Neuropsychological syndromes of disorders of mnestic activity in patients with strokes in the right (subdominant) hemisphere

Selkin Mikhail Dmitrievich Assistant to of Department of the General and Clinical Psychology of the First St. Petersburg State Medical University named of the Academician I.P. Pavlov 197022, Russia, Saint Petersburg, Lva Tolstogo str., 6-8 medpsiholog@bk.ru

Introduction

It is generally believed that ischemic lesion of the dominant hemisphere is a serious disorder that greatly affects the patient's condition and worsens the prognosis for rehabilitation, work capacity and quality of life. Thus, it is known that a violation in the basin of the left carotid artery leads to a pronounced cognitive deficit in 46% of cases ^[17].

At the same time, damage to the vascular basin supplying the subdominant hemisphere causes cognitive deficits in 15% of cases ^[18] and this is regardless of the severity of the lesion, that is, patients with both transient attacks and irreversible deeply disabling vascular events are included in the statistics ^[20]. One way or another, any suffered cerebrovascular accident is a serious case affecting the further fate of the patient. All this points to the enormous medical and social significance of the problem.

To date, medical practice has presented data indicating the proven effectiveness of neuropsychological rehabilitation techniques, the most effective is a technique that works according to the mechanism of intersystem functional compensation. Such therapy is a factor in improving prognosis, regardless of the patient's age, gender, initial cognitive status and vascular history. At the same time, the maximum effectiveness of neuropsychological and neurodynamic therapy can be achieved by purposefully training the lost function, in this case, a type of mnestic disorder. Despite the fact that determining the lesion in modern medicine is not difficult due to visualization methods, there is no clear understanding of the attachment of a particular function of higher nervous activity to a specific site. Of course, Brodman fields effectively map the cortex and are of great neurological and neurosurgical importance, but at the same time they cannot be a good assistant for a psychologist and psychotherapist.

Recently, many innovative papers have been published studying the function of the medial temporal lobe. There are works indicating that damage to the temporal lobe is associated with impaired memory for new facts, faces, events, places ^{[3; 9]}. These disorders are attributed to different areas of the medial temporal lobe, but the issue has not been fully studied, due to the complexity. In practice, difficulties arise with the selection of patients with such a local lesion, it is difficult to conduct their research (usually due to the severity of the general condition), it is also difficult to conduct research on laboratory animals due to excessively difficult access and the great danger of damaging "superfluous" structures by coagulating the studied area of the brain (that is, turning off the function, which he is responsible for).

Recent studies in rats, monkeys and in the clinic have shifted from studying the medial temporal lobe to the hippocampus and parahippocampal furrows. Finally, the most complete study of the issue was presented by the authors ^[13], who noticed that verbal memory is impaired in left-sided lesions, and spatial memory is impaired in right-sided lesions. It turned out that subjects with a right-sided lesion of the temporal lobe were worse at remembering the location of objects presented to them 3 minutes ago (while the patients retained spatial memory for the first minutes). The authors concluded that the subdominant hemisphere, namely, the subdominant temporal lobe, interacts extremely actively with the hippocampus in encoding spatial memory, moreover, participates in its storage, starting from a few minutes after memorization ^{[1; 5; 9; 10]}

This theory correlates perfectly with newer studies ^[2]. Great importance is given to the right parahippocampal gyrus, as well as the right hippocampus. At the same time, another recent study forms a new paradigm: a right-sided lesion cannot completely "turn off" the function of spatial thinking. Only a large part of its limitation occurs. That is, the function of spatial memory is mainly assumed by the subdominant hemisphere. At the same time, the structures of the dominant hemisphere also play an important role. Maguire et al. It has been shown that when solving difficult spatial problems, mapping, and route planning, right-sided parahippocampal structures work cooperatively with left-sided ones.

It should be noted that visual memory, functioning through the work of the temporal lobe, plays an extremely important social role. In isolation, this lesion is extremely rare ^[4]. However, laboratory studies allow us to delve into the issue of visual memory impairment and the mechanisms of its compensation after any damage to the cortex ^{[14; 15]}.

Friendly interhemispheric interaction forms an adequate activity, which can be judged by the quality of memory. When such a synergy is violated, the unaffected area is disinhibited due to the disappearance that balances it ^{[8; 9]}.

Experiments were conducted on the separate and friendly involvement of the hemispheres in the assessment of visual information and memorization. It turned out that if visual information enters only the subdominant hemisphere (and the dominant one is in short supply, that is, visual information does not enter it from the corresponding field of vision), there is a disinhibition of the subdominant hemisphere, which leads to its overload and the appearance of more errors in recall. The situation worsens when the caused deficiency in the activity of the dominant hemisphere is supplemented by the need to carry out mathematical calculations of the number that needs to be remembered ^[11].

