Evidence for a third primary visual area in the telencephalon of the pigeon

The presence of a visual projection area in the caudolateral telencephalon of the pigeon was demonstrated with evoked potentials. Shorter latencies were recorded in this region than in both the classic primary telencephalic visual projection areas, the Wulst and the ectostriatum. The evoked potentials from the caudolateral telencephalon were not due to electronic conduction either of potentials from the underlying tectum or of electroretinograms from the eyes, which border on the telencephalon. Projections from the Wulst and the ectostriatum could also be excluded as sources of the short latency visual evoked potentials from the caudolateral telencephalon. The presence of a third visual projection to the telencephalon in the pigeon is discussed in relation to known visual projections to the telencephalon in other vertebrates.     

Visual system development in the duck embryo

This research investigated the ontogeny of evoked activity in the visual system of the duck embryo. Field potentials were recorded from the optic tectum of Peking ducks (Anas platyrhynchos) after electrical stimulation of the contralateral optic nerve head or photic stimulation of the contralateral eye. Recordings were made in embryos on Day 10 of incubation through hatching. Electrical stimulation elicited negative potentials at the dorsal and ventral surfaces and positive potentials in the depths of the tectum in embryos on Day 11 and later. Polarity reversals occurred within 0.5 mm of the respective surfaces. Potentials were reduced or obliterated when stimulus frequencies were increased to 15 Hz. In older embryos, potentials were more widespread, more complex, larger in amplitude, shorter in latency, and of lower threshold than in younger embryos. These results are consistent with the generation of postsynaptic activity in the optic tectum of ducks on Day 11 of incubation. Responses to photic stimuli appeared much later in development: optic tectum responses on the 21st or 22nd day and electroretinogram on the 23rd day.     

Naloxone effects on the visual evoked potentials recorded from the main and accessory visual pathways of the cat.

1. The effects produced by repetitive i.v. administration of naloxone (1, 2 or 4 mg/kg) on the visual evoked potentials (VEPs) recorded along the main and accessory visual pathways were investigated in a modified "encéphale isolé" cat preparation. 2. Naloxone provoked a progressive amplitude enhancement and latency reduction of some components, depending on the structure analyzed, the dose used and the number of administrations applied. Electroretinogram (ERG) and N1-P1 VEP components of optic chiasm (OCh), lateral geniculate body (LGB) and visual cortex (VC) did not present significant changes. 3. Late-latency components (more than 200 msec) appeared in the VEPs of LGB and VC, mainly when 4 mg/kg were used. 4. Our results suggest that endogenous opioids have a modulatory role in the processing of sensory information at different levels of the visual system.     

Integration of information from both eyes by single neurons of nucleus rotundus, ectostriatum and lateral neostriatum in the zebra finch (Taeniopygia guttata castanotis Gould)

Although the optic nerve in birds crosses completely, visual information from the ipsilateral eye also reaches the ectostriatum, the telencephalic statibon of the tectofugal pathway, by recrossing fibers. These recrossing projections connect the contralateral tectum opticum with the ipsilateral nucleus rotundus, which in turn projects to the ectostriatum. The ectostriatum itself projects to the overlying lateral neostriatum, an area which serves an important role in sexual imprinting. This study shows that contralateral and ipsilateral information converges on single neurons within the nucleus rotundus, the ectostriatal region and the lateral neostriatum. In the three brain areas almost all isolated neurons exhibited responses to contralateral as well as bilateral visual stimuli. The number of neurons responding to ipsilateral stimuli increases from nucleus rotundus to the lateral neostriatum. We did not find any neurons driven exclusively by ipsilateral stimuli. The strength of ipsilateral responses is rather weak within the nucleus rotundus and ectostriatum, but shows a sharp increase in the lateral neostriatum. For most neurons of nucleus rotundus and ectostriatum, an additional ipsilateral stimulus did not significantly affect the response to a contralateral one. In contrast, a strong excitatory effect can be found in the neostriatum. The results are in agreement with previous evoked-potential studies and give new insights on the integration of ipsilateral and contralateral stimuli in zebra finch tectofugal visual pathway.     

