Development of vestibulo-ocular responses in visually deprived kittens

The vestibular system contributes to the stabilisation of visual images on the retina by means of vestibulo-ocular compensatory reactions. The development of vestibular control of eye movements has been studied in twelve week old kittens, reared in total darkness, which have been compared with a control group of kittens reared in normal conditions. Postrotatory nystagmus, nystagmus during sinusoidal oscillations, visual suppression of vestibular nystagmus by fixation and pathological mystagmus following hemilabyrinthectomy, have been used as indicators of the functional state of the vestibulo-ocular control system. The results shown that most of the essential features of this control are present in dark-reared kittens. However, differences have been noted which possibly concern precise regulation of compensatory movements and head-eye coordination. The frequency of vestibular nystagmus is much smaller and the initial deviation of post-rotatory nystagmus in the direction of the change of movement is weak or absent in dark-reared kittens. Habituation also seems to operate differently in the two groups of kittens. Visual suppression of vestibular nystagmus is present, however, showing that an important part of the neuronal basis for visual-vestibular interaction has developed.     

Column spacing in normal and visually deprived monkeys

 A recent model for the development of the pattern of eye-dominance domains in primary visual cortex predicts that stimulus conditions during early visual life determine the spacing (or periodicity) of ocular dominance columns (ODC). The model predicts that normal binocular visual experience consists of highly correlated binocular stimulation and leads to relatively narrow ODC spacing, while abnormal binocular visual stimulation attendant with strabismus consists of non-correlated, incoherent, and asynchronous stimulation and leads to wider than normal ODC spacing. Evidence in support of the model has been presented for strabismus in the kitten. We tested the predictions of the model in normal monkeys and others subjected to various forms of abnormal visual experience during infancy. We identified and measured the inter-column spacing (or periodicity) in the V1 cortex of 19 adult monkeys (M. mulatta) using the cytochrome-oxidase (CO) histochemical method. There were no significant differences in the V1 inter-column spacing between normal adult monkeys (n=5) and other adult monkeys having had monocular-form deprivation (n=5), experimental anisometropia (n=5), or experimental strabismus (n=4) early in life. The quality of early binocular visual experience is not a significant determinant of the inter-column spacing in primate V1 cortex. Therefore, the model predicting an increase in the ODC periodicity with strabismus is not supported. Received: 4 December 1997 / Accepted: 12 May 1998     

Adaptation to visual feedback delays in manual tracking: evidence against the Smith Predictor model of human visually guided action

We report adaptation to delayed visual feedback during a manual tracking task, testing the nature of the adapted responses with frequency analysis. Two groups of seven subjects tracked unpredictable targets using a handheld joystick, alternating between pursuit and compensatory display trials. The test group then practised for 1 h per day with a visual feedback delay of 300 ms; the control group practice under normal undelayed conditions. Introduction of the visual feedback delay significantly disrupted tracking performance, with an increase in errors and a reduction in frequency of corrective movements. Subjects showed clear evidence of adaptation during the 5 day experiment, decreasing tracking error and decreasing the mean power of intermittent corrections. However, there was no evidence of a return towards the initial high frequency intermittent tracking. We suggest that the adaptation observed in this study reflects the modification of predictive feedforward actions, but that these data do not support control based on Smith Prediction.     

Multiple periods of functional ocular dominance plasticity in mouse visual cortex

The precise period when experience shapes neural circuits in the mouse visual system is unknown. We used Arc induction to monitor the functional pattern of ipsilateral eye representation in cortex during normal development and after visual deprivation. After monocular deprivation during the critical period, Arc induction reflects ocular dominance (OD) shifts within the binocular zone. Arc induction also reports faithfully expected OD shifts in cat. Shifts towards the open eye and weakening of the deprived eye were seen in layer 4 after the critical period ends and also before it begins. These shifts include an unexpected spatial expansion of Arc induction into the monocular zone. However, this plasticity is not present in adult layer 6. Thus, functionally assessed OD can be altered in cortex by ocular imbalances substantially earlier and far later than expected.     

Functional development of the visual system in normal and protein deprived rats

During an investigation focused on development of visual evoked responses (VER) in normal and protein deprived rats indications of persisting latency differences were found. Since such differences are in variance with previous reports special attention was paid to compare control and protein deprived adult rats. Protein deprivation was induced by feeding rats a diet with 50% reduction in protein content compared with control rat diet from two weeks before onset of gestation until examination. Dependence on experimental variables of latencies and complexity of the VER illustrated the need of a well defined experimental situation. Adult protein deprived rats showed significantly longer latencies to onset and to the first three peaks of the VER and an altered complexity of the response. It is suggested that the observed alterations result from effects of the protein deprivation on early brain development since this and previous studies have shown similar alterations in developing young rats. The divergence in findings between the present and previous reports may be explained by differences in degree of malnutrition and in other experimental conditions.     

