Retrograde memory loss, or amnesia, is the loss of memories acquired prior to a brain damage. Retrograde memory loss includes loss of memory of facts and events, also known as "declarative memory," and loss of "how-to" memory, also known as "procedural memory." Both types of memory loss can be debilitating, but a loss of procedural memory can interfere with the ability to carry out the simplest everyday tasks, such as tying a shoe or opening a can of tuna.
Damages to Hippocampus
The leading cause of retrograde amnesia is a damage to the hippocampus, an area of the brain crucial to memory, reports Liverpool psychologist Juliet Holdstock in the October 2008 issue of "Hippocampus." When the hippocampus deteriorates, the information stored in this area is lost. The hippocampus is also involved in maintaining long-term memory in the outer layer of the brain called "the cerebral cortex." Without an actively functioning hippocampus, this information eventually disintegrates as well. The diseases and conditions that can impair hippocampal function include carbon monoxide poisoning, temporal lobe strokes, Alzheimer's Disease, Meningitis, Herpes, major depression and psychotic disorders.
Damages to the Parietal Lobe
The parietal lobe is a crucial area of the brain for guiding action. Damages to the parietal lobe from strokes or poisoning can make it difficult for people to control their grip aperture when reaching for objects. This amounts to retrograde loss of procedural memory. In worst case scenarios strokes can cause alien hand syndrome, which results in involuntary reaching and grasping behavior, reports a research team in a July 2007 issue of "Annals of Neurology". When patients also suffer from visual neglect, a condition in which the subject is unaware of things in either the left or right visual field despite having normal visual pathways, she may even be unaware that her hand is touching and reaching for objects.
Damages to Basal Ganglia
The basal ganglia is a group of neurons at the base of the forebrain which plays a crucial role in learning and motor control. Damages to basic ganglia through a stroke or head injury cause retrograde procedural memory loss. Procedural memory involves not only memory of simple tasks such as memories of how to tie your shoe but also memories of how to speak a language and create sentences quickly, reports a research team in the July 2007 issue of "Neuropsychologia." The researchers discovered the close connection between basic ganglia and language skills when they did their research on children with Tourette's syndrome, a neurological disorder that involves basal ganglia. Though the study participants had uncontrollable movements, tics and exclamations, they processed grammar formation rules and other language procedures faster than normal children.
Marijuana Use
Frequent marijuana use can cause retrograde long-term memory loss, reports Pompeu Fabra neuroscientist Andrés Ozaita in the August 2009 issue of "Nature Neuroscience." Ozaita and his team examined the effects of the psychoactive chemical compound THC on the brain. THC binds to receptors in the hippocampus known as "cannabinoid receptors." This stimulates the so-called GABA pathway, in which GABA neurons release GABA, a chemical that inhibits cell activity and in natural amounts helps to prevent seizures.
Concussion
Formation of long-term memories occur when information is transmitted to the cerebral cortex and the synapses of the neurons in this area are strengthened via a shut-down mechanism signaling to a receptor molecule called "nogo receptor 1", or NgR1, reports Karolinska Institute neuroscientist Lars Olson in the December 2009 issue of "PNAS." Concussions, the most common form of traumatic head injury, can cause damage to this receptor mechanism failing to shut down the gene. This results in a deterioration of recent experiences, which means the information in hippocampus does not get stored in long-term memory.
References
- "Hippocampus"; Two Case Studies Illustrating How Relatively Selective Hippocampal Lesions in Humans Can Have Quite Different Effects on Memory; Holdstock, et al.; vol. 18, 2008
- "Annals of Neurology"; Moving With or Without Will: Functional Neural Correlates of Alien Hand Syndrome; Assal, et al.; July 2007
- "Neuropsychologia"; Speeded processing of grammar and tool knowledge in Tourette's syndrome; Walenski, et al.; July 2007
- "Nature Neuroscience"; Cannabinoid modulation of hippocampal long-term memory is mediated by mTOR signaling; Puighermanal, et al.; August 2009
- "PNAS"; Nogo receptor 1 regulates formation of lasting memories; Karlen, et al.; December 2009