The above-described studies indicate that the disappearance of the functioning of a site in the subdominant hemisphere entails an asymmetric shift in activity towards the dominant hemisphere, which leads to disinhibition of functional areas and decreased productivity with additional cognitive load ^[6].

Deterioration of short-term memory is an important symptom of damage to both the dominant and subdominant hemispheres. This symptom is not specific, it has been described in several studies. The peculiarity of this symptom is reversibility.

Of course, it is rare to talk about the complete restoration of short-term memory, according to some data, even with intensive cognitive training, it is possible to achieve the initial quality of memory in 40 percent of cases.

The diagnosis of this symptom is reduced to a simple test for memorizing 10 words according to the method of A.R. Luria ^[12]. A satisfactory result is the reproduction of 7 ± 2 words, if it is not known how many points the patient scored before ONMC, if it is known how much the patient memorized before ONMC, then this figure is the minimum goal of rehabilitation.

Correction of this symptom is important for the complete rehabilitation of the patient. An extremely effective method of correction is a combination of cognitive gymnastics with physical exercises. The combination of general physical exercises adapted to the patient's condition with game exercises like "repeat after me" or "repeat the movements that I will name" ^[18] accelerates both spontaneous memory recovery by the mechanism of disinhibition and improves memory due to the formation of cross-functional communications of the central nervous system.

Assessment of the affected area and the "dropped out" mnestic function can occur during cognitive testing, as well as in the assessment of symptoms and syndromes.

It is the assessment of the symptoms and syndromes (that is, the clinic) of the lesion that makes it possible to plan further cognitive therapy. In this regard, the topic of the work is extremely relevant - a review of the described syndrome in patients with damage to the subdominant hemisphere.

The purpose of this study was to analyze the structure of clinical symptoms and features of impaired mnestic function in patients with acute cerebral catastrophe in the right (subdominant) hemisphere.

Research methods and principles

An analysis of the clinical manifestations of right-sided ONMC in patients of the neurological department with a dominant left hemisphere was carried out. A group of patients with right-sided ONMC, consisting of 36 respondents, was selected. The same number of people were in the comparison group.

The group includes patients without severe disorders of consciousness, motor skills and cognitive functions. The observation was carried out for 14 days, which corresponds to the acute period of ONMC. 3 data measurements were performed: upon admission, after 7 days and upon discharge (14± 1 day).

The compared groups were comparable in terms of sex ratio, age 46± 0.9 years, level of education, percentage of people engaged in labor activity at the time of the incident.

A set of patho- and neuropsychological methods was used to assess memory: "Wexler Memory Scale"), Indirect memorization according to A.N. Leontiev, the "Pictograms" technique, Benton's Visual retention, the "Memorizing 10 words" Technique, the "Memorizing faces" Technique, the "Memorizing shapes" Technique, the MoSS test.

Main results

The results of the MoHS test were compared on 5 ± 2 days of hospital stay (Table 1).

 Table 1. MoHS test results

The Montreal Cognitive Assessment Test is a simple screening method for assessing cognitive impairment (including memory). In the conducted study, the vast majority of patients had cognitive impairments, and their severity varied. The analysis showed significant differences between the two groups of subjects in terms of cognitive functions. Statistical analysis revealed that the confidence level (p<0.05) indicates statistically significant differences in the form of more pronounced cognitive impairment in patients of group 1 (with focal lesion in the dominant hemisphere). At the same time, patients of the 2nd group (with lesions in the subdominant hemisphere) showed less pronounced cognitive impairment according to the results of the same technique.

Further, more detailed testing was carried out using techniques for different types of memory. The results of testing patients in the acute period of ONMC are presented below (Table 2).

Table 2

Comparative analysis of mental activity in patients with lesions of the dominant and subdominant hemispheres at the time of admission to the hospital

The indicators of verbal-logical, operative, associative memory and indirect memorization significantly worsened in patients in both groups, however, patients with right-sided showed the best result, that is, ONMC did not have such a strong effect on memory deficit.

The analysis of the ONMC clinic in the right (subdominant) hemisphere, depending on the site of the lesion, was carried out (Table 3).