Multiple spatial-frequency tuning of electrical responses from human visual cortex

Summary Human occipital potentials evoked by stimulation with a counterphase flickering grating were recorded by a digital narrowband filter technique. The data showed a surprising degree of narrow tuning to particular spatial frequencies in addition to the expected narrow temporal frequency tuning. At each temporal frequency, there could be two or more peaks of response to different spatial frequencies, each distinct from the whole field flicker response. Variations in this multiple spatial frequency tuning were investigated as a function of luminance, electrode location, and temporal frequency for several observers. The results are interpreted in terms of many stimulus-specific resonant neural circuits within the brain, and suggest that it is possible to make a highly detailed exploration of the responses of neural circuits to visual stimulation.Supported by NIH Grants No. 5 R01 EY01582, No. 1 R01 EY02124, NIH General Research Grant No. 5 S01 RR05566 and The Smith-Kettlewell Eye Research Foundation     

Functional development of the visual system in normal and protein deprived rats. III: Recordings from adult optic nerve in vitro

A persistent increase in the latencies of the visual evoked response recorded from the cortical surface of protein deprived adult rats was described recently (Sj?str?m et al. 1984). The morphological correlate to this alteration is unknown. Previous studies on malnourished rats have shown a reduction of axonal diameters and in the number of myelin lamellae in relation to axonal circumference, and hence the possibility of a decrease in fibre conduction velocity must be considered. In parallel study, we have established that changes in diameters and myelination of optic nerve fibres similar to those previously reported in malnourished rats are present in adult protein deprived (PD) rats (Conradi et al. 1985). In the present paper, recordings of optic nerves in vitro from adult normal (C) and protein deprived (PD) rats are described. The compound action potentials were very similar in the two groups. Three positive peaks were easily defined, probably corresponding to three functional groups of optic nerve fibers. No significant differences in amplitudes or conduction velocities for the three peaks were found between the C and PD rats. It is concluded that the increased latencies of the evoked response are not caused by a decrease in conduction velocity.     

Functional development of the visual system in normal and protein deprived rats. Ill: Recordings from adult optic nerve in vitro

SJÖSTRÖM, A., CONRADI, N.G., GUSTAFSSON, B. & WIGSTROM, H. 1985. Functional development of the visual system in normal and protein deprived rats. III: Recordings from adult optic nerve in vitro. Acta Physiol Scand, 125 , 353–358. Received 8 March 1985, accepted 20 April 1985. ISSN 0001–6772. Departments of Physiology and Pathology, University of Goteborg, Sweden. A persistent increase in the latencies of the visual evoked response recorded from the cortical surface of protein deprived adult rats was described recently (SJÖSTRÖM et al. 1984). The morphological correlate to this alteration is unknown. Previous studies on malnourished rats have shown a reduction of axonal diameters and in the number of myelin lamellae in relation to axonal circumference, and hence the possibility of a decrease in fibre conduction velocity must be considered. In parallel study, we have established that changes in diameters and myelination of optic nerve fibres similar to those previously reported in malnourished rats are present in adult protein deprived (PD) rats (Conradi el al. 1985). In the present paper, recordings of optic nerves in vitro from adult normal (C) and protein deprived (PD) rats are described. The compound action potentials were very similar in the two groups. Three positive peaks were easily defined probably corresponding to three functional groups of optic nerve fibers. No significant differences in amplitudes or conduction velocities for the three peaks were found between the C and PD rats. It is concluded that the increased latencies of the evoked response are not caused by a decrease in conduction velocity.     

Development of the air righting reflex in cats visually deprived since birth

Summary Classical experiments on the ability of cats to turn in the air during a free fall, the air righting reflex, have shown that vestibular and visual cues can play a role in this behavior. The development of this air righting reflex in kittens blinded since birth has been studied. The results show that the development in the blinded kittens is the same as in normal kittens with vision: mature by 33 days. This result and the comparison with other studies confirm that the air righting reflex is primarily a vestibular controlled reaction.     

