive Ability Assessment

Valid assessment with diverse populations requires tools that are not influenced by cultural elements. This study investigated the relationships between culture, information processing efficiency, and general cognitive capacities in samples of Caucasian and Mexican American college students. Consistent with the neural efficiency hypothesis, pupillary responses (indexing mental effort) and detection accuracy scores on a visual backward-masking task were both significantly related to the Wechsler Adult Intelligence Scale-Revised (WAIS-R) Full Scale scores. These measures of information processing efficiency were similar in the two groups. However, they were related only to Caucasian American, but not to a comparable sample of Mexican American, students’ WAIS-R scores. Therefore, the differential validity in prediction suggests that the WAIS-R test may contain cultural influences that reduce the validity of the WAIS-R as a measure of cognitive ability for Mexican American students. Information processing and psychophysiological approaches may be helpful in developing culture-fair cognitive ability measures.

Resting-state sensorimotor rhythm (SMR) power predicts the ability to up-regulate SMR in an EEG-instrumental conditioning paradigm

OBJECTIVE

Instrumental conditioning of EEG activity (EEG-IC) is a promising method for improvement and rehabilitation of cognitive functions. However, it has been found that even healthy adults are not always able to learn how to regulate their brain activity during EEG-IC. In the present study, the role of a neurophysiological predictor of EEG-IC learning performance, the resting-state power of sensorimotor rhythm (rs-SMR, 12-15Hz), was investigated.

METHODS

Eyes-open and eyes-closed rs-SMR power was assessed before N=28 healthy adults underwent 10 training sessions of instrumental SMR conditioning (ISC), in which participants should learn to voluntarily increase their SMR power by means of audio-visual feedback. A control group of N=19 participants received gamma (40-43Hz) or sham EEG-IC.

RESULTS

N=19 of the ISC participants could be classified as "responders" as they were able to increase SMR power during training sessions, while N=9 participants ("non-responders") were not able to increase SMR power. Rs-SMR power in responders before start of ISC was higher in widespread parieto-occipital areas than in non-responders. A discriminant analysis indicated that eyes-open rs-SMR power in a central brain region specifically predicted later ISC performance, but not an increase of SMR in the control group.

CONCLUSIONS

Together, these findings indicate that rs-SMR power is a specific and easy-to-measure predictor of later ISC learning performance.

SIGNIFICANCE

The assessment of factors that influence the ability to regulate brain activity is of high relevance, as it could be used to avoid potentially frustrating and expensive EEG-IC training sessions for participants who have a low chance of success.

Exploring the neural dynamics underpinning individual differences in sentence comprehension

This study used functional magnetic resonance imaging to investigate individual differences in the neural underpinnings of sentence comprehension, with a focus on neural adaptability (dynamic configuration of neural networks with changing task demands). Twenty-seven undergraduates, with varying working memory capacities and vocabularies, read sentences that were either syntactically simple or complex under conditions of varying extrinsic working memory demands (sentences alone or preceded by to-be-remembered words or nonwords). All readers showed greater neural adaptability when extrinsic working memory demands were low, suggesting that adaptability is related to resource availability. Higher capacity readers showed greater neural adaptability (greater increase in activation with increasing syntactic complexity) across conditions than did lower capacity readers. Higher capacity readers also showed better maintenance of or increase in synchronization of activation between brain regions as tasks became more demanding. Larger vocabulary was associated with more efficient use of cortical resources (reduced activation in frontal regions) in all conditions but was not associated with greater neural adaptability or synchronization. The distinct characterizations of verbal working memory capacity and vocabulary suggest that dynamic facets of brain function such as adaptability and synchronization may underlie individual differences in more general information processing abilities, whereas neural efficiency may more specifically reflect individual differences in language experience.

