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Cortical correlates of impaired reading in dyslexia
Abstracts /International Journal of Psychophysiology 25 (1997) 17-84
addicts showed more aberrent eating behaviors and attitudes than controls and were also significantly more depressed. Thus, addicts were found to differ from controls, not only in subjective craving for chocolate, but also in physiology, overt behavior and psychopathology.
ENHANCEMENTS OF SYNAPTIC TRANSMISSION, LTP AND MEMORY BY PHARMACOLOGICAL AGENTS
J. SirviG*, M. Pitklnen, R. Pussinen, A. Haapalinna=, P.J. Riekkinen Sr. A.I. Virtanen Institute, Department of Neurology, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Orion-Farmos Corporationa, Turku, Finland
Long-term potentiation (LTP) refers to the long-lasting enhancement of synaptic efficacy by high frequency stimulation of excitatory connections in the brain, e.g., in the hippocampus. While the definitive proof is still lacking, several lines of evidence support the content of LTP as a synaptic substrate for certain forms of learning and memory, e.g., spatial memory. One of those includes evidence that a pharmacological agent (a positive modulator of glutamatergic AMPA receptors) which facilitates the induction of LTP improves learning and memory in rats (Staubli, Perez, Xu, Rogers, Ingvar, Stone-Elander and Lynch, PNAS, 91, 1994). However, the enhancement of synaptic transmission per se can also be relevant for the improvement of memory, especially if the effect of a drug on synaptic transmission is amplified through polysynaptic network (Sit%, Larson, Quach, Rogers and Lynch, Neuroscience, 1996) and the task involves well-learned cues which are pertinent to task demands (Larson, Lieu, Petchpradub, LeDuc, Ngo, Rogers and Lynch. J Neurosci, 15(12), 1995; Granger, Deadwyler, Davis, Moskovitz, Rogers and Lynch, Synapse, 1996). This presentation will discuss two sets of experiments showing that a pharmacological agent (D-CyClOSeIine, a partial agonist at the glycine site of Nmethyl-D-aspartate receptor or atipamezole, an antagonist of alpha-2 adrenoceptors) which facilitates synaptic transmission (an increase in the size of population spike relative to the slope of excitatory postsynaptic potential) in the dentate gyms can enhance the intermediate-term retention of radial arm maze task (in a very familiar environment) in rats. The enhancements by atipamezole which is known to increase the release of noradrenaline in the brain could be related to the modulation of coming visual (and auditory as well as olfactoty) stimuli to the hippocampus facilitating ‘noticing’. This could promote the attention of rats to the pertinent cues during the sampling phase of the radial arm maze task improving their retention of this task few hours later. These data could be relevant for the development of pharmacological treatment for memory disorders.
39
CORTICAL CORRELATES OF IMPAIRED READING IN DYSLEXIA R. Salmelin *l, E. Service*, P. Kiesill, K. Uutela and 0. Salonen ‘Low Temp. Lab., Helsinki Univ. Technology, Espoo, *Dept. Psychology, Univ. Helsinki, Helsinki, 3Dept. Radiology, Helsinki Univ. Central Hospital, Helsinki, Finland Dyslexia is most often attributed to phonological impairments, manifested in abnormal activation of the left temporal and temporo-parietal cortex in response to auditorily presented language. The immediate cortical correlate of the severely impaired reading process in dyslexics has, however, remained obscure. In the present study, we employed whole-head magnetoencephalography (MEG) to characterize the cortical activation sequence during visual word recognition in 6 dyslexic and 8 normal subjects. The subjects were shown 7-8 letter Finnish words and non-words for 300 ms, once every 3 s. We found significant differences between the two groups in three regions: Controls, but not dyslexics, activated the left inferior temporo-occipital cortex within 200 ms after word presentation. This signal likely corresponds to intracranially identified letter-string specific activity in the region of the fusiform gyms. Perception of words as specific units thus seems to be impaired in dyslexics. After 200 ms, activity spread to the left temporal lobe in controls but not in dyslexics, reflecting impaired phonological processing in dyslexia. However, within the time window 200-400 ms, dyslexics but not controls showed activation of the left inferior frontal cortex, implying involvement of Broca’s area. Our results suggest that, in dyslexics, the immediate reason for difficulties with reading is the impaired perception of visual word form. This may result from an initial phonological disorder which would prevent the efficient binding of visual letter strings and spoken entities. PROCESSING SPEED OF THE BRAIN TESTED WITH PERIODIC SIGNALS V. Virsu Dept. Psychology, University of Helsinki, P.O. Box 4 (Fabianinkatu 281, FIN-00014 University of Helsinki, Finland Brain injury, old age and incomplete development slow down or make impossible the performance of a task. A common factor in these conditions is a decrease of temporal accuracy of neuronal signal transfer and a consequent decrease of signal-to-noise ratio (S/N) in the brain processes that control the performance. A method and testing apparatus (CIP, Coherence of Information Processing) for assessing the behavioral indices of S/N of the brain with periodic signals was developed. Trains of signal pairs are used and the subject indicates whether the signal pairs of the trains are detected to be synchronous or asynchronous when the frequency of the pairs varies; the threshold frequency of synchronism is
addicts showed more aberrent eating behaviors and attitudes than controls and were also significantly more depressed. Thus, addicts were found to differ from controls, not only in subjective craving for chocolate, but also in physiology, overt behavior and psychopathology.
