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.Later, Sigmund Freud coined the term visualagnosia to replace psychic blindness.125 However, psychic blindness contin-ued to be used and was immediately applied by Heinrich Klver and Paul Bucyto describe the behavior of their temporal-lobectomized monkeys.(See chap-ter 5.)The second type of blindness Munk distinguished he called Rindenblind-heit, or cortical blindness. It was total absence of vision and he found that itfollowed complete removal of the occipital cortex in both dogs and monkeys.With his monkeys, Munk realized that complete unilateral occipital lesionsproduce blindness not in the opposite eye but in half of each retina.Presumablythe fact that only half the retinal bers cross in the monkey but about 80 percentof them cross in the dog made this phenomenon of homonymous hemianopsiamuch easier to detect by casual observation in the monkey than in the dog.Asfor Ferrier, Munk had this to say126:In my rst communication on the physiology of the cortex.Idid not say anything about Ferrier s work on the monkey because70 From Imhotep to Hubel and Wieselthere was nothing good to say about it.[Ferrier s] statementsand what followed from them.are worthless and gratuitousconstructions since the operated animals were examined by Mr.Ferrier in quite an insufcient manner.as the experiments shownow I have said at that time rather too little than too much, Mr.Ferrier had not made one correct guess, all his statements haveturned out to be wrong.About this time, Lister described his techniques for aseptic surgery, andsoon after, Ferrier and Yeo used them in a new series of cortical lesions inmonkeys.127 Now the animals could be studied for several months after opera-tion, and Ferrier modied his previous views as to the permanence of theblindness after angular gyrus lesions128:Formerly, I localized the visual centres in the angular gyrus, to theexclusion of the occipital lobes.This being a partial truth is an error.Complete destruction of the angular gyri on both sides causesfor a time total blindness, succeeded by a lasting visual impairmentin both eyes.The only lesion which causes complete and perma-nent blindness is total destruction of the occipital lobes and angulargyri on both sides.Despite this retreat, Ferrier (1886) still insisted that Munk s conclusionson the location of the visual area were entirely erroneous and vitiated bythe occurrence of secondary encephalitis. Ferrier s observations on angulargyrus lesions actually anticipated subsequent work implicating the parietalcortex in visual functions.(See chapter 5.)Now Edward Albert Schfer (1850 1935), professor of physiology atUniversity College, London, and later at Edinburgh, entered the fray.In hisrst experiments, carried out with his student Victor Horsley (coinventor ofthe stereotaxic instrument), they obtained results opposite from those of Ferrier,namely, more eye movements from stimulation of the occipital lobe than theangular gyrus, and much greater visual decits from occipital lesions than from71 Chapter 1angular gyrus ones.129 Then Schfer carried out a series of further experimentswith an American neurologist, Sanger Brown, in which the occipital lesionswere more complete than anybody had made previously (gure 1.23), and theystudied several of the animals in detail for several months.130 They convincinglyshowed that total removal of the occipital lobe produced permanently blindanimals, but only if the lesion extended on the ventral surface into the temporallobe.Angular gyrus involvement, however, was neither necessary nor sufcientto produce such blindness.They also failed, in several monkeys, to conrmFerrier s claim that temporal lesions produce deafness.In explanation of thisdiscrepancy, Schfer suggested that Ferrier s one monkey, indisputably deaf aftera temporal lesion, must have been deaf preoperatively.131 (One of Brown andSchfer s monkeys that retained its hearing after bilateral temporal lobectomywas a precursor to all subsequent work on the temporal lobe and vision, asdiscussed in chapter 5.)Ferrier and Schfer continued to quarrel over whether the occipital lobeor the angular gyrus was the visual area (as well as whether the temporal lobehad an auditory center), both in journals and at various national and interna-tional meetings to which they brought their critical monkeys as demonstrationsand to be examined by special committees.William James in his inuentialPrinciples of Psychology, after complaining of all this internecine warfare, camedown unambiguously for a visual area in the occipital lobes.The battle wasvirtually over by then.Today, the bases for the apparent contradictions between Ferrier andMunk and Schfer in the location of the visual area are understandable.Fromhis descriptions and drawings (gure 1.22), it is clear that Ferrier removed theoccipital lobes by an incision parallel to and about a half an inch or moreposterior to the lunate sulcus.This site was chosen to make sure that the entireangular gyrus, his supposed visual center, was entirely spared.By his estimatesthis would remove at least two thirds of the occipital lobes. Today we knowthat such a lesion would leave intact the representation of about the peripheralthirty degrees of the visual eld in striate cortex and, more important, about a72 From Imhotep to Hubel and WieselFigure 1.23 The occipital lesions that Brown and Schfer (1888) reported tocause blindness in macaques.The lesions include what we now know to be theentire representation of the visual eld in striate cortex, including both the rep-resentation of the fovea on the lateral surface (left, dorsal view) and of the ex-treme periphery in the far anterior of the calcarine sulcus (right, ventral view).few degrees of the entire representation of the lower half of the verticalmeridian as well.132 This is enough residual striate cortex to account for thevisually guided behavior described by Ferrier after his occipital lesions.In contrast, Schfer s occipital lesions included not only all the striatecortex on the lateral surface by making his lobectomy through the oor of thelunate sulcus, but in the only animal totally and permanently blind, the bilaterallesion extended on the ventral surface far enough forward to have included allthe buried striate cortex in the anterior calcarine ssure [ Pobierz całość w formacie PDF ]
