**3. Autobiographical memory**

#### **3.1. Autobiographical memory: what it is and its main characteristics**

Autobiographical memory (AM) is part of the episodic memory, as it deals with specific memories accompanied by a temporal and spatial context. However, the main characteristic that defines autobiographical knowledge and makes it distinctive is that the memories form part of a personal context because they are experiences the person had throughout the life cycle [24]. Generally, autobiographical memory consists of information about places, actions, people, objects, thoughts, and emotions. Some authors define it as the memory of our *self* (of our identity) in relation to the world and other people [22–25]. Thus, autobiographical memories, in addition to being situated in a specific time and place like any other memory, are also related to the individual; that is, the person experienced the past event to be remembered first-hand, and he/she is not only aware of the objective event, but also his or her own feelings, perceptions, and interpretations.

Although it is true that AM is based on episodic memory, there is also another much more generic and abstract type of autobiographical memory. AM involves two types of knowledge about oneself: episodic and semantic [26]. The episodic component consists of personal and specific events located in a specific place and time, and the semantic component stores general knowledge from the past, such as names, addresses, or general events [27–30].

These two components are associated with a different state of consciousness [31]: on the one hand, autonoetic consciousness, associated with the episodic component and, on the other, noetic consciousness, associated with the semantic component [32, 33]. Autonoetic conscious‐ ness is defined as the feeling of re-experiencing or reliving a past event, in other words, subjectively traveling in time to our past. Not only is the event itself recalled, but sensoryperceptual details derived from the event are also recovered, that is, experiences that contain perceptual, affective, and temporal-spatial details. They give the memory a personal meaning that makes it form part of our identity and goes beyond mere knowledge. By contrast, noetic consciousness is the capacity to know or have certain information about the world or about our lives, without any contextual details.

Some studies [34–36] show the dissociation between aspects of the two types of consciousness in aging. As we age, we go from an autonoetic consciousness to a noetic consciousness. Therefore, with age, the semantic component of autobiographical memory increases, whereas the episodic component decreases.

Along the same lines, the AM forms part of the remote memory and, therefore, that its initial nature is episodic [37]. However, they propose that this information can gradually lose its contextual association and the details about a specific place and time, gradually acquiring semantic characteristics, with a generic and decontextualized organization like other semantic knowledge.

#### **3.2. Localization of autobiographical memories**

therefore, can be worked with as a way to improve the emotional well-being of patients with

One of the aspects most linked to emotional well-being is the feeling of identity. People who have AD have limited access to the autobiographical memories related to identity mainte‐

Along these lines, the autobiographical memory (AM) plays a fundamental role in the construction and conservation of personal identity [20]. It is indispensable for maintaining a sense of continuity and understanding the self throughout the life cycle. In addition, it contributes to the development of daily activities such as social relationships, decision making,

Memories related to personal events from the past are much more complex and emotional than nonautobiographical memories, and they also contain more intimate information related to the self [22, 23]. Thus, they are more likely to be kept in the memory than nonautobiographical

Therefore, autobiographical memories are an essential aspect in the progression of AD because they allow the preservation of the identity, which will contribute to the development of positive

Autobiographical memory (AM) is part of the episodic memory, as it deals with specific memories accompanied by a temporal and spatial context. However, the main characteristic that defines autobiographical knowledge and makes it distinctive is that the memories form part of a personal context because they are experiences the person had throughout the life cycle [24]. Generally, autobiographical memory consists of information about places, actions, people, objects, thoughts, and emotions. Some authors define it as the memory of our *self* (of our identity) in relation to the world and other people [22–25]. Thus, autobiographical memories, in addition to being situated in a specific time and place like any other memory, are also related to the individual; that is, the person experienced the past event to be remembered first-hand, and he/she is not only aware of the objective event, but also his or her

Although it is true that AM is based on episodic memory, there is also another much more generic and abstract type of autobiographical memory. AM involves two types of knowledge about oneself: episodic and semantic [26]. The episodic component consists of personal and specific events located in a specific place and time, and the semantic component stores general

These two components are associated with a different state of consciousness [31]: on the one hand, autonoetic consciousness, associated with the episodic component and, on the other,

knowledge from the past, such as names, addresses, or general events [27–30].

**3.1. Autobiographical memory: what it is and its main characteristics**

AD.

452 Update on Dementia

nance, self-knowledge, and self-image.

memories, even in pathological aging.

emotions or emotional well-being.