Long latency evoked potential components in human slow wave sleep

The wave morphology of long latency (more than 200 msec) components of auditory evoked potentials of healthy human adults was analysed in different slow wave sleep stages and at different electrode positions. The results indicated that the marked negative deflection consisted of 2 distinct components with 300 and 550 msec latency and with central and frontal amplitude maxima, respectively. Very long latency components (N1500 and P1900) were observed with monotonously increasing amplitudes parallel to the deepening of sleep. The contribution of the large amplitude, transient evoked slow waves to the SWS EEG and the general role of information processing in the regulation of sleep are briefly discussed.     

Size-threshold changes after lesions of the visual telencephalon in pigeons

Fifteen pigeons were tested in a psychophysical procedure that determined the limits of their ability to detect differences in the sizes of stimuli. The results indicated that intact pigeons can reliably discriminate an annulus 3.0 mm in diameter from one that is 3.9 mm in diameter. In the first experiment, pigeons with lesions of the ectostriatum that spared the medial 15% were unimpaired in their size-discrimination ability. Those cases in which the lesions involved both the medial and lateral regions of the ectostriatum were greatly impaired. In a second experiment, these findings were replicated. In some cases, the electrode trajectory was varied to rule out possible effects from non-ectostriatal structures. In addition, the second study indicated that destruction of the medial ectostriatum with the lateral regions intact had no measurable effect on size-difference thresholds. The medial region of ectostriatum is part of the termination field of a second tectofugal pathway to the telencephalon. This pathway passes from the optic tectum to nucleus dorsolateralis posterior thalami and then to the neostriatum intermedium, including the medial ectostriatum. An examination of the data of the present experiment and those of other behavioral studies of the ectostriatum suggest that the medial ectostriatum may be involved in the processing of visual information with low spatial-frequency components and the lateral ectostriatum may be processing information about the high-frequency composition of stimuli.     

Deprivation of pattern vision studied by visual evoked potentials in the rat cortex

In the present experiments we studied whether visual pattern deprivation affects the visual evoked potential (VEP) as has been assumed from modification of neuronal structures found in the rat cortex under this condition. The VEP of normal and of monocularly deprived rats is similar in waveform and composed of a small negative component at 40 msec, a large and fast positive wave (270 μV) with a latency of 67 msec and a negative afterpotential of 150 msec latency. The low ratio obtained in normal rats between the amplitudes of contralateral and ipsilateral VEPs (2.7:1) in comparison to the ratio of crossed and uncrossed fibers (15:1) indicates volume conduction interference with neural conduction. Mapping of the visual projection to the contralateral hemisphere in normal rats showed that area 17 was the visually most active region. Visual areas 18 and 18a were only secondary in their respnosiveness. Area 7, althought not considered to be a visual area, exhibited fair responses. The cortical region projected by the ipsilateral input overlapped the contralateral region. The mapping procedure was used to describe the responsiveness of monocularly deprived animals. Considering contralateral responses, area 17 of the normal hemisphere showed higher activity by 27% in comparison with the deprived hemisphere. Ipsilateral responses were similar in both cortices. The contralateral potentials recorded in control animals are higher in amplitude by 41% and their latencies are shorter than those recorded in the deprived animals contralaterally to the nondeprived eye. This may point to suppression of binocular interaction as a result of unilateral visual deprivation. It was concluded from the results in which animals were examined after deprivation of 70–170 days that specific neuronal changes occur due to visual deprivation and correlated with the suppression of the visual evoked potential. These changes differ from the gross processes characterized by neural degeneration since the visual system is still responsive.     

Wulst efferents in the little owl Athene noctua: an investigation of projections to the optic tectum.

The efferent projections from the Wulst were studied in the little owl, Athene noctua, using anterograde migration of wheat-germ-agglutinin conjugated horseradish peroxidase (WGA-HRP). Wulst projections were distributed to telencephalic, diencephalic and mesencephalic targets in a general pattern similar to that previously described in other avian species. Our results on the organization of the Wulst-optic tectum pathway in the little owl reveal well defined and laminarly arranged terminal projections into the superficial tectal layers, with a distribution suggestive of topographical relationships between neurons of origin in the Wulst and termination fields in the optic tectum. In contrast to lateral-eyed birds, the little owl possesses conspicuous contralateral projections to the optic tectum. Ipsilateral and contralateral efferents are restricted to different tectal regions, i.e. ipsilateral projections to the caudo-dorsal and contralateral projections to the rostro-ventral optic tectum. In addition, the anterior and posterior Wulst differentially contribute to the ipsilateral and contralateral projections to the optic tectum. This differential organization of Wulst efferents, as well as the presence of substantial contralateral projections, might be related to the high degree of binocular overlap typical of frontal-eyed birds. At a functional level, electric potentials recorded in the optic tectum and evoked by visual stimulation showed that information from one eye can reach the ipsilateral optic tectum. After Wulst ablation, the amplitude of these potentials was significantly reduced, indicating that Wulst efferents may influence visually-evoked activity in the optic tectum.     

