Patients with frontal lobe damage do not show the obvious deficits of the temporal lobe patients. However it is recently discovered that frontal lobe lesions cause subtle memory impairments. The first study showing an impairment was done by Prisko in 1963. The task was to tell whether two successively presented stimuli were the same. Different modalities were tried for the stimuli, clicks, lights, tones, colors, nonsense patterns, etc. The difficulty of the task comes from the requirement to suppress the stimuli from previous trials and concentrate on the last sample. The frontal lobe patients were found impaired in this task.
Corsi later discovered that these patients were impaired in their memory for the ordering of the events. The task Corsi used was to present the subjects with cards that had pairs of pictures or words on them. Occasionally a card was presented with a question mark between the pair. At that point the subject had to tell which of the pictures he had seen more recently. If one of the stimuli is one that has never been seen, then this is a simple recognition task. If both are seen before, then this task requires a comparison of recency. Patients with left temporal lesions are impaired in recognition. The frontal lobe patients intact in recognition but impaired in the recency task.
Moskovitch and Milner tested the frontal lobe patients for release from proactive interference. The task was recall of word lists. Four sets of 12 words of the same category followed by a set of 12 words from a different category are presented. Normal subjects decrease their performance from set 1 to set 4 due to interference. Typically they do as good as the first set in their fifth set. Frontal lobe patients did not get much better in their fifth set. Similar results were observed in Korsakoff's patients but not in temporal lobe patients.
Kolb and Milner discovered deficits in movement copying. An example task was to copy a series of three discrete facial expressions. The frontal lobe patients were observed to make intrusion and omission errors. Part of this impairment might be due to short term memory deficits.
Cortical injuries in the other parts of the brain occasionally cause specific long-term memory difficulties. These deficits are typically very selective and limited to a particular domain. Examples include color amnesia, prosopagnosia (face amnesia), object anomia (inability to remember names of objects), topographical amnesia (inability to remember locations of objects).
Other cortical lesions may also cause short term memory deficits. Warrington and Weiskrantz studied several cases of short term memory deficit. Most likely areas to cause short term memory disorders are the polymodal sensory areas of the posterior parietal cortex, posterior temporal cortex, and the frontal lobes. Short term memory deficits specific to verbal or visual stimuli have been observed. These results imply that STM and LTM are parallel processes and material is processed separately by both.
Korsakoff's disease is another source of severe amnesia. It is seen in chronic alcoholics and thought to be due to lack of vitamin B1. The disease results in degeneration of medial thalamus, mamillary bodies and generalized cerebral atrophy. Symptoms appear within a few days. Sanders and Warrington describe six major symptoms in their seminal paper on Korsakoff [Sanders and Warrington, 1971]. Anterograde amnesia, general retrograde amnesia (unlike temporal lobe patients), confabulation (making up plausible stories for past events), lack of insight (they are typically unaware of their defect), and apathy. Most of these symptoms are clearly in contrast with temporal lobe patients like H. M. Temporal lobe patients show normal release from interference, frontal lobe patients and Korsakoff patients do not. Korsakoff's patients have extensive loss of past memories before the damage, temporal lobe patients do not. Moskovitch suggests that Korsakoff's syndrome is accompanied by frontal lobe deterioration. Korsakoff's patients have normal IQs and other cognitive capabilities are intact in general.