ENHANCEMENTS OF SYNAPTIC TRANSMISSION, LTP AND MEMORY BY PHARMACOLOGICAL AGENTS
J. SirviG*, M. Pitklnen, R. Pussinen, A. Haapalinna=, P.J. Riekkinen Sr. A.I. Virtanen Institute, Department of Neurology, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Orion-Farmos Corporationa, Turku, Finland
Long-term potentiation (LTP) refers to the long-lasting enhancement of synaptic efficacy by high frequency stimulation of excitatory connections in the brain, e.g., in the hippocampus. While the definitive proof is still lacking, several lines of evidence support the content of LTP as a synaptic substrate for certain forms of learning and memory, e.g., spatial memory. One of those includes evidence that a pharmacological agent (a positive modulator of glutamatergic AMPA receptors) which facilitates the induction of LTP improves learning and memory in rats (Staubli, Perez, Xu, Rogers, Ingvar, Stone-Elander and Lynch, PNAS, 91, 1994). However, the enhancement of synaptic transmission per se can also be relevant for the improvement of memory, especially if the effect of a drug on synaptic transmission is amplified through polysynaptic network (Sit%, Larson, Quach, Rogers and Lynch, Neuroscience, 1996) and the task involves well-learned cues which are pertinent to task demands (Larson, Lieu, Petchpradub, LeDuc, Ngo, Rogers and Lynch. J Neurosci, 15(12), 1995; Granger, Deadwyler, Davis, Moskovitz, Rogers and Lynch, Synapse, 1996). This presentation will discuss two sets of experiments showing that a pharmacological agent (D-CyClOSeIine, a partial agonist at the glycine site of Nmethyl-D-aspartate receptor or atipamezole, an antagonist of alpha-2 adrenoceptors) which facilitates synaptic transmission (an increase in the size of population spike relative to the slope of excitatory postsynaptic potential) in the dentate gyms can enhance the intermediate-term retention of radial arm maze task (in a very familiar environment) in rats. The enhancements by atipamezole which is known to increase the release of noradrenaline in the brain could be related to the modulation of coming visual (and auditory as well as olfactoty) stimuli to the hippocampus facilitating ‘noticing’. This could promote the attention of rats to the pertinent cues during the sampling phase of the radial arm maze task improving their retention of this task few hours later. These data could be relevant for the development of pharmacological treatment for memory disorders.
39
CORTICAL CORRELATES OF IMPAIRED READING IN DYSLEXIA R. Salmelin *l, E. Service*, P. Kiesill, K. Uutela and 0. Salonen ‘Low Temp. Lab., Helsinki Univ. Technology, Espoo, *Dept. Psychology, Univ. Helsinki, Helsinki, 3Dept. Radiology, Helsinki Univ. Central Hospital, Helsinki, Finland Dyslexia is most often attributed to phonological impairments, manifested in abnormal activation of the left temporal and temporo-parietal cortex in response to auditorily presented language. The immediate cortical correlate of the severely impaired reading process in dyslexics has, however, remained obscure. In the present study, we employed whole-head magnetoencephalography (MEG) to characterize the cortical activation sequence during visual word recognition in 6 dyslexic and 8 normal subjects. The subjects were shown 7-8 letter Finnish words and non-words for 300 ms, once every 3 s. We found significant differences between the two groups in three regions: Controls, but not dyslexics, activated the left inferior temporo-occipital cortex within 200 ms after word presentation. This signal likely corresponds to intracranially identified letter-string specific activity in the region of the fusiform gyms. Perception of words as specific units thus seems to be impaired in dyslexics. After 200 ms, activity spread to the left temporal lobe in controls but not in dyslexics, reflecting impaired phonological processing in dyslexia. However, within the time window 200-400 ms, dyslexics but not controls showed activation of the left inferior frontal cortex, implying involvement of Broca’s area. Our results suggest that, in dyslexics, the immediate reason for difficulties with reading is the impaired perception of visual word form. This may result from an initial phonological disorder which would prevent the efficient binding of visual letter strings and spoken entities. PROCESSING SPEED OF THE BRAIN TESTED WITH PERIODIC SIGNALS V. Virsu Dept. Psychology, University of Helsinki, P.O. Box 4 (Fabianinkatu 281, FIN-00014 University of Helsinki, Finland Brain injury, old age and incomplete development slow down or make impossible the performance of a task. A common factor in these conditions is a decrease of temporal accuracy of neuronal signal transfer and a consequent decrease of signal-to-noise ratio (S/N) in the brain processes that control the performance. A method and testing apparatus (CIP, Coherence of Information Processing) for assessing the behavioral indices of S/N of the brain with periodic signals was developed. Trains of signal pairs are used and the subject indicates whether the signal pairs of the trains are detected to be synchronous or asynchronous when the frequency of the pairs varies; the threshold frequency of synchronism is