Value of multimodal evoked potentials in the assessment of the neurotoxic effects of carbon disulphide

Central nervous system dysfunction among CS2-exposed workers was studied by measuring short latency SSEPs and VEPs. The examinations were done in 40 men. Chronic CS2 intoxication was diagnosed in 21 of them. Latency of N19, N11, N20 of somatosensory evoked potentials and latency of P100 wave of visual evoked potentials were statistically significant longer in CS2 exposed group in comparison with controls. The amplitude of N20 SSEPs was also significantly higher. Increase of N20 amplitude (33 persons) and elongation of its latency (25 persons) were frequent abnormalities of SSEps. In individual assessment of VEPs, most frequent were: abnormal difference in interocular latency of P100 (26 persons) and elongation of P100 latency (25 persons). In the analysed SSEPs and VEPs parameters there was no significant difference between two clinical groups. The authors conclude that the CS2--neurotoxic effect leads to impairment of the peripheral and central part of the somatosensory pathway, as well as to central dysfunction of the visual pathway.     

Neural correlates of chromostereopsis: An evoked potential study

Chromostereopsis is an illusion of depth arising from colour contrast: ocular chromatic aberrations usually make red appear closer to the viewer than blue. Whereas this phenomenon is widely documented from the optical and psychophysical point of view, its neural correlates have not been investigated. To determine the cortical processing of this colour-based depth effect, visual evoked potentials (VEPs) to contrasts of colour were recorded in 25 subjects. Chromostereopsis was found with the stimuli combining spectra extremes. VEP amplitude but not latency effects were observed to colour depth cues, suggesting an underlying, depth-specific slow negative wave, located using source modelling first in occipito-parietal, parietal, then temporal areas. The component was larger over the right hemisphere consistent with RH dominance in depth processing, likely due to context-dependent top-down modulation. These results demonstrate that the depth illusion obtained from contrast of colour implicates similar cortical areas as classic binocular depth perception.     

A second ascending visual pathway from the optic tectum to the telencephalon in the pigeon (Columba livia)

Previous studies in the pigeon (Karten and Revzin: Brain Res. 2:368-377, '66; Karten and Hodos: J. Comp. Neurol. 140:35-52, '70) have described an ascending tectofugal visual pathway from the optic tectum to the ectostriatum by way of the nucleus rotundus of the thalamus. This present study used anterograde autoradiographic and retrograde horseradish peroxidase pathway-tracing techniques to investigate another ascending tectofugal pathway in the pigeon. Injections of 3H-proline/leucine confirmed a previous report that the optic tectum projects to the nucleus dorsolateralis posterior of the thalamus (DLP). This projection is predominantly ipsilateral and is confined to a large-celled caudal region of the nucleus (DLPc); the rostral region of the nucleus (DLPr) is not tectorecipient. Injections of horseradish peroxidase in DLPc labeled cells predominantly ipsilaterally in layers 8-15 of the optic tectum. Injections of 3H-proline/leucine placed in the DLPc labeled a discrete region of the ipsilateral telencephalon. Similar injections of DLPr labeled a contiguous, but more rostral, region of the neostriatum intermedium. Nissl- and silver-stained material indicated that the region in which DLP terminates is cytoarchitecturally distinct from ventromedial ectostriatal core and belt. Injections of horseradish peroxidase at various locations in the neostriatal DLP terminal field demonstrated a rostrocaudal ordering of the DLP projection upon the neostriatum intermedium. Single-unit recording demonstrated that cells in DLPc respond to whole-field illumination at the same latency as cells in the nucleus rotundus, indicating that the tecto-DLPc-neostriatal pathway transmits visual information to the telencephalon. We suggest that comparable pathways may exist in both reptiles and mammals.     