**3. Autobiographical memory**

own feelings, perceptions, and interpretations.

or problem solving [21].

Regarding the temporal distribution of autobiographical memories throughout the life cycle, have been revealed a similar pattern of memory localization in older people [38, 39]. This irregular pattern is characterized by three key memory points: childhood amnesia, the reminiscence peak or *bump*, and the recency effect (see **Figure 1**).

**Figure 1.** Localization of autobiographical memories.

#### *3.2.1. Childhood amnesia*

Memories from the first years of life are practically nonexistent, a phenomenon known as childhood amnesia. This absence of memories occurs because up to the age of 5, the brain structures that make it possible to codify and store memories are not fully developed. Everyone presents an almost complete absence of memories coming from the first years of life [40].

#### *3.2.2. The reminiscence bump*

From 10 to 30 years old, we have a large number of memories; in fact, it is the period in life that is remembered the most. Research shows that the memories most evoked by older people are those that took place during adolescence and early adulthood [41], which makes sense given that the majority of a person's relevant life events take place in this phase, such as the first love, first job, wedding, or in many cases, emigration to other places.

#### *3.2.3. Recency effect*

The last phenomenon presented on the autobiographical memory curve is the "recency effect". This effect involves events that took place in recent years, that is, a person's most recent memories. As time passes, the "recent" memories become "remote" and lose quality [42]. This fact can be observed in the figure, where, from the point of recency backward, the number of memories is lower as one tries to remember times further in the past.

#### **3.3. Autobiographical memory during aging**

Scientific research has pointed out that, as the years go by, the aging process affects memory in general. With regard to autobiographical memory, research reveals that there is deteriora‐ tion in the episodic part of autobiographical memory in standard aging. Most studies have compared young subjects (about 35 years old) to older subjects [34, 43–47], but other studies have reported a progressive decline in episodic autobiographical memory, comparing healthy subjects aged 50–100 [35, 36, 45, 48, 49]. However, the fact that the loss of episodic details leads to a greater production of semantic memories can be interpreted as a process of **"semantiza‐ tion**" of autobiographical memory. In other words, the episodic memory is not lost, but instead it becomes semanticized [34, 35].

Nevertheless, even though AM decreases with age, there are memories that revive affective and perceptual details, present spontaneity, and mix the perspectives of field and observer [36]. This may be due to the fact that certain autobiographical memories are characterized by defining our identity, as they contain affective and visual imaginary aspects with a high level of practice (due to being narrated many times). They also have a high level of personal relevance and are linked to similar memories that share the same topic and accessibility [50].

#### **3.4. Autobiographical memory decline in the course of Alzheimer-type dementia**

Numerous studies have investigated the AM losses experienced by subjects with AD. Most studies agree that there is a deficit in this type of memory [37, 51–58], but there is disagreement about the pattern of the deficit: which component is more deteriorated, the episodic or the semantic? Which memories show a greater degree of decline, the recent ones or the remote ones?

All the studies agree that in AD, the episodic component of AM is deteriorated [37, 48, 54, 55, 57, 59–61]. In other words, there are great difficulties in mentally reviving past events and phenomenological aspects such as visual images [48]. In this direction, it has been shown that patients with AD presented a worse capacity to recover specific autobiographical events [62], a deficit related to the lack of ability to mentally recover these events. This loss leads to the decontextualization or semantization of autobiographical memories, and a change in the ability to mentally recover events from the past. Thus, AD patients have a more general feeling of familiarity, expressed as the feeling of "having experienced this before".

In the case of semantic autobiographical knowledge, the conclusions do not coincide. On the one hand, some studies observe impairment in this type of autobiographical knowledge from the first stages of the disease [54, 57], while others point out that it is preserved until moderate phases of the disease [48, 63, 64].

#### **3.5. Loss of identity**

*3.2.1. Childhood amnesia*

454 Update on Dementia

*3.2.2. The reminiscence bump*

*3.2.3. Recency effect*

Memories from the first years of life are practically nonexistent, a phenomenon known as childhood amnesia. This absence of memories occurs because up to the age of 5, the brain structures that make it possible to codify and store memories are not fully developed. Everyone presents an almost complete absence of memories coming from the first years of life [40].

