As a first step towards clarifying the range of defects to which collective memory may be vulnerable, it is appropriate to consider those of individual memory (81). In each case below these are described in such a way as to point to the nature of the possible equivalent in the case of collective memory. The order is not significant.

(a) Transient global amnesia

This consists of an abrupt loss of memory, lasting from a few seconds to several hours, without any loss of consciousness. No information is stored for that period and thus there is complete loss of memory. Such attacks may be recurrent and are thought to result from temporary reductions in blood supply to specific areas of the brain (possibly presaging a stroke). Actions may continue to be performed automatically during the attack (traumatic automatism).

Analogous phenomena may occur in the case of collective memory

(b) Traumatic amnesia

Following recovery of consciousness after cerebral trauma caused by a head injury a person is typically dazed, confused, and imperfectly aware of his whereabouts and circumstances. During this state it is not possible to store new memories. On recovery the person may be unable to recall this period (post-traumatic amnesia) and may exhibit memory failure concerning brief or long periods into the past (retrograde amnesia). Subsequently memories may gradually return and be interrelated in an appropriate time sequence.

Analogous phenomena may occur in the case of collective memory as a result of natural disaster or major social upheaval (war, revolution, eta), or as a result of damage to some particular repository of collective memory.

(c) Retrograde amnesia

This consists of loss of memory for events that occurred at a time when brain function was unimpaired. It is therefore generally due to failure of retrieval although this is usually very selective - "islands" of memory in a "sea" of amnesia often emerge.

An analogous phenomenon may be encountered in collective memory. For example, particular incidents may be recalled, and reflected in various repositories, although there is loss of memory concerning the processes which connected them together and with the present.

(d) Hysterical amnesia

One form of this involves failure to recall particular past events, possibly in a particular period. In another form there is failure to register current events and subsequently to recollect them. In both cases the memories may influence behaviour although thy resist efforts at recollection, Such memories are usually painful and are repressed as a psychological defence. (It is characteristic that they may be recovered under hypnosis).

Analogous phenomena may occur in the case of collective memory. In bureaucratic environments they are associated with the process of "burying" some unpleasant file of information if only by severely restricting its distribution. Or alternatively it will be carefully arranged that no file is created in the first place. The media and politicians often act on the assumption that the public will "forget" some unpleasant item of information.

(e) Alternating amnesia

In this condition two separate states of consciousness alternate with one another, during each of which there is no memory for events that occurred during the other. Each state is a complex set of memories, attitudes and behaviours with distinctive characteristics, and is sequentially and disjointedly manifested. (This is a form of hysterical amnesia).

Analogous phenomena may occur with collective memory, segments of which may be activated and expressed sequentially but without reference to each other. One possible indication of this is when a body of individuals convene in one mode and subsequently reconvene in another mode ("wearing different hats") in which it is "inappropriate" to make any reference to the previous occasion.

(f) Hypnotic amnesia

Amnesia may be induced by the use of suggestion usually under hypnosis (in a trance state). Memory of the trance state is vague and fragmentary, especially if the suggestion is that it should be forgotten.

Analogous phenomena may be found with collective memory. Public opinion may be "hypnotised" by suitable processes (perhaps fascist propaganda is an extreme example) and these may well cause awareness of the "hypnotised state" to be collectively repressed.

(g) Aphasias

These impairments of the formal language code in verbal communication are due to circumscribed cerebral 1esions.They may be grouped as follows:

• Disorders of spoken language:
• Expressive aphasia such as phonemic aphasia, disorder of syntactic production (agrammatism), and disturbances of repetition
• Amnesic aphasia, namely disturbances in word recall and inability to name
• Sensory aphasia, namely incapacity to interpret verbal auditory stimuli (despite normal hearing), disorders of understanding (affecting implementation of instructions), and disorganisation of attention (distractibility, or entrapment in a repetitive speech pattern).
• Disorders of written language, including the reproduction of graphemes.
• Disorders of reading include general disintegration of the sense of word structure and phonic graphic correspondence affecting copying and spelling (alexia-graphia) but may be limited to reading (alexia) with erroneous efforts at compensation.

In the case of collective memory, there may be analogous disturbances in decoding and encoding between the various modes. In the operations of the international community there are many instances of systematic weaknesses in spoken communication, and inability to "read" available texts with any efficacy. There is often a hiatus between the two modes.

(h) Paramnesia and confabulation

These are errors and illusions in memory and their reproduction. They may consist of: treatment of fantasies as genuine events, belief that events similar to a unique event have previously occurred (reduplication of memory), or belief that an event identical to a previous event has previously occurred (déja vu). Whilst all remembering depends heavily on reconstruction rather than on mere reproduction alone, confabulation is a highly error prone form of production of spurious memories and fabrications.

Analogous phenomena may be found with collective memory particular in some of the abuses of speech-makers and the media whereby facts are "invented" which appear to fit the context of a presentation. These processes may also be associated with the important phenomena of rumour in establishing public opinion.

(i) Korsakoff's syndrome

This is a complex syndrome defined by four possible conditions:

• gross defect in recent memory (associated with retrograde amnesia) although memory for remote events and didactically learned facts remains intact
• a spatial or temporal disorientation
• some degree of confabulation
• false recognition

It occurs in a wide variety of toxic and infectious brain illnesses as well as in association with some nutritional disorders. The syndrome may be so severe as to produce "moment-to-moment" consciousness, with information only being retained for a few seconds and providing no continuity between one experience and the next. Learning may thus be severely limited or impossible. The condition can be transitory or chronic.

Analogous phenomena may occur in the case of collective memory in social conditions of extreme deprivation or disorganisation.

(j) Memory defects of special origin

Memory disorders usually result following brain surgery, encephalitis (brain inflammation) or electro-convulsive therapy. Those of the first case may well resemble those of the second which themselves resemble those of Korsakoff's syndrome. However the individual in both cases recognises the memory difficulty. Frequent electro-convulsion sometime leads to exaggerated forgetfulness for day-to-day events.

Analogous phenomena may occur in the case of collective memory as a result of physical destruction of portions of an information system, uncontrolled hyper-development of such a system, or the subjection of such a system to frequent overload beyond the breakdown threshold.