The nature of the black–white difference on various psychometric tests: Spearman's hypothesis

Although the black and white populations in the United States differ, on average, by about one standard deviation (equivalent to 15 IQ points) on current IQ tests, they differ by various amounts on different tests. The present study examines the nature of the highly variable black–white difference across diverse tests and indicates the major systematic source of this between-population variation, namely, Spearman's g. Charles Spearman originally suggested in 1927 that the varying magnitude of the mean difference between black and white populations on a variety of mental tests is directly related to the size of the test's loading on g, the general factor common to all complex tests of mental ability. Eleven large-scale studies, each comprising anywhere from 6 to 13 diverse tests, show a significant and substantial correlation between tests' g loadings and the mean black–white difference (expressed in standard score units) on the various tests. Hence, in accord with Spearman's hypothesis, the average black–white difference on diverse mental tests may be interpreted as chiefly a difference in g, rather than as a difference in the more specific sources of test score variance associated with any particular informational content, scholastic knowledge, specific acquired skill, or type of test. The results of recent chronometric studies of relatively simple cognitive tasks suggest that the g factor is related, at least in part, to the speed and efficiency of certain basic information-processing capacities. The consistent relationship of these processing variables to g and to Spearman's hypothesis suggests the hypothesis that the differences between black and white populations in the rate of information processing may account for a part of the average black–white difference on standard IQ tests and their educational and occupational correlates.

Timing Performance as a Predictor of Psychometric Intelligence as Measured by Speed and Power Tests

In the present study, the relationship between timing performance and psychometric intelligence as measured by a speed and a power test of intelligence was examined. For this purpose performance on the Zahlen-Verbindungs-Test (ZVT), the Wiener Matrizen-Test (WMT), seven psychophysical temporal tasks, and the Hick reaction-time paradigm was obtained in 190 participants. Correlational and principal component analyses suggested a unitary timing mechanism referred to as temporal g. Performance on single temporal tasks and individual factor scores on temporal g were substantially related to both speed and power measures of psychometric intelligence. Temporal g exhibited higher sensitivity to the prediction of performance on the power test than on the speed test. Furthermore, stepwise multiple regression analysis and commonality analysis revealed that timing performance provides a more powerful predictor of psychometric intelligence than traditional reaction-time measures derived from the Hick paradigm. These findings support the notion that the temporal resolution capacity of the brain as assessed with psychophysical temporal tasks reflects an essential property of brain functioning, which is relevant to a wide range of intelligence-related aspects of neural information processing.

Pupillary responses on the visual backward masking task reflect general cognitive ability

Cognitive processing efficiency requires both an ability to attend to task-relevant stimuli with quickness and accuracy, also while filtering distracting or task-irrelevant stimuli. This study investigated cognitive processing efficiency by using pupillary responses as an index of attentional allocation to relevant target and irrelevant masks on a visual backward masking task. The relationship between attentional allocation on this task and general cognitive ability on the scholastic aptitude test (SAT) was examined in college students (n=67). A principle components analysis of the pupillary response waveform isolated a late component that appeared to index the attentional demands associated with processing masks on the backward masking task. This pupillary response index of wasteful resource allocation to the mask accounted for significant variance in SAT scores over and above that accounted for by socio-economic status and target detection accuracy scores. Consistent with the neural efficiency hypothesis, individuals who allocated more resources to processing irrelevant information performed more poorly on cognitive ability tests.

Single-trial analysis of P3 in patients with generalized epilepsy

The latencies and amplitudes of averaged P3, and the latencies, amplitudes and frequency components of single EEG responses to target tones were analyzed in 9 control subjects (CS group), 6 epileptics whose mean IQ was 100 (EP group) and 6 epileptics whose mean IQ was 52 (RE group), using an auditory oddball task. All of the subjects responded to the target tones correctly and there were no differences in the incidence of error in response to the target tones, or in the latencies and amplitudes of the averaged P3 among the three groups. However, the reaction times (RTs) in the RE group were significantly longer than those in the other groups (P < 0.05). Single EEG responses to target tone (single-trial ERPs) were classified into 2 types, those with and those without the P3 component. Type 1 had the P3 component and was observed in 42% of all of the responses in the RE group, significantly less than those in the CS (64%) and EP (61%) groups. The peak latencies of P3 in type 1 were similar among the three groups, but the amplitudes of P3 in type 1 in the RE group were significantly greater than those in the CS and EP groups. RTs in the RE group were significantly longer than those in the other groups, and had no correlation with the P3 latencies of type 1. There was little difference in the results of the frequency analysis among the three groups. These results suggest that all subjects in three groups recognized the target tones correctly, but they did not evaluate every target tone, since the incidence of P3 was almost 60% in the CS and EP groups, and 40% in the RE group. The characteristics of cognition and evaluation in three groups were the same, but the decrease in incidence of evaluation and the dissociation between the cognition and the response execution might be caused by impairment of the subject-environment contact mechanism, which resulted in the decrement of IQ in the RE group.

