Aphasia is an extreme form of cognitive impairment. A problem or injury to the dominant cortex causes a dysfunction in speech and writing.
Injury affecting the Broca’s area or Wernicke’s area or both cause aphasia. These areas are located in the left hemisphere of the brain in 80% of people. Broca’s area is situated below the motor cortex representing the face. It specialises in the expression of speech. A lesion here allows the patient to understand language and conversation but he cannot speak coherently. He can also pronounce well but there is no flow in the language.
The words come out abruptly at intervals. If Wernicke’s is the area affected, the patient does not comprehend correctly what is being said to him. He can understand simple instructions and respond when called by name. However he cannot understand a conversation. Talk is incongruent and coherent but is spoken at odd instances. He speaks a few words which are not connected to the occasion.
When asked a question, he responds with another phrase as answer very much out of context. Wernicke’s area is situated above the left temporal auditory cortex.Amnesia Memory loss, a feature of cognitive impairment, is the delay or failure to recall recent or distant events. Amnesia is an extreme form of memory loss when caused by a more severe injury to the brain, probably in a road accident, bomb explosion or shooting incident. Involvement due to injury or aging can produce loss of memory of varying levels. Loss can be a mild dysfunction (MCI) or severe and named as dementia.
Old people of 55-80 years of age could have cognitive impairment without having any illness.Memory loss is seen in degenerative disorders or dementias like Alzheimer’s, traumatic brain injuries, following ECT or in Korsakoff’s psychosis. Various studies have been conducted to delve into the mysteries of the aphasias and amnesias. Relearning capacities by patients who have recovered from the injuries or lesions which resulted in the impairment have also been studied.
Other studies have been done to study the relationship of cognitive impairment to the part of the brain which subserves the function. I have selected two studies which are on the aphasias and one on amnesia. First studyThe study by Staczcak (Stanczak et al,2006) was on two patients with different kinds of aphasias. The aim was to investigate how each would fare with the training techniques for rehabilitation following on their partial recovery from their Cerebrovascular accidents. Both patients were right handed, monolingual English speaking participants from Boston.
The patient SA had a CVA involving the temporal-parietal lobe. She had conduction aphasia i. e. mainly phonological defects while the other patient RB had a CVA involving the temporal/parietal lobe extending to the frontal lobe.
So he had semantic deficits too.Application of Plaut’s model and the Complexity account of Treatment Efficacy were investigated in typicality based learning and generalisation. Both were severely anomic and had same-category aphasias and Aphasia Quotient determined by the Western Aphasia Battery. Both had weekly treatment of 2 hours. SA was trained on 8 atypical vegetables and 8 typical birds.
RB was trained with 8 typical vegetables and 8 atypical birds. Differences of typicality based learning and generalisation could be assessed within and across participants. Repeatedly naming articles was the procedure adopted for training.At the final attempt the patient should be naming correctly. If not the training is repeated. SA named more birds than vegetables and more atypical items than typical.
Semantic scores were high. Post treatment scores in phonology improved but repetition score decreased. After treatment, RB showed good response for naming equal numbers of vegetables and birds and typicality was same. However maintenance of performance was poor. Both SA and RB learned typical items more quickly.
Her inability to learn atypical items was due to her mild semantic deficits. RB’s performance on atypical items improved.So persons whose injury involved the pre-frontal cortex performed better in the face of competition. SA showed no generalisation by learning while RB showed significant generalisation. Later it was found on follow-up that SA did not improve while RB improved a great deal. This study concluded saying that long term training could bring about good effects in cognitive disorders but other factors affect learning and generalisation.
Second Study ( McClelland et al) The second study by McClelland et al relates to the role of the hippocampus, the region of the brain which subserves recent memory.The study suggests that memories are first stored in the injured hippocampus via synaptic changes. These changes support the reinstatement of recent memories in the neocortex. The hippocampus allows rapid learning of new materials without influencing the neocortex. Reinstatement of new memories is possible into the structured neocortical memory systems. Bilateral lesions to the hippocampus and related structures produce a sudden onset of temporally graded retrograde amnesia.
If the hippocampus is left intact and alone, it is seen that there is gradual recovery over time, maybe 15 years, and called consolidation.When large portions of hippocampus are removed the person loses his ability to learn new things. He retains the memory of things he learned before having the injury. This is anterograde amnesia. The patient has very little memory of events and experiences before this removal. He may have a little memory of recent events and training, other intellectual functions and information processing skills.
