Source amnesia is the inability to remember where, when or how previously learned information has been acquired, while retaining the factual knowledge. This branch of amnesia is associated with the malfunctioning of one's explicit memory. It is likely that the disconnect between having the knowledge and remembering the context in which the knowledge was acquired is due to a dissociation between semantic and episodic memory – an individual retains the semantic knowledge (the fact), but lacks the episodic knowledge to indicate the context in which the knowledge was gained. Memory representations reflect the encoding processes during acquisition. Different types of acquisition processes (e.g.: reading, thinking, listening) and different types of events (e.g.: newspaper, thoughts, conversation) will produce mental depictions that perceptually differ from one another in the brain, making it harder to retrieve where information was learned when placed in a different context of retrieval. Source monitoring involves a systematic process of slow and deliberate thought of where information was originally learned. Source monitoring can be improved by using more retrieval cues, discovering and noting relations and extended reasoning.
Causes Source amnesia is not a rare phenomenon – everybody experiences it on a near daily basis as, for much of our knowledge, it is important to remember the knowledge itself, rather than its source. However, there are extreme examples of source amnesia caused by a variety of factors.
Frontal lobe damage Individuals with frontal lobe damage have deficits in temporal context memory; source memory can also exhibit deficits in those with frontal lobe damage. It appears that those with frontal lobe damage have difficulties with recency and other temporal judgements (e.g., placing events in the order they occurred), and as such they are unable to properly attribute their knowledge to appropriate sources (i.e., have source amnesia). Those individuals with frontal lobe damage have normal recall of facts, but they make significantly more errors in source memory than control subjects, with these effects becoming apparent as shortly as 5 minutes after the learning experience. Individuals with frontal lobe damage often mistakenly attribute the knowledge they have to some other source (e.g., they read it somewhere, saw it on TV, etc.) but rarely attribute it to having learned it over the course of the experiment. It appears that frontal lobe damage causes a disconnection between semantic and episodic memory – in that the individuals cannot associate the context in which they acquired the knowledge to the knowledge itself.
Age-related Elderly individuals have been shown to exhibit source amnesia. Compared to younger individuals, in experiments where the individuals are presented with obscure or even made up trivia facts, older people remember less information overall in both recall and recognition tasks and they often misattribute the source of their knowledge, at time periods of both long and short delays. This effect is potentially due to the neuronal loss associated with aging occurring mainly in the frontal lobes. It has been previously noticed that frontal lobe damage can cause source amnesia, so the loss of neurons in this area of the brain associated with aging may very well be the cause of the age-related source amnesia seen.
Alzheimer's disease Alzheimer's disease (AD), which is known to be associated with frontal lobe dysfunction, is implicated as a cause of source amnesia. In laboratory conditions, one study found source monitoring to be so poor that the AD participants were correctly performing source memory attributions at approximately chance. This lack of ability to attribute the source of memories is likely related to AD patients' deficits in reality monitoring. Reality monitoring, the process of distinguishing whether information originated from an external or an internal source, relies on judgement processes to examine the qualitative characteristics of the information in order to determine if the information was real or imagined. It appears that it is this process that is experiencing the dysfunction, which causes mild confabulation in some AD patients, as well as being related to the source amnesia experienced in some individuals with AD.
Schizophrenia Schizophrenia is associated with episodic memory deficits often characterized by a confusion of internal stimuli and real events. It appears that individuals with schizophrenia often display failures in monitoring/remembering the source of information, especially for self-generated items – that is, they display source amnesia. This is a stable trait in this disease – one experiment found that over a two-year period, an individual's rate of source attributing errors was maintained, despite fluctuations in medication status and the individual's symptoms. This effect is possibly due to the malformation of associations among aspects of an episode needed for remembering its source; one neuroimaging study found that individuals with schizophrenia had lower activation of areas associated with source memory. Individuals with schizophrenia who display source memory deficits often do so due to reality-monitoring dysfunction, which is a contributing factor towards the hallucinations that characterize the disorder. One study found that schizophrenia patients were not only slower, but also less accurate, at tasks involving reality-monitoring. The hallucinations that characterize schizophrenia are a result of deficit in reality monitoring – they exhibit an inability to differentiate between internally and externally derived information. Overall, there is evidence of a relationship between source monitoring errors and the disorganized thinking that characterizes those who have schizophrenia in that there is a strong tendency for those people with hallucinations to attribute their internally generated events (i.e.: hallucinations and delusions) to an external source (e.g., the experimenter). That is, schizophrenia is characterized by failing to encode themselves as the source of the idea, compounded by attributing these ideas/beliefs to an external source, all of which leads to those individuals with schizophrenia exhibiting behaviours typical of those with source amnesia; they misattribute the source of their knowledge, ideas, or beliefs.
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