Cross-modal plasticity for the spatial processing of sounds in visually deprived subjects

Until only a few decades ago, researchers still considered sensory cortices to be fixed or “hardwired,” with specific cortical regions solely dedicated to the processing of selective sensory inputs. But recent evidences have shown that the brain can rewire itself, showing an impressive range of cross-modal plasticity. Visual deprivation is one of the rare human models that allow us to explore the role of experience-dependent plasticity of a sensory cortex deprived of its natural inputs. The objective of this paper is to describe recent results regarding the spatial processing of sounds in blind subjects. These studies suggest that blind individuals may demonstrate exceptional abilities in auditory spatial processing and that such enhanced performances may be intrinsically linked to the recruitment of occipital areas deprived of their normal visual inputs. Such results highlight the brain’s remarkable ability to rewire its components to compensate for the challenging neurological condition that is visual deprivation. Moreover, we shall discuss that such cross-modal recruitment may, to some extent, follow organizational principles similar to the functional topography of the region observed in the sighted. Even if such recruitment is especially present in individuals having lost their sight in early infancy, occipital regions also show impressive plastic properties when vision is lost at a later age. This observation will be related to recent results demonstrating that occipital regions play a more important role than previously expected in the spatial processing of sounds, even in sighted subjects. Putative physiological mechanisms underlying such cross-modal recruitment will then be discussed. All these results have important implications for understanding the role of visual experience in shaping the development of occipital regions and may guide the implementation of rehabilitative methods such as sensory substitution or neural implants.

On the functionality of the visually deprived occipital cortex in early blind persons

In early blind mammals, the deprived visual cortex undergoes anatomical and functional alterations. Its functional role was investigated in the early human blind by using patterns of cortical activation as measured by scalp-recorded event-related slow negative DC potential shifts. The blind showed higher occipital negativity than did sighted persons both during a tactile reading task and a non-reading tactile control task. Results point to a possible role for the blind's visual cortex in tactile processes.     

Visual cortical activity during tactile perception in the sighted and the visually deprived

This article reviews studies demonstrating activity in visual cortex during tactile perception in sighted participants as well as in those who have experienced visual deprivation of varying duration. This field has been very active over the last few years, with the result that a number of exciting findings have emerged, but a unifying framework is still lacking. The first section of this article deals with investigations revealing that visual cortical activity is regularly associated with the neural processing of tactile inputs in normally sighted individuals. Next, the possible reasons underlying such visual cortical recruitment are considered. The focus then shifts to the effects of visual deprivation, examining the involvement of visual cortex in sensory and language processing in the early and late blind. The final section gives an account of studies suggesting that a remarkable degree of plasticity can be observed even after quite short-lasting visual deprivation. Overall, it appears that the nature of visual cortical activity during nonvisual tasks in the sighted can be influenced by late-onset blindness and even by brief interruptions of visual input; however, the relevant neural plasticity seems to considerably more exuberant if vision is lost very early in life or was never present, which suggests that there is a critical period for the maximal expression of such plasticity.     

The use of visual feedback is independent of visual awareness: evidence from visual extinction

Milner and Goodale (The visual brain in action, Oxford Press, 1995) made a distinction between vision for perception and vision for action. In contrast to perception, many action tasks have strict temporal constraints, which can only be met if the visual information is relayed directly to the motor system without first passing through a conscious decision making process. Milner and Goodale therefore predict that visual stimuli do not have to reach visual awareness in order to guide rapid motor responses. Online visual feedback provides a good example of visual information that is used under tight temporal constraints to guide rapid motor responses. Online visual feedback provides information about the position of the moving limb. This information can be used to improve the accuracy of our movements. If vision for action operates independently of visual awareness, visual feedback should be beneficial even if the subject is unaware of this information. We tested this prediction in a patient (V.E.) with left-sided visual extinction, a condition in which a visual stimulus typically fails to reach awareness if a second stimulus is presented simultaneously at a more rightward location. V.E. was asked to point towards a central target with his left hand. In some trials a light-emitting diode (LED) provided brief visual feedback from the moving hand. However, in the majority of trials, V.E. was unaware of this LED, due to his extinction. His performance was nevertheless significantly better when visual feedback was present, regardless of whether or not the information was available for verbal report. We conclude that visual awareness is not essential for the effective use of online visual feedback. The study was carried out at: Cognitive Neuroscience Research Unit (CNRU), Wolfson Research Institute, University of Durham, UK     

Paired-pulse behavior of visually evoked potentials recorded in human visual cortex using patterned paired-pulse stimulation

