**6. Neurological diseases**

#### **6.1 Amnesia or forgetting?**

The first point to consider is determining if exists amnesia or forgetting: It is not the same. Although in both circumstances it shows the absence of retrieval of the elements lived by the person and how they get stored in the brain, the amnesia is produced by a real element damaging the neurons of the memory circuit. There are several conditions that could be presented in different illnesses that produced amnesia [43]. The next are the most common causes to produce it (**Table 1**):

There is much information about each one of the neurologic diseases, but this is not the discussion matter of this chapter. Those have been mentioned to show the difference between amnesia and forgetfulness.

On the other hand, forgetting is the absence of reuptake of the skills or memory elements without lesion to the brain neurons, and neuronal circuitry is intact. Sometimes normal forgetting is considered like a pathological memory problem, and this is not the real image of what exactly happens. An example could be a geriatric patient with failures in memory that could be attributed to incipient dementia. The process of forgetting is explained due to perception and/or attention alteration. Indeed, the simple past of the time could produce a diminution of the capability to retain the information entered into the brain [44, 45].

Some of the concrete neurologic problems are described below (**Table 2**).

#### **6.2 Aging**

It is well known that neuroplasticity is produced during the initial stages of the human being after-birth, when the brain is immature. It is needed for establishing


**Table 1.** *Amnesia and its causes.* *Neurophysiology Involved in Neuroplasticity: Mechanisms of Forgetting DOI: http://dx.doi.org/10.5772/intechopen.105129*


**Table 2.**

*Concrete neurologic problems affecting memory.*

connections and making neural circuits that could regulate basic and important levels of diverse functions in the Central Nervous System (CNS) [46]. In this sense, the neuroplasticity of a newborn, and infant, and inclusive an adolescent is more relevant compared to the neuroplasticity of adult and geriatric subjects and patients. The person develops forgetting when the lifetime is passing through his eyes. It is the expected, so it is an important event, but not only the oldest people experiment it. As it has been stated, forgetting is necessary to leave irrelevant knowledge, learn and memorize new ones in each stage of his life [36, 47].

## **6.3 Sleep deprivation**

Patient with moderate-to-severe problems of sleep with different etiologies could present more frequent number of forgetting memories compared to normal subjects. The presence of insomnia is a determinant factor for the lack of concentration because it affects the attention and a correct state of consciousness. It is important the state of anatomical and functional integrities of the Reticular Ascendent Activating System (RAAS), which takes part in several neurotransmitters involved in the arousal-sleep cycle. In this matter, the orexin-neuron groups are involved in this regulation, according to what Chambers stated in 2017 [48]. To consolidate the knowledge, the hippocampus needs to have the presence of a neurophysiological plateau with the intervention of calcium (Ca++) to produce the hippocampal delta waves. Such manifestations demonstrate the consolidation of a set of skills. This is mediate by acetylcholine. It is possible that forgetting could use the same anatomical point, with the performance of inhibitory neurotransmitters like GABA or glycine [49].

#### **6.4 Hypermnesia**

One of the most interesting situations of medicine is the presence of photographic memory. It is rare to find people with this extraordinary capability. For the person who had this gift could be used in a social and economic success [50, 51]. The person with this "excess of memory" has an enormous advantage to learn and to extract information from their neuronal circuits. It demonstrated that it exists a hyper-connectivity and optimization of the function of neurotransmitters like noradrenaline, as described by Hurlemann [52]. Nevertheless, when a subject has this situation, it could be difficult to destroy superficial information, and every single moment could be remembered, everything from the big picture to the small details, depending on the individual's capability. This illness does not allow the use of forgetting, so in this person, this could give birth to a paradoxical and noxious psychological effect [53].

#### **6.5 Severe mental stress**

One of the most important defense mechanisms against brutal stress is the presence of forgetfulness when some life events, like rape or war survival, could have been lived. This produces a tremendous shock in subjects or in patients, opening the possibility of being diagnosed with "post-traumatic stress disorder" (PTSD). For lucky individuals who forget what happened, the brain uses these psychological mechanisms, described by psychologist and psychiatrist, to bury the unpleasant experience in the unconsciousness or to delete it completely from the memory [54]. It is certainly that powerful inhibitory system in the limbic and memory circuits that had been involved including dopamine, as reported by Sabanda in 2021 [55]. Patients with this trauma had mild to severe anxiety and depression [56]. These add a motive to avoid remembering painful events and could potentiate forgetting. Some studies with war veterans are performed with PET or functional MRI to know what happened in the brain lobes with stress.
