The brain's main memory site is the hippocampus. The hippocampus, part of the brain's limbic system, is located in the temporal lobe on the side of the brain. This brain region plays a crucial role in storing information that needs to be kept active for a short amount of time and information that needs to be available for recall over a few days. The area is also involved in transforming short-term memories into long-term memories in the outer layer of the cerebral cortex. Drugs that have received special attention for their adverse effects on memory include statins, barbiturates, benzodiazepines, imidazopyridines and L-dopa.
Statins
HMG-CoA reductase inhibitors, or statins, constitute a class of drugs that lower low-densitity lipoprotein by inhibiting the enzyme HMG-CoA reductase, which is crucial to cholesterol synthesis. Inhibiting this enzyme also gives rise to an increased number of cholesterol receptors, which help to clear the blood of cholesterol. A low blood concentration of bad cholesterol helps prevent strokes and heart attacks and may extend longevity.
According to a study published in the November 2000 issue of "Lancet," statins may cause short-term memory loss and dementia. The exact mechanism is not known.
Barbiturates
Barbiturates are a class of sedative drugs that can decrease symptoms of anxiety, prevent muscle and brain convulsions and induce anesthesia. Prior to the 1960s, barbiturates were frequently used as anti-anxiety drugs or sleep medications. They are now primarily used to prevent seizures, to relieve pain, to induce artificial coma and to act as anesthesia prior to surgery. High doses of barbiturates are used in capital punishment by lethal injection and in active euthanasia.
Barbiturates bind to the same receptor as the naturally occurring inhibitory neurotransmitter GABA. GABA plays an important role in regulating the excitability of the brain and preventing seizures. By binding to this receptor, barbiturates increase the potency of GABA. According to a study published in the November 2002 issue of "The Journal of Neuroscience," barbiturates also inhibit one of the receptors for the excitatory neurotransmitter glutamate.
Barbiturates cause short-term memory loss and impaired cognitive function even at rather low doses. At higher doses they cause loss of consciousness.
Benzodiazepines
Benzodiazepines, which include the popular drugs Xanax and Valium, belong to a class of neuron inhibitory drugs frequently prescribed for alcohol withdrawal, muscle convulsions, muscle tremors, insomnia and anxiety.
Like barbiturates, benzodiazepines bind to the GABA receptor but their mechanism of action is different. Barbiturates prolong the opening of the chloride ion channel at this receptor, whereas benzodiazepines cause more frequent openings. Both mechanisms of action enhance the effect of GABA.
According to a study published in the March 2002 issue of "Consciousness and Cognition," benzodiazepines may cause working memory and short-term memory loss by limiting the complexity of information that is actively available for decision-making and preventing new neural connections in the hippocampus from forming.
Imidazopyridines
Imidazopyridines constitute a class of drugs that include zolpidem--also known as Ambien--alpidem, necopidem and saripidem. Although drugs in this class are chemically unrelated to the benzodiazepines, they have similar effects. They also slow down neuron excitability by binding to GABA receptors. The drugs are more commonly prescribed for insomnia than their effect-related cousins.
According to a report in the February 2007 issue of "Clinical Toxicology," Ambien, the most frequently prescribed drug in this class, can trigger memory loss and other forms of cognitive impairment.
L-Dopa
L-dopa is a dopamine precursor commonly prescribed for Parkinson's disease. Parkinson's disease is a progressive movement disorder that leads to a lack of muscle coordination and difficulties initiating movement. The main trigger of these symptoms is a radical drop in the brain's level of the neurotransmitter dopamine. L-dopa is a naturally occurring drug that is synthesized from the protein building block L-tyrosine and is also the precursor of the stress chemicals adrenaline and noradrenaline. In Parkinson's patients, L-dopa can take the edge of the symptoms.
Parkinson's disease is not itself associated with cognitive degeneration but L-dopa sometimes produce cognitive impairment and learning disabilities, according to a study published in the October 2006 issue of "Neuropsychologia."
References
- "Lancet"; Statins and the Risk of Dementia; H. Jick, et al.; November 2000
- "The Journal of Neuroscience"; Barbiturates Induce Mitochondrial Depolarization and Potentiate Excitotoxic Neuronal Death; Christopher M. Anderson, et al.; November 2002
- "Consciousness and Cognition"; Effects of the Benzodiazepine Lorazepam on Monitoring and Control Processes in Semantic Memory; Marilyne Massin-Krauss, et al.; March 2002
- "Clinical Toxicology"; Compulsive Activity and Anterograde Amnesia after Zolpidem Use; Tsai, et al.; February 2007
- "Neuropsychologia"; L-dopa Impairs Learning, but Spares Generalization, in Parkinson's Disease; Daphna Shohamy, et al.; October 2006