He is amenable to selective types of learning. The hippocampus is essential for the retrieval of events and experiences in one’s life. Declarative memory and episodic memory are mediated at the hippocampus.Learning arbitrary paired associates needs a complete hippocampus. It also permits the making of appropriate responses through specific combinations of cues as evident from animal literature. Memories of places and locations are mediated through the hippocampus as found in a study on rats.
Certain types of learning are not affected by lesions at the hippocampus i. e. nondeclarative or implicit behaviour. Some skills are gradually acquired by training or new learning.
Gradually acquired skills are possible over several learning sessions. Repetition priming tasks are also possible.ECT has an effect on the hippocampus. It gives rise temporarily to a retrograde amnesia for events and materials before the ECT. Some rats who showed retrograde amnesia for the spatial context of tone shock association showed no retrograde amnesia for simple tone shock association.
This same dissociation is seen in anterograde amnesia too. Some studies have shown simple dual store interpretation. Decay of hippocampal memory is rapid. The mammalian brain exploits new or complementary learning systems. Adaptive learning occurs in the neocortex which is formed by the perirhinal and perihippocampal areas.Persistent and repeated attempts at learning facilitate the changes in the synaptic connections in the neocortex.
Newly acquired skills would be evident after a very long time. Information is carried between the neocortex and the hippocampus through bidirectional pathways that translate activity at the neocortex into corresponding activity at the hippocampus. It is not believed to be a direct copy but a re-representation. Reinstatement of the stored event would allow the stored information to be used for controlling behavioural responses. Reinstatement also permits memories initially dependent on the hippocampus to become independent of it.Semantic, episodic and encyclopaedic memory tasks may be taken over by the neocortical system.
Third Study (Kiran and Thompson, 2003 The third study at the University of Texas at Austin had 4 kinds of participants: normal young, elderly, Broca’s aphasic and Wernicke’s aphasic participants. Targets used were typical animate ones. Inanimate ones were the atypical targets. The participants were to identify these targets. Reaction time to judge between the typical and atypical ones was measured. All the four groups made more mistakes for the atypical ones.
However a slight difference in performance was noticed. The first 3 groups comprising of the young, elderly and Broca’s aphasic patients showed similar results for the verification task. Wernicke’s aphasic patients made the most errors on this task and were the slowest. The patients were all seated at a computer. Previous studies have shown that patients with left hemisphere insult showed less positive results than the patients with right hemisphere injury. Grossman had tested the typicality model of semantic organisation on fluent and non-fluent aphasic patients and right hemisphere damaged persons.
Grober et al tested the differences seen with anterior (nonfluent) and posterior (fluent) and a control group. The normal controls were the fastest to respond and the anterior group slowest. Typical items were responded to fastest by all 3 groups. Kiran et al selected 7 Broca’s aphasic and 7 Wernicke’s aphasic patients.
Aphasia was measured using Western Aphasia Battery. Nine each of normal young and normal elderly were also selected with no cognitive impairment, with normal vision or corrected to normal vision, normal hearing and with high school education. All were right handed except for one.Auditory comprehension of simple commands were assessed by the WAB Auditory Comprehension Test. Wernicke’s aphasic had greater difficulty in comprehension than Broca’s aphasic. In the Boston naming test, both these groups showed a variation range which could not give a conclusion.
Semantic processing using selected tests from Psycholinguistic Assessment of Language Processing. Broca’s aphasic patients were superior in word to picture matching test, synonym judgement task and the accuracy at the semantic associate pairs test. All patients were able to read and comprehend single words.The normal young and elderly showed almost no variations in their responses.
The findings indicated that the young and elderly participants were faster at accepting typical examples and rejecting nonmembers compared to accepting atypical examples. Broca’s aphasic patients accepted typical members faster than the atypical ones and rejected non members faster, unlike the controls. Wernicke’s aphasic patients though more accurate, were not faster at accepting typical members or atypical ones or rejecting non members , made more errors, had slower reaction times and had the smallest typicality effect.All the studies speak of the complexity of the brain and its connections and how much it controls our daily activities. Only when some part is injured or has a pathological lesion and when some of our normal habits get impaired do we realise that everything was happening due to the greatest computer that God has presented us. Relearning to speak or reviving our memory with an impaired brain is positively difficult.
Plenty of effort and support are involved in the process.
