The corticotropin-releasing factor (CRF) system is a major coordinator of endocrine, autonomic, and behavioral responses to stress. Altered CRF levels in cerebrospinal fluid and cerebral cortex tissues have been linked with cognitive impairment in Alzheimer’s disease patients. Moreover, decreased amygdala CRF-binding protein messenger RNA was found in postmortem tissue from male bipolar and schizophrenic subjects.
Several components of the dopamine system are thought to play a crucial role in the modulation of various aspects of learning and memory processes. Moreover, dopaminergic dysfunctions, possibly coming from genetic factors, have been associated with cognitive abnormalities in schizophrenia, attention-deficit/hyperactivity disorder, Alzheimer’s disease, Parkinson’s disease, and addiction.
The dopamine transporter (DAT) which transports released neurotransmitter into presynaptic terminals is a major determinant of the intensity and duration of the dopaminergic signal, especially at the level of substantia nigra, ventral tegmental area, and projection areas of the basal ganglia.
Disrupted in schizophrenia 1 (DISC1) is a leading candidate schizophrenia susceptibility gene. Human variants of the gene for proline dehydrogenase (PRODH) have also been associated with increased susceptibility to schizophrenia.
Neuregulin 1 (NRG1) is another gene that has been associated with increased risk for schizophrenia. The neuregulins compose a family of growth and differentiation factors whose effects are mediated via four neuregulin (NRG1-4) genes that bind to the ErbB family of tyrosine kinase transmembrane receptors (ErbB1-4). Centrally, NRG1 is expressed in many regions such as the prefrontal cortex, hippocampus, cerebellum, and substantia nigra in both humans and rodents.
Oxytocin (OT) and Vasopressin (AVP) are closely related nonapeptides that are involved in the neural processing of olfactory cues and social memory. The AVP endogenous system is composed of two central brain receptors, namely Vla receptor (VIal) and VIb receptor (VIbR).
Intelligence is a very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings- “catching on,” “making sense” of things, or “figuring out” what to do.
In practice, intelligence is usually assessed using psychometric (1Q-type) tests, of which there are now hundreds. Scores on these different tests tend to have positive correla-tions, despite a huge variety in the mental demands of the tests.
In children ages 2 to 4, the heritability of mental ability tends to be relatively low, whereas shared environmental estimates explain 61% to 65% of the variance. Parental socioeconomic status (SES) and disorganization in the home mediate some of the shared environmental effect, but most of the shared environmental effects on infant 1Q are still unexplained.
The importance of genetic effects increases from infancy to childhood as demonstrated in longitudinal analyses of twin data from different research groups. At the age of 7, about 47% of the variance in intelligence is due to genetic variance, whereas at the ages of 11 to 12, 60% to 70% of the variance is due to genetic variance.
It has been shown that, although the impact of genetic factors increases with increasing age, the genetic factors remain the same across ages. In other words, the increasing heritability is not explained by emerging effects of a new set of genes coming into play at different ages in childhood. Instead, the effects of the same set of genes become larger with increasing age (“genetic amplification”).
Orienting involves aligning attention with a source of sensory signals. This may be overt as in eye movements or may occur covertly without any movement. The orienting system for visual events has been associated with posterior brain areas including the superior parietal lobule and temporal parietal junction and, in addition, the frontal eye fields. Orienting can be manipulated by presenting a cue indicating where in space a person should attend, thereby directing attention to the cued location.
The superior parietal lobule in humans is closely related to the lateral intraparietal area in monkeys, which is known to produce eye movements. When a target occurs at an uncued location and attention has to be disengaged and moved to a new location, there is activity in the temporal parietal junction. Lesions of the parietal lobule and superior temporal lobe have been consistently related to difficulties in orienting.
Our fMRI-based imaging genetic associations with activation in the anterior cingulate gyrus seem, at face level, generally consistent with the known role of DRD4 and MAOA in brain function. This is mainly because these genes have known roles in dopamine signaling and because the ACC is known as a region rich in dopamine receptors and afferent inputs.
Source : The Genetics of Cognitive Neuroscience by Terry E. Goldberg (Editor), Daniel R. Weinberger (Editor)
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