The Journal of Neuroscience, December 1992, fZ(12): 4721-4736 Development of Binocular Vision in the Kitten’s Striate Cortex Ralph D. Freeman and lzumi Ohzawa Group in Neurobiology, School of Optometry, University of California at Berkeley, Berkeley, California 94720 Studies of the development and plasticity of the visual path- factors may be applicable. In any case, although major re- way are well documented, but a basic question remains open: finements occur in stereoscopic vision postnatally, the what is the physiological status of the system prior to ex- physiological connections that underlie this function are tensive visual experience? Somewhat conflicting answers operational at a very early postnatal age. have been put forward, and in a major area, binocular vision, reports have ranged from severe immaturity to well-devel- The development and plasticity of visual function has been oped maturity. This is an important question to resolve since studied extensively by useof behavioral, physiological, anatom- binocular cells in the visual cortex are thought to be the ical, and neurochemical approaches.This work has engendered neural substrate for stereoscopic depth perception. a considerable literature, which is reviewed in several articles We have addressed this question by recording from single (see,e.g., Fregnecand Imbert, 1984; Mitchell and Timney, 1984). cells in the striate cortex of kittens at postnatal ages 2, 3, In order to understand the limits and rules of plasticity, one and 4 weeks and from adults for comparison. Gratings with requires firm knowledge of normal visual functions at various sinusoidal luminance distribution are presented to left, right, stagesof development. By far the most studied animal in this or both eyes. For each cell, we determine optimal values for work is the cat. At birth, a kitten’s eyelids are sealedand optical orientation and spatial frequency. Relative phase (retinal dis- quality of the eye is poor (Thorn et al., 1976; Freemanand Lai, parity) is then varied in a dichoptic sequence so that bin- 1978).However, optical function improves markedly during the ocular interaction may be studied. first few postnatal weeks, and measurementsof retinal image Results are as follows. In the normal adult, we have shown quality suggestthat visual performance is not limited by this in previous work that most binocular interaction in the visual non-neural factor (Bonds and Freeman, 1978). cortex can be accounted for on the basis of linear summa- There is a somewhat surprising paucity of data on develop- tion. Results from 3 and 4 week postnatal kittens are closely ment of peripheral connections in the retina and LGN. Physi- similar to those from adults. All types of binocular interaction ological studiesof the retina of the kitten show that brisk visual found in adults are present in kittens. This includes phase- responsesof ganglion cellsoccur during the third postnatal week specific and non-phase-specific suppression or facilitation. (Hamasaki and Flynn, 1977; Rusoff and Dublin, 1977). How- Furthermore, monocular and binocular tuning characteristics ever, receptive fields are generally large, responsesare weak, and are comparable in kittens and adults. The clear changes that antagonistic surrounds are poorly defined. These same char- occur with age are optimal spatial frequencies and peak acteristics have been observed in the caseof the LGN (Daniels responses. In addition, at 2 weeks, there is a substantially et al., 1978; Ikeda and Tremain, 1978). higher proportion of monocular cells compared to other ages Developmentally, most attention has been paid to the visual and correspondingly, lower relative numbers of cells that cortex. Physiological studies of cortical cells in kittens have exhibit phase-specific or suppressive binocular interactions. resulted in a face-off of Nativist and Empiricist views. The Na- From increases in optimal spatial frequency and interpu- tivist notion is supported by the original work of Hubel and pillary distance with age, we calculated predicted changes Wiesel(l963) who observed, from a small population of cells, in binocular disparity thresholds (stereo acuity) with age. that the main responseproperties found in adult cortex, that is, Although there are methodological limits with respect to the direction and orientation selectivities, and binocularity, were behavioral testing of young kittens, the predicted results are also present in the visually inexperienced cortex of kittens. The comparable to some of the values obtained. Considered to- Empiricist concept is invoked by the reports of Barlow and gether, our results show that the physiological apparatus for Pettigrew (197 1) and Pettigrew (1974), who noted that the cor- binocular vision is functional at an early stage in postnatal tical cells of visually inexperienced kittens did not exhibit stim- development. It is possible that the connections that underlie ulus specificity. Although some subsequentreports suggestpo- this function are developed rapidly during early postnatal sitions betweenthe two extreme views (e.g., Blakemoreand Van