Effects on Cognition and Brain Function, Research Paper Example

Damage to the brain from stroke, physical injury, or other causes may result in disruption or complete destruction of language processing and speech. The effects of such damage on language and speech are generally classified as aphasia, while more specific labels are applied to various iterations of aphasia based on the area or areas of the brain that are affected. Wernicke’s aphasia, also known as Receptive aphasia, is associated with damage to the Wernicke’s area of the brain. Differentiated symptoms of aphasia are manifested based on the type and location of brain damage; individuals with Wernicke’s aphasia are unable to understand written or spoken language, though they retain the capacity to produce some of the underlying components of speech. These components include the ability to form sentences and speech that retain many of the fundamental rhythms and structures of normal speech, while lacking the use of correct or appropriate words, grammatical structures, and meaning. This paper examines several studies related to the underlying cognitive abnormalities associated with Wernicke’s aphasia.

A variety of diagnostic and investigative tools are used to examine the areas of the brain that are affected by stroke or other injury. Not all cases of Wernicke’s aphasia present with the same symptoms; while the ability to understand vocalized words and speech are generally lost, some patients with Wernicke’s aphasia retain some capacity to recognize and understand written words (Robson et al; 2014).  In addition to the occasional retention of such capacities in some patients, other speech-related functions associated with different strictures and locales in the brain are maintained in some instances. The use of fMRI to examine the processing of written words in Wernicke’s patients is one technique that researchers have applied to the task of understanding the cognitive functions associated with this form of aphasia. The results of one such study, published in 2014, examined 12 subjects with Wernicke’s aphasia and 12 control subjects using fMRI to “examine how the semantic system is altered after damage to the classical comprehension regions” (Robson et al, 2014).  The researchers determined that the degree to which some subjects retained the capacity to comprehend written words was strongly associated with the activation of the anterior temporal lobes that was more pronounced than that seen in the control subjects.

The researchers note that the comprehension of written words involves multiple areas of the brain, combining the same basic phonological processing that underpins the comprehension of spoken words with the visual-processing structures of the brain. In Wernicke’s aphasia the area most affected is that which is associated with phonological processing, which results in both the complete or near-complete inability to comprehend spoken words and a similar inability to form coherent speech. The use of fMRI in these test subjects offered evidence that those who retained some capacity to recognize written words had an increase in the activity of the anterior temporal lobes. This activity was linked to the visual-processing capacity typically associated with normal semantic processing, resulting in the retention or recovery of written-word recognition.

The complex relationship between visual processing and phonological processing that underpins such recovery is explored more thoroughly in a study published in 2012 by Yee, Blumstein and Sedivy.  This study incorporated an eye-tracking examination with the auditory input of various words. Subjects are shown sets of visual images that include an image associated with a specific word. As the subject hears the word, e.g. “nail,” the eye-tracking system monitors the subject’s eye movements to determine if the eyes fixate on the image of a nail rather than on one or more of the other, non-associated images in the set. The results of the study determined that subjects with higher levels of spoken-word recognition also demonstrated higher levels of association with the correct images (Yee, Blumstein & Sedivy, 2012). According to the researchers, these results indicate that “visual priming” may be useful in helping patients recover some measure of semantic processing (Yee, Blumstein & Sedivy, 2012).

While it is not uncommon for patients with Wernicke’s aphasia who retain or recover some measure of semantic or phonological processing to exhibit atypical activity in other regions of the brain, it is rare for patients to exhibit complete or near-complete recovery of phonological processing. A 2011 case study of subject “M” demonstrated that the subject exhibited a significant level of recovery of phonological processing, while exhibiting a concomitant loss of nonverbal auditory recognition (Saygin, Leech, & Dick; 2011). Subject M suffered “unilateral posterior temporal and parietal damage” as a result of stroke; subsequent recovery of the capacity to understand and produce speech was considered by the researchers to be remarkable (Saygin et al, 2011). What made the case of M even more remarkable was his subsequent auditory agnosia; while he could understand spoken words, M lost the capacity to recognize or identify nonverbal sounds.

In an effort to understand why M’s recovery of auditory processing was manifested in such a unique manner, the researchers utilized fMRI to examine the subject’s brain. The fMRI images showed a combination of damage to the Wernicke’s area and increased activation in the contralateral temporal cortex and the perilesional anterior temporal cortex resulting in strong responses to verbal sounds. The researchers described this activity as a “reorganization of auditory processing” that underpinned the recovery of verbal processing, and noted that this reorganization was unusual (as compared to typical patterns of auditory recovery) in that it did not support an associated recovery of nonverbal processing (Saygin et al, 2011). In addition to the use of fMRI the researchers subjected M to a battery of tests, including audiological examination and behavioral testing, the results of which demonstrated M’s near-complete inability to identify nonverbal sounds. The case study of M demonstrates the unique ways in which the brain can recover some processes that have been initially lost through damage or injury.

While each of these studies examines Wernicke’s aphasia from a different perspective, there are some clear shared implications to be found in them. Foremost among such implications is that patients with Wernicke’s aphasia may potentially recover some degree of semantic processing; such recovery is more likely to be seen in the capacity to recognize written words (subject M was a notable exception to this general rule). Two of these studies support the conclusion that recovery of semantic processing is related at least in part to the development of changes in activity levels of undamaged structures in the brain. The research being done on patients with aphasia makes it clear that at least some level of recovery is possible for some patients, a conclusion with clear implications for researchers in the fields of cognition and neuropsychology.

References

Robson, H., Zahn, R., Keidel, J. L., Binney, R. J., Sage, K. & Ralph, M. A. L. (2014). The anterior temporal lobes support residual comprehension in Wernicke’s aphasia. Brain, 137 (3), pp. 931–943.

Saygin, A. P., Leech, R. & Dick, F. (2010). Nonverbal auditory agnosia with lesion to Wernicke’s area.Neuropsychologia, 48 (1), pp. 107–113.

Yee, E., Blumstein, S. E. & Sedivy, J. C. (2008). Lexical-semantic activation in Broca’s and Wernicke’s aphasia: Evidence from eye movements. Journal Of Cognitive Neuroscience, 20 (4), pp. 592–612.