By Job Osazuwa
Renowned neuroscientist and prolife advocate, Professor Philip C. Njemanze, has released his latest research on cerebral lateralization and general intelligence, gender differences in transcranial Doppler.
The study, in his words, evaluated cerebral lateralization during ravens progressive matrices (RPM) paradigm in female and male subjects.
According to the renowned scientist, bilateral simultaneous transcranial Doppler-ultrasound was used to measure mean blood flow velocities (MBFV) in the right and left middle cerebral arteries (MCAs) in 24 subjects (comprising 15 females and nine males.
Njemanze, who is the chairman of the International Institutes of Advanced Research and Training/Chidicon Medical Centre, Owerri, Imo State, explained that the female subjects used a left hemisphere strategy, while males used a right hemisphere strategy to successfully solve RPM tasks.
He stated that the experiment implies that general intelligence is associated with neural systems within one hemisphere that is accessible to a variety of cognitive processes.
“The determinants of human performance have been a subject of intense debate for over a century. Spearman, in 1904, put forward the idea that measures of performance or success in diverse cognitive tests show a pattern of almost universal positive correlation. He postulated the hypothesis of a general intelligence or g factor making some contribution to success in diverse forms of cognitive activity. Subsequently, two contrasting postulates on cortical localization of intelligence were put forward.
“The first proposes that processing of any task receives contribution from a large set of components or information-processing functions. Therefore, any two tasks are likely to share at least some components, giving rise to universal positive correlation. This hypothesis assumes that general ability is diffusely represented on the whole cortex, and injury to any region of the brain produces an intellectual decrement.
“Conversely, the second so-called hierarchic hypothesis postulates that, in the course of evolution, some area of the brain has gained a dominant role in sustaining general intelligence,” he said.
Njemanze noted that recent positron emission tomography studies have shown selective recruitment of lateral prefrontal cortex in one or both hemispheres. He added that studies of cerebral lateralization of intelligence may implicate one hemisphere, or both, if general abilities were diffusely represented.
He said the purpose of the present study was to evaluate cerebral lateralization during RPM tasks in females and males: “Consequently, unilateral representation of general intelligence will cause MBFV changes in ipsilateral MCA during performance of intelligence tasks. More specifically, the present study evaluates MBFV changes in both MCAs during performance of RPM tasks in both female and male subjects.
“Transcranial Doppler scanning was performed by a method similar to that previously described elsewhere, using a bilateral simultaneous. The Doppler signals and a continuous train of flow velocity envelops were obtained at a depth of 50mm from the probe surface with the same gain and power settings for each subject. MBFV was recorded and averaged in 10s segments for each condition. Subjects were instructed to remain mute and motionless, and the probe-to-vessel angle remained constant throughout the data acquisition.
“A sample RPM task was administered in a practice session to eliminate ambiguity in instructions and reduced any possible role of anxiety due to novelty of task. No subject was aware that RPM measured general intelligence. However, all were motivated to solve the tasks to the best of their abilities.
“It has been argued in the past that a right hemisphere competence may be revealed in non-response conditions due to absence of motor activity. The stimuli were designed to lack verbalized features and excluded the possibility of interference from motor activity, by constrained control of subjects’ response, until after each measurement.”
On the results, “the Vandenberg mental rotation tests depicts rotation in three-dimensional space, and typically yields one of the largest established cognitive gender differences favouring males. Furthermore, processing in three dimensions is not a necessary condition for large sex difference on tests of mental rotation.
“Conversely, superior performance by women on task requiring object location memory has challenged the traditional view that men excel on all spatial tasks. The implications of the present findings of gender differential in RPM task could be better understood if a tentative hypothesis is advanced.
“It could be assumed that general intelligence is related to other lateralized hemispheric cognitive functions including some visuospatial skills. The finding that male subjects used a right hemisphere strategy may well explain the observation in numerous reports that the average level of spatial talents usually requiring general intelligence is higher in male subjects than female. This may suggest that, in males, ipsilateral right hemisphere localization of general intelligence facilitates visuospatial problem-solving.
“On the other hand, in females, transcallosal pathways are implicated in left hemisphere strategy of visuospatial processing. It is plausible that reported gender-related hemispheric advantage is dependent on whether task processing strategies implicate either the intra-hemispheric or transcallosal pathways. Studies in commissurotomy patients might provide further insights on the implication of this model.
“The finding of bi-hemispheric activation with wrong answer may suggest that, increasing level of task difficulty is associated with diverse pattern of neural activation due to broad sampling of all major cognitive functions. It could be postulated that, successful RPM problem-solving employs a discrete knowledge strategy (DKS), that selects neural pathways represented in one hemisphere, while unsuccessful outcome implicates a non-discrete knowledge strategy.
He continued: “RPM paradigm could be viewed as a working memory task. Others have argued that the necessity of keeping several conceptual formulations in mind during the task. The postulates derived from the results of the present study are not aimed at resolving the outstanding issues in intelligence research, but is an attempt to further expand the scope of the discussion raised by results of prior studies.
“It may appear simplistic to measure intelligence based on the RPM task, however, it is worthy to note, that even by this singular test, both cerebral lateralization for intelligence and gender differences were observed.
“The present work suggests that TCD would be useful in the study of the diverse issues involved in intelligence research. TCD has high sensitivity, which is powered to reveal subtle mental performance changes; and capability to reveal the underlying processes that lead to these performance changes.”