Paired-pulse stimulation techniques are used as common tools to investigate cortical excitability and cortical plastic changes. Similar to investigations in the somatosensory and motor system here we applied a new paired-pulse paradigm to study the paired-pulse behavior of visually evoked potentials (VEPs) in 25 healthy subjects. VEPs were recorded and the responses to the first and the second P100 peak were analyzed at different SOAs [stimulus onset asynchrony (SOA) = interstimulus interval (ISI) + pulse duration (13 ms)]. Two measures describe the paired pulse interaction: the “amplitude ratio”, the ratio of the second to the first amplitude, and the “latency shift”, the difference of the inter-peak interval between the P100 peaks and the respective SOA. To separate alterations in the amplitude of the second VEP response due to changes in paired-pulse inhibition from those originating from superposition of the two waveforms, particularly at short SOAs, we created a waveform template from recordings made at SOAs of 1 s, where interaction can be assumed to be negligible. Superposed traces of VEP recordings were then created by adding two templates at delays corresponding to the SOAs used. The original recordings were then digitally subtracted from the traces obtained by superposition. Analysis of the subtracted traces revealed evidence that at short SOAs the second VEP response is substantially suppressed, a finding comparable to the paired-pulse inhibition described for motor and somatosensory cortex following paired-pulse stimulation. However, paired-pulse inhibition seen in V1 varied considerably from subject to subject, both in respect to amplitude, and to time of maximal inhibition. We found paired-pulse inhibition ranging from 12 to 76% (mean 34%) at SOAs between 80 (shortest discriminable SOA) and 320 ms (mean 128 ms). At intermediate SOAs between 80 and 720 ms (mean 215 ms) the amplitude ratios were between 94 and 145% (mean 116%) indicative of slight paired-pulse facilitation. Comparable to recovery studies by means of paired-pulse median nerve stimulation in somatosensory cortex, at shorter SOAs we found a delayed second VEP response. Combined together, our findings suggest that VEPs are characterized by significant paired-pulse inhibition at short SOAs, a phenomenon reminiscent of findings reported in other modalities. Possible mechanisms and pharmacological properties of the described paired-pulse behavior in visual cortex remain to be explored.     

Sleep‐deprivation and autobiographical memory: evidence from sleep‐deprived nurses

Negative effects of sleep deprivation on different types of memory are well documented, but the specific effects on autobiographical memory performance are not well studied. In this study, we investigated performance on the autobiographical memory test in a group of sleep‐deprived and well‐rested nurses. One‐hundred participants divided into sleep‐deprived (N = 50, 25 females) and well‐rested (N = 50, 25 females) groups took part in the study. The sleep‐deprived group included night‐shift nurses with 8–12 hr sleep deprivation, while the well‐rested group had the usual night sleep before performance assessment. All participants were matched for gender, age, education and employment status. They completed depression and anxiety inventories, and underwent the autobiographical memory test, which included 18 cue words with positive, negative and neutral valence. The sleep‐deprived group scored significantly higher in depression scores. Analysis of covariance (ANCOVA) results showed that sleep‐deprived participants had a significantly poorer autobiographical memory compared with the well‐rested group. Additionally, specific memories were significantly declined in the sleep‐deprived group. This group remembered significantly less positive and more negative memories. Findings implicate that sleep deprivation has detrimental effects on autobiographical memory specificity and valence, and is associated with mood dysregulation.     

The development of visual object recognition in school-age children

This study documents the age-dependent development of visual object recognition abilities in 115 children aged 6 to 11 years, using a battery of neuropsychological tests based on Marr's model (Efron test, Warrington's Figure-Ground Test, Street Completion Test, Poppelreuter-Ghent Test, a selection of stimuli from the Birmingham Object Recognition Battery, a series of color photographs of objects presented from unusual perspectives or illuminated in unusual ways). The results suggest a maturation of complex visual perceptual abilities, possibly related to the development of the cerebral processes involved in object recognition, and could be the starting point for future investigations of these skills in impaired populations.     

Nonlinear responses of simple cells to Mach band stimuli: evidence from early monocularly deprived cats

We have previously shown that, cat simple cells respond linearly to edges of variable blur widths: cells with receptive fields (RFs) of even symmetry respond better to a luminance ramp (where Mach bands are observed); cells with RFs of odd symmetry respond better to a luminance step (where no Mach bands are perceived). Our evidence has also indicated the existence of inhibitory interaction between cells with RFs of even and odd symmetry as predicted by the Tolhurst-Ratliff Mach band model. Since monocular deprivation is known to impair cortical inhibitory mechanisms, we studied the responses of simple cells of adult cats monocularly deprived at the age of 8–10 weeks to Mach band stimuli in order to delineate specific changes in inhibitory interactions caused by monocular deprivation. In pattern-deprived cats, particularly for cells driven by the deprived eye, there were many cells that responded contrary to linear models: odd-symmetric cells responded maximally to blurred edges while even symmetric cells responded maximally to sharp edges. Cells that responded maximally as predicted, responded, similarly to normal cat cells, less than expected at suboptimal widths. All cells in normal and light-deprived cats responded in a linear fashion to sinusoidal stimuli. We conclude, therefore, that intracortical inhibition shapes simple cells' responses to edges. Monocular deprivation impairs this mechanism, thus causing simple cells in monocularly deprived cats to respond nonlinearly to edges. All simple cells responded linearly to gratings since it is not the linear spatiotemporal RF of these simple cells that was impaired under monocular deprivation.