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The visual functions of the parietal lobe
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THE VISUAL FUNCTIONS OF THE PARIETAL LOBE MOUNTCASTLE, V.B. Bard Laboratories of Neurophysiology, The Johns Hopkins U n i v e r s i t y , Baltimore, Maryland, USA I t is now well known t h a t the dorsal component of the t r a n s c o r t i c a l l y proj e c t i n g visual system engages the homotypical cortex of the parietal lobe over a multi-staged p r o j e c t i o n , converging there with a weaker c o r t i c a l projection of c o l l i c u l a r o r i g i n . There is evidence from studies in humans and in other p r i mates with c o r t i c a l lesions that t h i s system plays a role in the spatial aspects of visual f u n c t i o n s : in the i d e n t i f i c a t i o n of the location and the spatial rel a t i o n between objects; of the patterns of flow in the visual f i e l d s during l o comotion or head t u r n i n g ; in the detection of objects moving in the periphery of the visual f i e l d s and in the d i r e c t i o n of a t t e n t i o n towards them. The properties of the visual neurons of the i n f e r i o r parietal lobule of the monkey appear appropriate f o r these f u n c t i o n s . They subtend very large receptive f i e l d s that are f r e q u e n t l y symmetrically b i l a t e r a l , and spare the central zone of the visual field.
They are e s p e c i a l l y s e n s i t i v e to movement, over a wide range of v e l o c i -
t i e s (I0-500°/sc). They are markedly d i r e c t i o n a l in nature, and the optimal s t i mulus d i r e c t i o n s d i f f e r lities
in d i f f e r e n t parts of the receptive f i e l d s . Directiona-
are organized so that many neurons respond p r e f e r e n t i a l l y to s t i m u l i mo-
ving inwardly from the periphery towards the central l i n e of gaze, others to outwardly moving s t i m u l i . The mechanisms of d i r e c t i o n a l i t y are of two types. For the f i r s t ,
the radial organization of d i r e c t i o n a l ~ t y depends upon differences
in the local or minute d i r e c t i o n a l i t y
in d i f f e r e n t parts of the receptive f i e l d .
For the second, i t depends upon the past h i s t o r y of the stimulus in the visual field,
f r e q u e n t l y upon i t s passage through remote regions of the f i e l d in which
i t evokes no overt response. For many neurons, both mechanisms operate to create the organization of d i r e c t i o n a l i t i e s .
THE EFFECT OF KAINIC ACID MICROINJECTIONS INTO NUCLEUS RAPHE DORSALIS ON BRAIN EXCITABILITY LEVEL IN CAT MOYANOVA, S., ROUSSEVA, S. AND DIMOV, S. I n s t i t u t e of Physiology, Dept. of Experimental Pharmacology, Bulg. Acad. S c i . , Bulgaria Kainic acid (KA) in doses of 0.2 to 60 nmols dissolved in phosphate b u f f e r (40 n i - I . 2 u l ) was injected into the nucleus raphe d o r s a l i s of cats in order to
THE VISUAL FUNCTIONS OF THE PARIETAL LOBE MOUNTCASTLE, V.B. Bard Laboratories of Neurophysiology, The Johns Hopkins U n i v e r s i t y , Baltimore, Maryland, USA I t is now well known t h a t the dorsal component of the t r a n s c o r t i c a l l y proj e c t i n g visual system engages the homotypical cortex of the parietal lobe over a multi-staged p r o j e c t i o n , converging there with a weaker c o r t i c a l projection of c o l l i c u l a r o r i g i n . There is evidence from studies in humans and in other p r i mates with c o r t i c a l lesions that t h i s system plays a role in the spatial aspects of visual f u n c t i o n s : in the i d e n t i f i c a t i o n of the location and the spatial rel a t i o n between objects; of the patterns of flow in the visual f i e l d s during l o comotion or head t u r n i n g ; in the detection of objects moving in the periphery of the visual f i e l d s and in the d i r e c t i o n of a t t e n t i o n towards them. The properties of the visual neurons of the i n f e r i o r parietal lobule of the monkey appear appropriate f o r these f u n c t i o n s . They subtend very large receptive f i e l d s that are f r e q u e n t l y symmetrically b i l a t e r a l , and spare the central zone of the visual field.
They are e s p e c i a l l y s e n s i t i v e to movement, over a wide range of v e l o c i -
t i e s (I0-500°/sc). They are markedly d i r e c t i o n a l in nature, and the optimal s t i mulus d i r e c t i o n s d i f f e r lities
in d i f f e r e n t parts of the receptive f i e l d s . Directiona-
are organized so that many neurons respond p r e f e r e n t i a l l y to s t i m u l i mo-
ving inwardly from the periphery towards the central l i n e of gaze, others to outwardly moving s t i m u l i . The mechanisms of d i r e c t i o n a l i t y are of two types. For the f i r s t ,
the radial organization of d i r e c t i o n a l ~ t y depends upon differences
in the local or minute d i r e c t i o n a l i t y
in d i f f e r e n t parts of the receptive f i e l d .
For the second, i t depends upon the past h i s t o r y of the stimulus in the visual field,
f r e q u e n t l y upon i t s passage through remote regions of the f i e l d in which
i t evokes no overt response. For many neurons, both mechanisms operate to create the organization of d i r e c t i o n a l i t i e s .
THE EFFECT OF KAINIC ACID MICROINJECTIONS INTO NUCLEUS RAPHE DORSALIS ON BRAIN EXCITABILITY LEVEL IN CAT MOYANOVA, S., ROUSSEVA, S. AND DIMOV, S. I n s t i t u t e of Physiology, Dept. of Experimental Pharmacology, Bulg. Acad. S c i . , Bulgaria Kainic acid (KA) in doses of 0.2 to 60 nmols dissolved in phosphate b u f f e r (40 n i - I . 2 u l ) was injected into the nucleus raphe d o r s a l i s of cats in order to