Impaired parvocellular pathway in dyslexic children

Recent studies report that some children with dyslexia have impaired visual processing, specifically in the fast-processing magnocellular pathway. The objective was to study the effect of varying luminance and temporal and spatial frequency on the latency and amplitude of the visual evoked potentials (VEPs) in normal and dyslexic Egyptian children who speak Arabic (a right-left reading and writing system). VEPs were recorded in 52 dyslexic and 41 normal children in the fourth grade using a black and white checkerboard pattern with different checkerboard sizes and different rates of stimuli at high- and low-contrast media. The peak of the major positive wave component (P100) of each waveform and the trough of the previous major negative wave component were identified, and the peak-to-trough amplitude was measured. The latency and amplitude of VEPs in response to different experimental conditions showed significant shortening of P100 latency under high-contrast media and under low spatial frequency in children with dyslexia compared with normal readers. Furthermore, dyslexia children showed prolonged P100 latency in response to high spatial frequency stimulation compared with the low spatial frequency (P=0.003) and significantly higher N1-P1 amplitude under high-contrast media compared with low-contrast media (P=0.02), whilst no such changes were observed in normal readers. These results are suggestive of deficiency within the parvocellular pathway rather than the magnocellular pathway. As reading apparently places demands primarily on the ability to discriminate fine details, which is to say, on the parvocellular system, we suggested that deficiency in this system, at least in Arabic speaking children, could be a predisposing factor in dyslexia.     

Discrimination of mirror-image stimuli after lesions of the visual system in pigeons

Nine pigeons were trained to perform a simultaneous discrimination task with stimuli that were lateral mirror images, vertical mirror images and nonmirror images. All subjects acquired the discriminations rapidly and at approximately equal rates. Following training, bilateral stereotaxic lesions were made in either the visual wulst or ectostriatum, which are telencephalic components of the thalamofugal and tectofugal visual pathways, respectively. After surgery both groups were retrained to their preoperative performance levels or for a maximum of 140 sessions. The performance of the four subjects that received visual wulst lesions was only mildly and transiently impaired and was equally disrupted on each pattern discrimination. The performance of the five subjects that received ectostriatal lesions, however, was markedly and persistently impaired on all pattern discriminations. The impairment was most severe and sustained on the lateral mirror-image discrimination problem in all subjects. Only three of the five subjects with ectostriatal lesions reached their preoperative performance levels on the lateral mirror-image problem, whereas all subjects returned to their preoperative performance levels on the other problems. Possible reasons for this selective deficit in lateral mirror-image pattern discrimination are discussed in relation to interhemispheric pathways and the relative importance of the thalamofugal and tectofugal visual pathways in birds and in mammals.     

Visual evoked potentials in the detection of subclinical optic toxic effects secondary to ethambutol

In 14 patients with tuberculosis treated with ethambutol hydrochloride, pattern-reversal visual evoked potentials (VEPs) were recorded to monocular, whole-field stimulation before the commencement of treatment and one month and three months subsequently. In six subjects, the VEPs showed changes in the latency and amplitude of the P100 component at the one- or three-month interval. In three cases, the VEP changes reversed after cessation of treatment. In five of the six cases, changes were not associated with a change in visual function, as measured by clinical neuro-ophthalmologic examination. Our findings confirm the usefulness of VEPs in the detection of subclinical optic nerve disease and suggest their use in routine monitoring of ocular function in patients treated with ethambutol.     

Interaction of optic tract and visual wulst impulses on single units of the pigeon's optic tectum.

The influences of visual wulst and optic tract (OTr) stimulation on units recorded from the pigeon's optic tectum (OT) were studied. 127 tectal units were excited with short latency by a single OTr volley. Excitation was followed by a long-lasting inhibition. On 54 of the OTr-excited units, single-shock visual wulst stimulation exerted a long-lasting inhibitory effect. On 34 units, the effect was purely excitatory and, on 28 units, excitation was followed by prolonged inhibition. No effect was exerted by wulst stimulation on 24 units. These results are discussed in terms of convergence of wulst and retinal input on OT neurons, and the role of the integration of visual information from both peripheral and central origins is suggested for the OT neurons.     

