The most common kinds of memory loss are loss of working memory and loss of short-term memory. Working memory loss, in many cases, stems from damage to the prefrontal cortex. Short-term memory loss is primarily due to damage to or plaque formation in the hippocampus, one of the brain's main memory centers. Working memory loss can be a result of conditions such as dementia, attention-deficit hyperactivity disorder, strokes in the prefrontal cortex and depression; while short-term memory loss typically occurs with conditions such as Alzheimer's disease, strokes in the temporal lobe, depression and schizophrenia.
Acetylcholine Stimulants
Alzheimer's disease is correlated with a break down of the neurotransmitter acetylcholine and heightened levels of the neurotransmitter glutamate. A radical increase in the brain levels of glutamate leads to neuron death. One group of drugs approved for the treatment of Alzheimer's disease acts by regulating the brain's levels of acetyalcholine, which slows down the progression of Alzheimer's. This class of drugs includes tacrine, donepezil, rivastigmine and galantamine.
Marijuana constitutes a more controversial acetylcholine stimulant. Using computational modeling, a Scripps Research team showed that the active ingredient in marijuana called delta-9-tetrahydrocannabinol, or THC, prevents the enzymatic break-down of acetylcholine. The findings were published in the October 2006 issue of "Molecular Pharmaceutics." However, a Canadian research team was unable to confirm the theory that THC may prevent or reverse Alzheimer's. The study, which was published in the May 2010 issue of "Current Alzheimer Research," used mice with the human genetic mutations associated with Alzheimer's disease to test the effectiveness of the chemical.
Glutamate Down Regulators
A newer class of drugs regulates the brain's levels of glutamate, thus preventing the death of neurons. The only FDA-approved drug in this class is memantine. The drug is prescribed for Alzheimer's and other forms of damage to the hippocampus, including stroke and trauma.
Memantine has met with some controversy. According to a report published in the January 2008 online issue of "Journal of Alzheimer's Disease," the drug doesn't have any significant effect on glutamate. At lower dosages, the drug functions as an acetylcholine stimulant just like the older class of drugs typically prescribed for Alzheimer's, the researchers report.
Selective Serotonin Reuptake Inhibitors
Selective serotonin reuptake inhibitors are frequently prescribed for major depression. The serotonin reuptake inhibitor escitalopram, or Lexapro, is also commonly prescribed for generalized anxiety disorder. Recent experiments, however, show that this group of drugs also stimulates the generation of new neurons in areas of the brain affected by memory loss. An Iowa research team tested the effects of escitalopram on memory recovery after a stroke. The study, which was published in the February 2010 issue of "Archives of General Psychiatry," found that stroke patients who were given a small dose of escitalopram scored better on memory tests after only 12 weeks of treatment compared to controls.
Dopamine Reuptake Inhibitors
Dopamine reuptake inhibitors, such as methylphenidate, are commonly prescribed drugs for attention deficit hyperactivity disorder, or ADHD. People with ADHD have abnormal levels of dopamine. Insufficient amounts of dopamine in the brain typically lead to a smaller reward feeling when completing a task and working and short-term memory deficiencies. Dopamine reuptake inhibitors work by blocking a protein that absorbs dopamine, thus raising the brain's levels of dopamine. Methylphenidate specifically targets areas of the prefrontal cortex associated with working memory and also has some effect on short-term memory, reports a Wisconsin research team in the June 2006 issue of "Biological Psychiatry."
Other drugs commonly prescribed for ADHD, including amphetamine and a stereoisomer, or one side, of amphetamine, raise the brain's levels of dopamine by binding to dopamine receptors in the brain. However, this group of drugs do not specifically target the dopamine receptors in the hippocampus, and therefore has little effect on short-term memory.
References
- "Molecular Pharmaceutics"; A Molecular Link between the Active Component of Marijuana and Alzheimer's Disease Pathology; Lisa M. Eubanks, et al.; October 2006
- "Current Alzheimer Research"; "Effect of Synthetic Cannabinoid HU210 on Memory Deficits and Neuropathology in Alzheimer's Disease Mouse Model"; B. Chen, et al.; May 2010
- "Journal of Alzheimer's Disease"; Memantine Acts as a Cholinergic Stimulant in the Mouse Hippocampus; Benjamin D. Drever, et al.; January 2008
- "Archives of General Psychiatry"; Escitalopram and Enhancement of Cognitive Recovery Following Stroke; Jorge, et al.; February 2010
- "Biological Psychiatry"; Methylphenidate Preferentially Increases Catecholamine Neurotransmission within the Prefrontal Cortex at Low Doses that Enhance Cognitive Function; Craig W. Berridge, et al.; June 2006
