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Cognitive Neuropsychology and Functional Brain Imaging: Implications for functional and anatomical models of cognition


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Cognitive Neuropsychology and Functional Brain Imaging: Implications for functional and anatomical models of cognition. An introduction to the history of Neuropsychology and the methods that were used in this field over the last decades.

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Cognitive Neuropsychology and Functional Brain Imaging: Implications for functional and anatomical models of cognition

  1. 1. Cognitive Neuropsychology and Functional Brain Imaging: Implications for functional and anatomical models of cognition Humphreys & Price, 2001
  2. 2. Introduction <ul><li>Main aims of Cognitive Neuropsychology </li></ul><ul><li>Use of normal cognition models in order to constrain our understanding of effects of brain lesions on human performance. </li></ul><ul><li>Use data from patients in order to constrain the developments of normal cognition models (i.e. Broca Area). </li></ul><ul><li>Neuropsychological research on patients </li></ul><ul><li>+ </li></ul><ul><li>Research on normal cognition models </li></ul><ul><li>= </li></ul><ul><li>Cognitive Neuropsychology </li></ul>
  3. 3. Introduction <ul><li>What are the benefits of using functional brain imaging techniques? </li></ul><ul><li>More precise than other neuropsychological techniques in terms of localization of the brain areas involved in cognitive tasks </li></ul><ul><li>By choosing the appropriate tasks we can isolate particular cognitive processes and localize their neural activity </li></ul><ul><li>These techniques help us understand the functional components of different cognitive functions </li></ul>
  4. 4. Neuropsychology and cognitive-anatomical models <ul><li>Beginning of the 19 th century: Using of case studies in order to construct normal cognition models </li></ul><ul><li>Building a speech production model </li></ul><ul><li>(1861) Broca's Area: Motor Aspects of Speech </li></ul><ul><li>(1874) Wernicke's Area: Auditory Aspects of Speech </li></ul><ul><li>(1885) Lichtheim: Arculate Fasciculus: connection </li></ul><ul><li>Lichtheim proposed a speech production model </li></ul><ul><li>based on Broca's, Wernicke's and his own </li></ul><ul><li>observations </li></ul><ul><li>Speech Comprehension => Info Transmission => Speech Production </li></ul><ul><li>Wernicke's Area => Arculate Fasciculus => Broca's Area </li></ul>
  5. 5. Neuropsychology and cognitive-anatomical models <ul><li>Speech Comprehension => Info Transmission => Speech Production </li></ul><ul><li>Wernicke's Area => Arcuate Fasciculus => Broca's Area </li></ul><ul><li>(1891) Dejerine complemented this model by observing two different reading disorders: </li></ul><ul><li>Alexia with agraphia (damaged left angular gyrus) </li></ul><ul><li>Patients are not able to recognize and write words </li></ul><ul><li>Alexia without agraphia (left occipital lobe) </li></ul><ul><li>Patients are not able to recognize words BUT they are able to write </li></ul><ul><li>He suggested that Alexia w/o agraphia caused by disconnection of visual areas in the left occipital lobe from the left angular gyrus and so patients can't recognize words. </li></ul>
  6. 6. Neuropsychology and cognitive-anatomical models <ul><li>Early studies tried to answer the question: </li></ul><ul><li>How does a brain lesion affect the cognitive functions? </li></ul><ul><li>1) The lession damages the stored cognitive representations </li></ul><ul><ul><li>Example: Damage in Broca's Area, Damage in Wercnicke's Area </li></ul></ul><ul><li>2) The lession disconnects different representations </li></ul><ul><ul><li>Example: Damage in Arculate Fasciculus </li></ul></ul>Similar References in Neuropsychological studies continue even today!
  7. 7. Problems for Cognitive-Anatomical Models <ul><li>Association </li></ul><ul><li>Accidental Brain Lesions = NO functional boundaries </li></ul><ul><li>We can't infer that all of the affected cognitive processes depend on a common cognitive operation. </li></ul><ul><li>Example: </li></ul><ul><li>Alexia With Agraphia after damage to the left angular gyrus: reading and writing depend on common visual representations for words. </li></ul><ul><li>BUT The same patient may manifest “phonological dyslexia” </li></ul><ul><li>intact access to stored memories of words </li></ul><ul><li>“ surface dysgraphia” </li></ul><ul><li>impaired access to lexical knowledge of spellings </li></ul><ul><li>This dissociation indicates that there are distinct memory representations for writing and reading </li></ul>They can read the word “busy” but they can't spell it. They are impaired at writing irregular but not regular words
  8. 8. Problems for Cognitive-Anatomical Models <ul><li>Interactive effects </li></ul><ul><li>Example : Some patients are able to make semantic categorizations (e.g. separate fruits from vegetables) but they can't name the examples within these categories (e.g. bananas, lettuce) and they have a mild deficit in the perceptual knowledge about objects. </li></ul><ul><li>Question : What's the relation between all these deficits and abilities? </li></ul><ul><li>Answers: 1. They are totally unrelated. Patients have two different deficits/problems: </li></ul><ul><ul><li>2. They are related </li></ul></ul>Sensory Input Semantic Knowledge Object Naming Semantic Knowledge Object Naming Sensory Input
  9. 9. Problems for Cognitive-Anatomical Models <ul><li>Syndromes VS Single Cases </li></ul><ul><li>Often focus on “core symptoms” of syndromes </li></ul><ul><li>BUT there is high heterogeneity between different patients of the same syndrome </li></ul><ul><li>Example : Alexia w/o Agraphia Impairment in early visual coding of letters Impairment in later stages of visual coding </li></ul><ul><li>There is a need to breakdown the tested function and not to be linked to a complex task, otherwise we fail to emphasize the heterogeneity. </li></ul><ul><li>Patient groups need to be differentiated! Emphasis on the dissociations between single cases. </li></ul>Poor transmission from a stored visual word form to other parts of words recognition system