experience. An alternative possibility is that there is an elab- Sluyters, 1975; Fregnac and Imbert, 1978; Bonds, 1979; Der- orate genetic organization of binocular vision, but our study rington and Fuchs, 198 l), more recent work tends to support does not address this issue directly. A combination of these the original claim of Hubel and Wiesel (1963) that the major elementsof visual specificity are genetically programmed. They Received Mar. 4, 1992; revised June 16, 1992; acceptedJune 25, 1992. do not begin to deteriorate, in the event of visual deprivation This work was supported by research and CORE grants from the National Eye in the kitten, until 3 or 4 weeks postnatal (Albus and Wolf, Institute (EYOl175 and EY03 176) and by a collaborative project of the Human 1984; Braastad and Heggelund, 1985). However, beyond that Frontier Science Program. Correspondence should be addressed to Ralph D. Freeman, 360 Minor Hall, period, deprivation causesdeterioration of visual processes(see, University of California, Berkeley, CA 94720. e.g., Mitchell and Timney, 1984)and thesemay occur relatively Copyright 0 1992 Society for Neuroscience 0270-6474/92/124721-16$05.00/O quickly (e.g., Freeman et al., 1981; Freeman and Olson, 1982). 4722 Freeman and Ohzawa - Cortical Development of Binocular Vision It is clear. therefore. that normal visual exnerience is reauired comnound (Mizzv Inc.) was used. which is pliable when heated and for proper development of the visual system. hardens upon cooling. We placed the heated material around the skull avoiding the area through which an electrode would be placed. The head In all the studies noted above, the focus of attention has been of a bolt was submerged in the compound and after hardening, it was on monocular properties of cells. Very little attention has been used to secure the head to the stereotaxic frame so that ear bars could paid to the binocular system. An anatomical study of ocular be avoided. For kittens, we used the lamda suture rather than Horsley- dominance columns and their development in layer IV of the Clarke coordinates and performed the craniotomy around a region 4 kitten’s visual cortex suggests that column formation begins mm anterior and 2 mm medial to the suture. Dura mater beneath the craniotomy was reflected and removed. A microelectrode was posi- before 3 weeks of age and is adultlike at about 6 weeks (LeVay tioned at an angle of lo” medial and 5” anterior with the intention of et al., 1978). The only physiological study of the development traversing the medial bank of the postlateral gyms as the electrode was of binocular vision apnears to be that of Pettiarew (1974). He lowered through striate cortex. A 3% agar gel at 38°C was placed around found that binocular disparity selectivity was nearly entirely the electrode, and a sealed chamber was created with melted wax. The animal was placed in front of a tangent screen and given a loading absent in postnatal weeks 2, 3, and 4. Only in the fifth week dose (around 10 mg kg- I) of gallamine triethiodide (Flaxedil) to cause doesit appear and even then, the majority of cells do not exhibit paralysis so that eye movement was minimized. The cat was connected binocular disparity selectivity (Pettigrew, 1974, his Fig. 8). This to a ventilator to provide artificial respiration with a mixture of N,O is a remarkable finding since it suggeststhat development of (70%) and 0, (30%). Paralysis was maintained with Flaxedil infused at binocularity lags considerably behind that of the monocular the rate of 10 mg.kggl.hr-lsl. The Flaxedil is mixed with 5% dextrose or lactated Ringer’s solution (1 and 3 ml.hr-lsl for kittens and adults, system. respectively). Pupils were dilated with atropine (1 o/o), and nictitating To clarify this issue, we have examined quantitatively the membranes were retracted with phenylephrine hydrochloride (10%). development of binocular vision in the kitten’s striate cortex. Contact lenses with 4 mm artificial pupils were placed on each cornea. We use a robust visual stimulation technique that employs large, Temperature was monitored and maintained by use of a feedback- bright gratings whose relative phase between the two eyes is controlled heating pad unit at around 38°C. Intratracheal pressure was monitored with a pressure gauge in the input tube from the respirator. varied to alter retinal disparity. Our results demonstrate that ECG traces and end-tidal CO, levels were also monitored. Expired CO, disparity-selective cells are ascommon in 3 and 4 week postnatal was maintained at around 4.5% by adjusting tidal volume ofthe pump kittens as they are in adults. Even at 2 weeks, a substantial and occasionally by adding CO, to the gas mixture. Light anesthesia number of the cells that could be driven were disparity selective. was maintained by supplementation of the N,O with intravenous in- fusion of Surital(1 mg . kg- I. hr I). Anesthesia was considered sufficient Estimatesof the width of tuning of disparity-selective cells show when pinches of a paw and tactile stimulation of an eyelid elicited no extensive overlap with those for adults.