Human Occipital Cortex Research Articles

Activation of the human occipital and parietal cortex by pattern and luminance stimuli: neuromagnetic measurements.

We compared cortical reactivity to pattern and luminance stimuli by recording evoked responses and spontaneous brain rhythms from 10 subjects with a whole-scalp neuromagnetometer. Hemifield patterns (black-and-white checkerboards) elicited strong contralateral transient activation of the occipital V1/V2 cortex, maximum at 65-75 ms, followed by sustained activation during the 2 s stimulus. Responses to hemifield luminance stimuli also had an occipital component, but they were dominated by activation of the medial parieto-occipital sulcus (POS) 60-70 ms later. The POS region was equally well activated by foveal and extrafoveal stimuli. The occipital responses to hemifield luminance stimuli differed from those to pattern stimuli in two main aspects: the sustained activation was significantly weaker, and the responses were almost symmetrical, indicating a surprisingly bilateral occipital activation. These effects were similar with foveal and extrafoveal stimuli. The spontaneous 10 Hz alpha rhythm, originating predominantly in the POS region, was suppressed after both stimulus onsets and offsets, more strongly for luminance than pattern stimuli. Activation of the occipital cortex dominated after pattern stimuli, whereas the effect of luminance stimulation was stronger in the parieto-occipital region. The distinct signal distributions in the occipital and POS regions suggest that the two types of stimuli activate the magno- and parvocellular pathways to a varying degree. These findings are also in line with a stronger attention-catching value of the luminance than pattern stimuli.

Generators of visual evoked potentials investigated by dipole tracing in the human occipital cortex

Current source generators (dipoles) of the human visual evoked potentials to pattern-onset stimuli were investigated with the dipole tracing method, using a realistic four-layer head model of scalp-skull-fluid-brain, which can equate the surface potential distributions on a scalp to one or two corresponding equivalent dipoles. Three healthy adult human subjects were used, and 29 electrodes were set on a scalp of each subject. Visual stimulus of a checkerboard pattern was presented for 250 ms in each of eight different visual fields (central and peripheral parts of each of four quadrant fields). The visual evoked potentials consisting of initial positive-late negative waves (CI and CII components designated by Jeffreys and Axford [18]) were recorded mainly on the occipital region contralateral to stimulated visual fields. The initial positive wave (CI) of visual evoked potentials were divided into two components: early component of the CI (e-CI—an early small positive deflection with approximate peak latency of 70–90 ms) and late component of the CI (l-CI—a late large positive deflection with approximate peak latency of 100–120 ms). The dipole with a fit exceeding 98% dipolarity with our model at the shortest latencies was defined as an “earliest dipole” of the evoked potentials, produced by the primary responses in the occipital cortex to an afferent volley from the lateral geniculate body. These earliest dipoles, for eight different visual field stimulations, were estimated at the approximate peak of the e-CI. Estimated dipoles were superimposed on a three-dimensional magnetic resonance image of each subject's brain. Earliest dipoles for right upper and right lower quadrant-field stimulations were located at the left calcarine cortices below and above the calcarine fissure, respectively; earliest dipoles for left upper and left lower quadrant-field stimulations were located at the right calcarine cortices below and above the calcarine fissure, respectively. Furthermore, earliest dipoles for central and peripheral quadrant-field stimulations were located posteriorly and anteriorly in the calcarine cortex, respectively. The results from these non-invasive analyses of visual evoked potentials indicated topographic localization of the dipoles around the calcarine fissure based on the loci of the visual fields. This was comparable to the retinotopy of the human occipital lobe based on clinicopathological studies.