  10. 10. Problems for Cognitive-Anatomical Models <ul><li>Compensatory Strategies </li></ul><ul><li>Often, soon after the lesion, patients develop compensatory strategies to override the normal cognitive process. </li></ul><ul><li>That's why: </li></ul><ul><li>These compensatory strategies do not necessarily reflect the normal cognitive process in normal population </li></ul><ul><li>Sometimes is difficult to detect the original deficit caused by the brain lesion. </li></ul><ul><li>BUT modern techniques provide us the means to try and address the residual cognitive processes </li></ul>
  11. 11. Problems for Cognitive-Anatomical Models Damaging Representations, Disconnections and Sampling Bias 1 2 Some brain regions more vulnerable to damage than others. 3 Some cognitive precesses are represented bilaterally, making their disturbances rare.
  12. 12. Cognitive Neuropsychology <ul><li>C.N. links brain lesions with functional models (not 1to1 relations) </li></ul><ul><li>example : Distributed Associative Memory model </li></ul><ul><ul><ul><li>Functional Level Anatomical Level </li></ul></ul></ul><ul><ul><ul><li>Lesion on these two anatomical units: no “pure” deficits. Functional Interaction between the DAM functional units </li></ul></ul></ul>
  13. 13. Cognitive Neuropsychology <ul><li>Modern Models are more complex, enabling us to explain better the differences between similar deficits </li></ul><ul><li>1890 2000 </li></ul>Components are Functionally Isolable
  14. 14. Cognitive Neuropsychology <ul><li>Data from cognitive neuropsychology studies can be used to argue for the functional necessity of the particular processes of a given task. </li></ul><ul><li>Example : Disorders of semantic knowledge disrupt object naming but not word naming. That means that activation of semantic knowledge is necessary in order to name an object, but not in order to name a word. </li></ul><ul><li>BUT We can't argue about localization of a brain function based on case studies. No generalization is possible. </li></ul><ul><li>There are some constraints in making direct inferences about the functional necessity: a)dependency on associations/dissociations b) hard to distinguish damaged from disconnected brain areas </li></ul>
  15. 15. Functional Imaging: Advantages <ul><li>Better localization / more accurate measurements </li></ul><ul><li>Some lesions tend to occur infrequently. With F.I. We can analyze the cognitive functions related to these areas. </li></ul><ul><li>Not biased studies towards cognitive functions that are commonly affected by neural damage. </li></ul><ul><li>We can analyze and make inferences for the whole brain, not only for the damaged sites. </li></ul>WHERE ==> WHAT ==> MULTIPLE ROLES
  16. 16. Functional Imaging & Cognitive Neuropsychology <ul><li>Using tasks patients can perform </li></ul><ul><li>Important because if we use tasks patients can't perform: </li></ul><ul><ul><li>CASE A : No activation in damaged area, but activation in other areas. </li></ul></ul><ul><ul><li>1) The known damaged area will show no activation. We know that! </li></ul></ul><ul><ul><li>2) The contribution of the activated regions to normal task performance cannot easily be deducted. </li></ul></ul><ul><ul><li>CASE B : Reduced activation in damaged area and in other remote areas. </li></ul></ul><ul><ul><li>1) This could mean that these areas are linked with the to the damaged region </li></ul></ul><ul><ul><li>2) An alternative explanation is that these areas are unrelated to damaged region but they receive the products of the processing in the damaged areas. No output, no input, no activatio. </li></ul></ul>
  17. 17. Functional Imaging & Cognitive Neuropsychology <ul><li>FI can reveal the activity of distant areas </li></ul><ul><ul><li>Example : Patients with damage in Broca's area VS Normal Subjects </li></ul></ul><ul><ul><li>Task : Response to words and consonant strings, containing letter with an ascender (b,d,f,h,g). </li></ul></ul><ul><ul><li>Previous studies showed activation of Broca's area in normal subjects. The aim was to examine how the word processing was affected by the lesion </li></ul></ul><ul><ul><li>Underactivity in left posterior inferior temporal cortex indicates that this region interacts functionally with the Broca's area. </li></ul></ul>
  18. 18. Functional Imaging & Cognitive Neuropsychology <ul><li>Necessary and sufficient brain systems </li></ul><ul><li>FI studies can reveal the necessity and sufficiency in neural level. </li></ul><ul><li>Example : Patients with atrophy of temporal lobes, anterior middle temporal cortices, the anterior cingulate and the right cerebellum and a patient with damage in left inferior frontal cortex were able to perform semantic judgments. </li></ul><ul><li>Conclusion : these areas are not necessary for semantic access </li></ul><ul><li>The remaining areas are sufficient to support the semantic retrieval. </li></ul>
  19. 19. Functional Imaging & Cognitive Neuropsychology <ul><li>Imaging Functional Recovery </li></ul><ul><li>We want to know the functional recovery of patients. </li></ul><ul><ul><li>This may facilitate the development of rehabilitation programmes, especially for patients with common characteristics in terms of recovery. </li></ul></ul><ul><ul><li>This may us understand if patients use alternative strategies or the residual normal processes when they perform a given task. </li></ul></ul><ul><li>Three types of recovery functions: </li></ul><ul><ul><li>peri-infract activation = surrounding neurons support the processing </li></ul></ul><ul><ul><li>neuronal reorganization = the same cognitive architecture uses different neuronal structures </li></ul></ul><ul><ul><li>cognitive reorganization = patient uses a new cognitive strategy </li></ul></ul>