From 10 to 30 years old, we have a large number of memories; in fact, it is the period in life that is remembered the most. Research shows that the memories most evoked by older people are those that took place during adolescence and early adulthood [41], which makes sense given that the majority of a person's relevant life events take place in this phase, such as the

The last phenomenon presented on the autobiographical memory curve is the "recency effect". This effect involves events that took place in recent years, that is, a person's most recent memories. As time passes, the "recent" memories become "remote" and lose quality [42]. This fact can be observed in the figure, where, from the point of recency backward, the number of

Scientific research has pointed out that, as the years go by, the aging process affects memory in general. With regard to autobiographical memory, research reveals that there is deteriora‐ tion in the episodic part of autobiographical memory in standard aging. Most studies have compared young subjects (about 35 years old) to older subjects [34, 43–47], but other studies have reported a progressive decline in episodic autobiographical memory, comparing healthy subjects aged 50–100 [35, 36, 45, 48, 49]. However, the fact that the loss of episodic details leads to a greater production of semantic memories can be interpreted as a process of **"semantiza‐ tion**" of autobiographical memory. In other words, the episodic memory is not lost, but instead

Nevertheless, even though AM decreases with age, there are memories that revive affective and perceptual details, present spontaneity, and mix the perspectives of field and observer [36]. This may be due to the fact that certain autobiographical memories are characterized by defining our identity, as they contain affective and visual imaginary aspects with a high level of practice (due to being narrated many times). They also have a high level of personal relevance and are linked to similar memories that share the same topic and accessibility [50].

Numerous studies have investigated the AM losses experienced by subjects with AD. Most studies agree that there is a deficit in this type of memory [37, 51–58], but there is disagreement

**3.4. Autobiographical memory decline in the course of Alzheimer-type dementia**

first love, first job, wedding, or in many cases, emigration to other places.

memories is lower as one tries to remember times further in the past.

**3.3. Autobiographical memory during aging**

it becomes semanticized [34, 35].

As mentioned above, AM is necessary for the development and maintenance of personal identity. Autobiographical memories contribute to the development of social relationships, decision making, or problem solving [21].

Patients with AD have limited access to memories that make up their self-awareness, selfknowledge, and self-image, leading to a compromised sense of identity. This problem has been evaluated in various studies, observing that poor autobiographical knowledge was signifi‐ cantly correlated with a weak sense of identity [54].

However, based on the fact that remote memories are better recalled than recent ones, at least until moderate phases of AD, certain personal memories would be expected to be relatively preserved in the memory. These memories probably come from the reminiscence bump stage, which includes the most important events that have defined their life stories. This stage is the one most studied in the literature, as it is the memory component most related to identity and, therefore, contains more self-defining memories and events with a high emotional charge and a strong impact on the sense of identity [22].

Along the same lines, many studies have investigated the effect of AD on self-defining memories. One of these studies pointed out that most of the autobiographical memories of participants with AD also came from their reminiscence bump. However, it has also been shown that the subjects with AD contribute fewer specific self-defining memories, compared to control subjects [45]. Therefore, self-defining memories, or memories that are highly relevant to one's self-image, seem to decline from moderate stages of AD, which can explain the reduced sense of identity that occurs in this disease. Even so, it should be mentioned that in AD the semantic component of autobiographical memory is maintained until moderate phases of the disease. Different studies have shown that the personal semantic memory contributes to numerous cognitive processes related to self-referential thinking, as a reflection of the self in the past, imagining the personal future, and maintaining one's self-identity [65]. In fact, the semantic AM supports the knowledge about personal traits, roles, thoughts, and beliefs, aspects related to self-referential thinking, which is highly conceptual and independent from the medial temporal lobe [65]. Therefore, semantic AM, which is relatively preserved in the initial and moderate stages of AD, can be used as an aid to improve self-identity and selfcontinuity, and to develop the self-referential cognition strategy.

#### **3.6. Clinical rehabilitation of the autobiographical memory in AD**

The objective of the clinical rehabilitation of the AM in AD is to recover, as much as possible, the inaccessible memories, or at least maintain the "pool" of autobiographical memories that are still available. There are different therapeutic strategies, one of which is reminiscence therapy.

This therapy focuses on the conscious recall of personal memories from one's life in order to report, think about, tell, or show something about our experiences from the past. Reminiscence was originally proposed by Butler [66], who has promoted it as a tool to improve well-being and reduce depressive symptoms in older adults. Since then, reminiscence has been widely applied in cognitive rehabilitation in aging, including in pathologies like AD.