Table 3

Descriptive characteristics of mnestic activity in patients with subdominant (right) hemisphere lesion depending on the affected area

In a group of 10 patients with lesions in the occipital lobe of the right hemisphere, a reduced ability to form semantic connections was revealed. According to the method of "Story Reproduction", the average value was 6.5 ± 0.9 points out of a maximum of 23, which corresponds to 30% of the norm (80-100%). Such a low indicator indicates significant difficulties in perceiving and understanding a coherent text.

Along with this, this study notes the possible involvement of the temporal lobe of the right hemisphere in the pathological process. The difference in indicators between the occipital and temporal lobes is insignificant: in the study of visual-verbal memory using the "Paired Associations" method, the average value was 10.1 ± 0.8 points out of 21, which corresponds to 52% of the norm (80-100%). This result indicates difficulties in establishing associative links between visual and verbal stimuli.

Damage to the occipital lobe of the right hemisphere is also accompanied by a decrease in visual memory. The "Visual retention" technique revealed an average value of 2.6 ± 1.3 points out of 10, which is lower than the standard indicators (7-10 points). This disorder manifests itself in difficulties in memorizing and reproducing visual images.

The study by E.D. Chomskaya showed that damage to the left hemisphere in the occipital lobe also leads to visual memory disorders, especially in relation to visual stimuli. At the same time, the volume of visual-speech memory narrows, which makes it difficult to memorize and reproduce coherent visual-verbal material.

The combined lesion of the parietal and occipital lobes of the right hemisphere causes pronounced disorders of indirect memorization, memory for faces and geometric shapes. Patients have difficulty using auxiliary tools (for example, prepared maps) to improve the efficiency of memorization. The technique of "Indirect memorization according to A.N. Leontiev" showed average values of 63.4 ± 19.3 and 67.7 ± 26.2 points out of 90-100.

When the parietal lobe of the left hemisphere is affected with the involvement of the occipital regions, memory disorders for visual images are noted. The technique of "Memorizing shapes" revealed average values of 2.1 ± 0.6 and 3.1 ± 1.3 points out of 7-10, which indicates difficulties in memorizing and reproducing geometric shapes.

In general, damage to the occipital-temporal-parietal parts of the brain has a complex effect on various aspects of memory. Violations of visual, associative and episodic memory lead to a decrease in the ability to perceive, understand and remember information, which significantly complicates the adaptation of patients to the environment and daily activities.

With insufficient functioning of the temporal lobe of the right hemisphere (PV), violations of operational (fixation) memory are observed, which manifests itself in low indicators in the test "Memorizing 10 words" at the first presentation: 3.9 ± 1.6 (with a norm of 7 ± 2 words). This may be caused by the spontaneity of cognitive activity, general asthenization and an insufficient level of spontaneous initiation of activity. Similar disorders can be observed when the same area is affected in the left hemisphere. However, the process of further memorization of information indicates the involvement of the parietal and occipital lobes in it, which contributes to the effective retention of information.

The temporal lobe plays an important role in long-term memory and recall of auditory-speech information. A low level of logical memorization by visual reinforcement using drawings using the "Pictogram" technique is associated with insufficient functioning of the temporal and occipital lobes of the right hemisphere (53.4±23.4 and 55.2±6.7, with a norm of 75%).

At the same time, the left temporal lobe plays an important role in auditory-speech memory and information storage, since speech zones are located in this area. At the same time, verbal semantic memory is more associated with the left (dominant) half of the brain, while the right temporal lobe is responsible for episodic memory.

Conclusion

In patients with cerebral infarction in the left and right hemispheres, there are differences in the specifics of disorders of mental activity. When the right hemisphere is affected, the main disorders are inertia of memorization and difficulties in remembering faces and figures. When the left hemisphere is affected, the most pronounced violations are noted in verbal-logical, operative and associative memory.

The analysis of the characteristics of the course of mnestic activity makes it possible to identify syndromic violations of its individual functions. Thus, when the right temporal lobe of the brain is affected, there is a decrease in operational (fixation) memory. The lesion of the right occipital lobe (subdominant) leads to visual memory disorders (memory for faces and geometric shapes). Damage to the occipital and temporal lobes mainly leads to a violation of associative memory. The lesion of the parietal-occipital lobe corresponds to a violation of logical memory. The lesion of the temporal-parietal-occipital lobes of the right hemisphere is characterized by a violation of direct (mechanical memorization) and semantic memory.

Along with the impaired functions, it is important to note the preserved memory components. When the temporal lobe of the right hemisphere is affected, visual and logical memory remain the most functional. In case of damage to the parietal and occipital lobes, the operative (fixation) remains more intact. At the same time, visual and associative memory show high performance in case of parietal lobe deficiency.