In general, the majority of changes in human intelligence occur at either the onset of development, during the critical period, or during old age (see neuroplasticity).
[1] In general, intelligence is thought to be attributed to both genetic and environmental factors, but the extent to which each plays a key role is highly disputed.
Studies of identical and non-identical twins raised separately and together show a strong correlation between child IQ and socio-economic level of the parents.
[2] The biological basis of intelligence is founded in the degree of connectivity of neurons in the brain and the varying amounts of white and grey matter.
[2] During the critical period, the neuronal pathways are refined based on which synapses are active and receiving transmission.
[6] It refers to a change in neural connectivity as a result of high activation on both sides of a synaptic cleft.
[7] Humans have varying degrees of neuroplasticity due to their genetic makeups, which affects their ability to adapt to conditions in their environments and effectively learn from experiences.
[3] Numerous pharmacological developments have been made to help organize neural circuitry for patients with learning disorders.
The cholinergic and glutamatergic systems in the brain serve an important role in learning, memory, and the developmental organization of neuronal circuitry.
Specifically, glutamatergic drugs may reduce the threshold for LTP, promote more normal dendritic spine morphology, and retain a greater number of useful synaptic connections.
Cholinergic drugs may reconnect the basal forebrain with the cortex and hippocampus, connections that are often disrupted in patients with learning disorders.