Neuroscience and human intelligence differences

Research into the biological bases of human intelligence differences is surveyed. Work on brain event-related potentials (ERPs) suggests that people with high IQ test scores: (1) show faster responses in some test conditions; (2) have ERP waveforms that can be distinguished from those of people with lower IQs; and (3) might have less variability in their ERPs. People with higher psychometric intelligence have, on average, larger brains, and possibly faster neural conduction speed. A few small functional brain-scanning studies suggest that, in healthy individuals, people who are of higher IQ have lower cerebral metabolic rates during mentally active conditions. This has led to the speculation that brighter people have more efficient brains. Despite some well-replicated findings in the search for the 'biology of human intelligence' there is a dearth of explanatory accounts to link cognitive performance differences with variance in brain mechanisms.

Event-related potential (ERP) correlates of performance of intelligence tests

Any relationship between measures of cognitive function and brain electrical activity would be of considerable importance in the objective assessment of patients suspected of intellectual impairment. In healthy subjects, we have found a strong correlation between the event-related potentials evoked by a digit probe identification task and scores on intelligence tests (WAIS). Responses from subjects with higher performance on IQ tests are significantly 'more negative' than those from subjects with lower IQ. The characteristics of these IQ-dependent electrophysiological features suggest that they may be related to the subject's ability to focus on a task.

Verbal fluency and positron emission tomographic mapping of regional cerebral glucose metabolism

Impairment in verbal fluency (VF) has been a consistently reported clinical feature of focal cerebral deficits in frontal and temporal regions. More recent behavioral activation studies with healthy control subjects using positron emission tomography (PET), however, have noted a negative correlation between performance on verbal fluency tasks and regional cortical activity. To see if this negative relationship extends to steady-state non-activation PET measures, thirty-three healthy adults were given a VF task within a day of their 18F-2-fluoro-2-deoxy-D-glucose PET scan. VF was found to correlate positively with left temporal cortical region metabolic activity but to correlate negatively with right and left frontal activity. VF was not correlated significantly with right temporal cortical metabolic activity. Some previous studies with normals using behavioral activation paradigms and PET have reported negative correlations between metabolic activity and cognitive performance similar to that reported here. An explanation for the disparate relationships that were observed between frontal and temporal brain areas and VF might be found in the mediation of different task demands by these separate locations, i.e., task planning and/or initiation by frontal regions and verbal memory by the left temporal area.

Parameters of the event-related potential are related to functioning in the mentally retarded

Event-related potentials were measured in 39 institutionalized profoundly and severely retarded clients divided into two groups: clients assigned to sheltered workshop (WS); and clients, residentially matched, but not assigned to workshop (NSW). Since the groups differed in intelligence (p less than 0.01) the ERP was evaluated by analysis of covariance with IQ as the covariate. The WS group had significantly shorter latency of components reflecting initial registration (P1) and channeling (N1) of sensory input and significantly greater amplitude of indices of enhanced perception (P2) and cognitive elaboration (N2). The WS group had significantly more complex waves than the NWS group. A modest (r=0.31, p less than 0.05) relationship between P2 and IQ was observed. Multiple correlations of composite measures of the ERP with IQ were not significant but higher in the NWS than WS group. The possibilities that the ERP be used as a supplemental metric for functional evaluation or that the workshop experience might stimulate central nervous system plasticity were discussed.