Visual evoked potentials in Leber's hereditary optic neuropathy

Pattern-reversal visual evoked potentials (VEPs) were measured serially in two brothers with Leber's hereditary optic neuropathy during the active phase of the disease. VEP latency and configuration were normal prior to the onset of visual symptoms. The earliest abnormalities consisted of either prolongation of VEP latency or unusual VEP morphology characterized by a double positive peak. As visual acuity declined progressively over a period of months, there was a parallel progressive prolongation of VEP latency accompanied by less consistent diminution of VEP amplitude. In two eyes, VEP ultimately could no longer be measured. VEP latency was normal in most of the asymptomatic family members, including the maternal presumptive carrier. These findings suggest that VEP measurements do not distinguish the presymptomatic or carrier states but do permit quantitative assessment of the activity and progression of the disease.     

Localization of the optic tract by using subcortical visual evoked potentials (VEPs) in cats.

OBJECTIVES: This study was aimed to clarify the relationship between the amplitudes of visual evoked near field potentials and distance from the optic tract, and to determine the adequate filter settings to record these potentials from the optic tract separately from the far field potentials. METHODS: The visual evoked near field potentials from the optic tract were consecutively recorded through intracerebral electrodes in 6 cats' brains. Different filter settings were tried and the amplitudes of visual evoked potentials (VEPs) were compared with the distance from the optic tract. RESULTS: The filter settings of 100 Hz to 1 kHz were the best to obtain only the near field potentials separately from the far field potentials. Histological sections revealed that the potentials of the surface of the optic tract showed sudden increase of amplitude, above the 50% of the maximum VEPs amplitudes. CONCLUSIONS: The optic tract can be identified using these methods. These results can be applied to localize the optic tract during such an operative procedure as postero-ventral pallidotomy.     

Participation of the thalamofugal visual pathway in a coarse pattern discrimination task in an open arena

The purpose of this study was to examine the role of the thalamofugal pathway in far-field visual processing. Experiment 1 examined the role of the visual wulst and the ectostriatum in a far-field pattern discrimination task in a large open arena. Control pigeons, pigeons with ectostriatum lesions, and pigeons with wulst lesions were trained to discriminate between four patterns within the arena. Ectostriatum-lesioned pigeons were unimpaired and behaved similar to controls. By contrast, wulst-lesioned pigeons were severely impaired in the pattern discrimination task in the open arena and performed poorer than control pigeons and pigeons with ectostriatum lesions. Statistical analyses of regional contributions to the observed impairment identified the left visual wulst and bilateral hyperstriatum ventrale, which lies outside the wulst, as interesting areas. To ensure that the impairment was not due to a general learning deficit, experiment 2 involved training the pigeons in a pattern discrimination task carried out in an operant chamber, which presumably required use of near-field visual information. Wulst-lesioned pigeons were able to learn the task and performed at a level no different from control pigeons. The results of these experiments support the proposal that the wulst may be important for processing far-field information.     

The development of auditory and visual evoked potentials in early treated phenylketonuric children.

Brain-stem auditory evoked potentials (BAEPs) and flash visual evoked potentials (F-VEPs) were gathered from 8 early treated phenylketonuric (PKU) children in a prospective longitudinal investigation during the 1st to the 12th months after birth. No consistent differences were found in the wave morphology of evoked potentials in PKU children from that of age-matched controls. Studying the latency of some components showed that in BAEPs, wave I latency was similar to control values for the whole year, but that the I-V interpeak mean latency (I-V IPL) was always significantly longer than in controls. In F-VEPs wave N1 latency was significantly longer than in controls only at 1-2 months of age, but returned to control values at 3-4 months (when all children were on dietary therapy) and remained in this range up to the 12th month. The mean latency of the P2 wave of flash VEPs was always significantly longer in PKU children than in controls. These results show that relevant alterations in evoked potentials may be found in PKU children several months after starting dietary therapy. This suggests that information processing in the brain may be impaired for a long time, due to abnormal metabolic conditions between birth and the onset of dietary therapy.     

Visual evoked potentials in Reye's syndrome.

Visual evoked potentials (VEPs) induced by flash stimulation in a child who was recovering from Reye's syndrome with complaints of poor left-eye vision were recorded. Ophthalmological examination disclosed intact visual fields and normal visual acuity. Analysis of VEP's, however, showed a grossly abnormal configuration of wave forms, marked prolongation in latency and reduction in amplitude when the left eye was stimulated. Follow-up observation 3 weeks later showed parallel improvements in VEPs and subjective complaints. Thus, from VEP analysis, it may be possible to detect subtle changes in the visual system that have diagnostic and prognostic value.