anosognosia Flashcards
define anosognosia
Anosognosia refers to a state in which patients deny their deficits following brain injury. Anosognosia for hemiplegia is the most extensively studied. This is when the patient denies paralysis of a limb. AHP is more common after right brain damage than left, indicating that the right hemisphere is important for awareness of disability. Case studies have shown that there are implicit and explicit forms.
Describe motivational theory (Weinstein 1991)
which uses a psychodynamic approach, anosognosia is an adaptive response to avoid distress or catastrophic reaction to the recognition of disability. It is thus a form of psychological defence where the patient denies too painful a situation in order to maintain intact psychological balance. This theory further suggests that a certain personality type mediates the development of denial. In their study, they compared premorbid personality traits between two groups of patients who differed in terms of whether or not they explicitly denied deficits. Their results indicated that patients who develop anosognosia are those who tended to consider illness a weakness or sign of failure and were strongly concerned about the opinion of others. The motivational theory has been criticized for a number of reasons and various inconsistencies have been shown regarding psychologically motivated denial as an explanation for AHP.
Evidence against motivational theory
Levine et al (1991) and Small & Ellis (1996), which used personality inventories, fail to uncover the personality temperaments associated with AHP.
McGlynn & Schachter, 1989 note that motivation theories do not consider the specificity of anosognosia. For example, if AHP is a denial mechanism, this implies that at some point, the patient must have processed to some extent that they had a deficit and therefore, they should on some level have knowledge of the deficit in order to trigger anosognosia (Coccchini et al., 2009). Based on this, it would be expected that anosognosics would have some implicit awareness of their disorder, but research has demonstrated to the contrary.
Doesn’t consider anatomical basis- it follows brain damage. If it was a defense meachanism we would expect to see it following brain damage in general.
Study against motivational theory
One method often used to asses implicit awareness of hemiplegia is to ask the anosogosic patient to carry out a task which could be done more easily using both hands (bimanually) or could also completed with slightly more difficulty using one hand, for example lifting a tray. It is expected that if a patient is implicitly aware of their hemiplegia, they will attempt the uni-manual task as they know implicitly that they will not be able to perform it bimanually. Cocchini et al (2010) asked eight anosognosic patients to complete such tasks. Whilst it was found that the majority of the patients did demonstrate implicit awareness, there were still one quarter of patients who demonstrated no implicit knowledge of their disorder and continued to attempt the impossible bimanual task. Therefore, in opposition to the motivational theory of anosognosia, information about disability has not necessarily been processed or recognised on even an implicit level
Feed Forward Theory (Gold et al 1991)
AHP is the result of a deficit of the intentional system in formulating expectations of movement. Heilman suggests that in a normal functioning individual, our intentional system is activated simultaneously with our motor system to perform a movement. A body representation about the specific movement is continuously compared with afferent information. If the comparator system and body representation identify a mismatch between expectations of movement and the actual failed performance of movement, the patient is aware of their deficit. If however there is damage to the intentional-preparatory system, this leads to an absence of their expectations to move their paretic limb, i.e. anosognosic patients do not have preparatory intentions to move. Hence the comparator system fails to recognize any mismatch, resulting in the unawareness to detect motor or movement failure.
Evidence for feed forward theory
Gold et al (1994) provided evidence for this by testing motor intention and measuring the activation of proximal muscles in participants whilst they squeezed a dynamometer with each hand. Participants included a group of normal controls, brain damaged controls and one patient with persistent AHP. The AHP patient did not contract either of his pectoralis muscles when asked to squeeze with his contralesional, paretic hand, yet he contracted both of them when squeezing the dynamometer with his ipsilesional hand. Controls contracted both pectorales when asked to squeeze with each hand. This demonstrates a loss of motor intention and lends support to the feed-forward hypothesis of AHP
Gondola et al (2014)
conducted a study in which a patient known as GC with anosognosia for hemiplegia (AHP) was required to attempt to produce hand movements (touching each of his fingers to his thumb). There were three conditions regarding carrying out the hand movements. In one condition, GC was asked if he thought he would be able to produce the hand movement, in a second condition GC was asked to attempt the movements with his eyes open and in the final condition GC was asked to attempt the movement with his eyes closed. Transcranial direct current stimulation was applied to the premotor cortex to disrupt activity there. The three movement conditions were carried out under sham TDCs, actual TDCs and post TDCs. Results showed that GC has reduced anosognosic syptoms (i.e. was more able to realise that he was unable to perform the hand movements) under the condition where his eyes were open after activity in the premotor cortex had been inhibited using the TDCs. These results suggest that usual activity in the premotor cortex i.e. the intention to move, usually overrides the visual feedback of the non-moving hand. Thus when the motor intention are disrupted and the visual feedback of the non-moving hand was not overridden, GC’s anosognosic symptoms reduced.
Discovery theory (Levine, 1990)
According to this theory, a loss of function does not produce any immediate experience of loss but must be “discovered” via a process of self-observation and inference. Inadequacies in observations/own inference means that an impaired bodily sensation, coupled with any other additional cognitive deficits eventually leads to persistent unawareness and denial of impairment, indicating that sensory feedback is of particular importance (Heilman, 2014). In other words, recognition of AHP requires self-observation and personal recognition of the failure to perform tasks involving movement of the paretic limb. The lack of proprioceptive information in addition to other cognitive deficits that co-occurring, do not enable the patient to make the discovery of illness/paralysis.
Levine et al 1991
Evidence supporting this theory was shown by Levine et al. (1991) who compared six patients with right hemisphere stroke AHP lasting 1 month or more with seven right hemisphere stroke patients whose AHP had lasted only a few days. All patients with persistent AHP had severe sensory loss to the left side of the body and had more severe left hemispatial neglect. These patients showed impairments in tests of memory and intellect, and had impaired mental organization, reduced mental flexibility, and poor mental control
Further limitations of discovery theory
. However, this can also be viewed as a limitation to theory, as it has been well established by double dissociations that anosognosia does not appear to be due to global cognitive deficit, but rather a complex combination of very specific modular deficits. For example, Berti et al (1996) described a patient who had anosognosia for the hemiplegia of her upper limb, but was aware of the hemiplegia for her lower limb. Von Hagen and Ives (1937) describe the opposite in a patient who had anosognosia for hemiplegia of the lower limb but acknowledged hemiplegia of the upper limb.