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.Later, Sigmund Freud coined the term visualagnosia to replace psychic blindness.125 However, psychic blindness contin-ued to be used and was immediately applied by Heinrich Klver and Paul Bucyto describe the behavior of their temporal-lobectomized monkeys.(See chap-ter 5.)The second type of blindness Munk distinguished he called Rindenblind-heit, or cortical blindness. It was total absence of vision and he found that itfollowed complete removal of the occipital cortex in both dogs and monkeys.With his monkeys, Munk realized that complete unilateral occipital lesionsproduce blindness not in the opposite eye but in half of each retina.Presumablythe fact that only half the retinal bers cross in the monkey but about 80 percentof them cross in the dog made this phenomenon of homonymous hemianopsiamuch easier to detect by casual observation in the monkey than in the dog.Asfor Ferrier, Munk had this to say126:In my rst communication on the physiology of the cortex.Idid not say anything about Ferrier s work on the monkey because70 From Imhotep to Hubel and Wieselthere was nothing good to say about it.[Ferrier s] statementsand what followed from them.are worthless and gratuitousconstructions since the operated animals were examined by Mr.Ferrier in quite an insufcient manner.as the experiments shownow I have said at that time rather too little than too much, Mr.Ferrier had not made one correct guess, all his statements haveturned out to be wrong.About this time, Lister described his techniques for aseptic surgery, andsoon after, Ferrier and Yeo used them in a new series of cortical lesions inmonkeys.127 Now the animals could be studied for several months after opera-tion, and Ferrier modied his previous views as to the permanence of theblindness after angular gyrus lesions128:Formerly, I localized the visual centres in the angular gyrus, to theexclusion of the occipital lobes.This being a partial truth is an error.Complete destruction of the angular gyri on both sides causesfor a time total blindness, succeeded by a lasting visual impairmentin both eyes.The only lesion which causes complete and perma-nent blindness is total destruction of the occipital lobes and angulargyri on both sides.Despite this retreat, Ferrier (1886) still insisted that Munk s conclusionson the location of the visual area were entirely erroneous and vitiated bythe occurrence of secondary encephalitis. Ferrier s observations on angulargyrus lesions actually anticipated subsequent work implicating the parietalcortex in visual functions.(See chapter 5.)Now Edward Albert Schfer (1850 1935), professor of physiology atUniversity College, London, and later at Edinburgh, entered the fray.In hisrst experiments, carried out with his student Victor Horsley (coinventor ofthe stereotaxic instrument), they obtained results opposite from those of Ferrier,namely, more eye movements from stimulation of the occipital lobe than theangular gyrus, and much greater visual decits from occipital lesions than from71 Chapter 1angular gyrus ones.129 Then Schfer carried out a series of further experimentswith an American neurologist, Sanger Brown, in which the occipital lesionswere more complete than anybody had made previously (gure 1.23), and theystudied several of the animals in detail for several months.130 They convincinglyshowed that total removal of the occipital lobe produced permanently blindanimals, but only if the lesion extended on the ventral surface into the temporallobe.Angular gyrus involvement, however, was neither necessary nor sufcientto produce such blindness.They also failed, in several monkeys, to conrmFerrier s claim that temporal lesions produce deafness.In explanation of thisdiscrepancy, Schfer suggested that Ferrier s one monkey, indisputably deaf aftera temporal lesion, must have been deaf preoperatively.131 (One of Brown andSchfer s monkeys that retained its hearing after bilateral temporal lobectomywas a precursor to all subsequent work on the temporal lobe and vision, asdiscussed in chapter 5.)Ferrier and Schfer continued to quarrel over whether the occipital lobeor the angular gyrus was the visual area (as well as whether the temporal lobehad an auditory center), both in journals and at various national and interna-tional meetings to which they brought their critical monkeys as demonstrationsand to be examined by special committees.William James in his inuentialPrinciples of Psychology, after complaining of all this internecine warfare, camedown unambiguously for a visual area in the occipital lobes.The battle wasvirtually over by then.Today, the bases for the apparent contradictions between Ferrier andMunk and Schfer in the location of the visual area are understandable.Fromhis descriptions and drawings (gure 1.22), it is clear that Ferrier removed theoccipital lobes by an incision parallel to and about a half an inch or moreposterior to the lunate sulcus.This site was chosen to make sure that the entireangular gyrus, his supposed visual center, was entirely spared.By his estimatesthis would remove at least two thirds of the occipital lobes. Today we knowthat such a lesion would leave intact the representation of about the peripheralthirty degrees of the visual eld in striate cortex and, more important, about a72 From Imhotep to Hubel and WieselFigure 1.23 The occipital lesions that Brown and Schfer (1888) reported tocause blindness in macaques.The lesions include what we now know to be theentire representation of the visual eld in striate cortex, including both the rep-resentation of the fovea on the lateral surface (left, dorsal view) and of the ex-treme periphery in the far anterior of the calcarine sulcus (right, ventral view).few degrees of the entire representation of the lower half of the verticalmeridian as well.132 This is enough residual striate cortex to account for thevisually guided behavior described by Ferrier after his occipital lesions.In contrast, Schfer s occipital lesions included not only all the striatecortex on the lateral surface by making his lobectomy through the oor of thelunate sulcus, but in the only animal totally and permanently blind, the bilaterallesion extended on the ventral surface far enough forward to have included allthe buried striate cortex in the anterior calcarine ssure [ Pobierz całość w formacie PDF ]