Serum IgA Antibodies from Patients with Coeliac Disease React Strongly with Human Brain Blood-Vessel Structures

Background: Our objective was to determine the possible presence of IgA antibodies directed against human central nervous system (CNS) structures in sera from coeliac disease (CD) patients. Methods: Serum samples were collected from 4 patients with active CD on a gluten-containing diet, 11 biopsy-proven CD patients on a gluten-free diet (GFD), and 52 non-coeliac gastrointestinal controls. In all patients IgA antigliadin antibody (AGA) titres were determined with enzyme-linked immunoassay (ELISA), and IgA antiendomysium antibodies (EMA) with indirect immunofluorescence on human umbilical cord. Cryostat sections of human brain occipital cortex were incubated with the patients' sera and subsequently labelled with anti-human IgA fluorescein conjugate. Results: All sera from patients with active CD on a gluten-containing diet yielded positive results in both the IgG-AGA and EMA test and in indirect immunofluorescence on brain tissue, disclosing a strong fluorescence over blood-vessels structures. All sera from CD patients on a GFD and from non-coeliac gastrointestinal controls gave a negative result on both the EMA test and the immunofluorescence reaction on human brain. Conclusions: Sera from patients with active CD contain IgA antibodies that react with human brain vessel structures, giving intense fluorescence. These antibodies are not present in sera from coeliac patients on a GFD or non-coeliac controls. This finding might be involved in the abnormal nervous system manifestations frequently described in association with coeliac disease.

Fast and Localized Event-Related Optical Signals (EROS) in the Human Occipital Cortex: Comparisons with the Visual Evoked Potential and fMRI

Localized evoked activity of the human cortex produces fast changes in optical properties that can be detected noninvasively (event-related optical signal, or EROS). In the present study a fast EROS response (latency≈100 ms) elicited in the occipital cortex by visual stimuli showed spatial congruence with fMRI signals and temporal correspondence with VEPs, thus combining subcentimeter spatial localization with subsecond temporal resolution. fMRI signals were recorded from striate and extrastriate cortex. Both areas showed EROS peaks, but at different latencies after stimulation (100 and 200–300 ms, respectively). These results suggest that EROS manifests localized neuronal activity associated with information processing. The temporal resolution and spatial localization of this signal make it a promising tool for studying the time course of activity in localized brain areas and for bridging the gap between electrical and hemodynamic imaging methods.

The kinetic occipital (KO) region in man: an fMRI study

We used functional magnetic resonance imaging to explore, in individual subjects, the properties of the kinetic occipital (KO) region, which previous position emission tomography studies have shown to be involved in the processing of kinetic boundaries. The KO region was significantly activated in 23/25 subjects tested in the subtraction of uniform motion from kinetic gratings. The KO region is genuinely specialized for processing kinetic boundaries since it is significantly more activated by kinetic gratings than by luminance-defined gratings, uniform motion or transparent motion. This leaves only the kinetic boundaries, created by discontinuities in motion direction, as the specific stimulus aspect, activating the KO region. The KO region is anatomically and functionally distinct from areas MT/V5, V3 and V3A. It also has minimal overlap with the lateral occipital (LO) region. The selective activation of the KO region is robust and relatively immune to changes in stimulus size, spatial frequency and type of kinetic boundary. These results strongly argue for the view that the KO region is a new, separate, functional region in human occipital cortex.

Attention and probability effects in the human occipital cortex: an optical imaging study.

A new imaging technique (event-related optical signal, EROS) reveals the time course of neural activity in selected cortical areas of normal human subjects. This technique was used to study the event-related activity in striate and extrastriate occipital areas in an experiment in which spatial selective attention and stimulus probability were manipulated. The results show that attention effects are evident in the initial response in extrastriate cortex (latency < 100 ms), but not in striate cortex, confirming previous modeling effects. They also show that the initial response in striate cortex is modulated by stimulus probability, suggesting the occurrence of pre-attentive memory phenomena in primary visual cortex.

Different cortical activation patterns in blind and sighted humans during encoding and transformation of haptic images.

In this study, we investigated whether the occipital cortex of blind humans is activated during haptic perception and/or transformation of a haptic image. Slow event-related brain potentials were monitored from 18 electrodes in 12 sighted and 15 congenitally blind participants while they were engaged in a haptic mental rotation task. In both groups, slow negative shifts appeared over (a) the frontal cortex at the beginning of each processing episode, (b) the left-central to parietal cortex during encoding and maintaining of a haptic image, and (c) the central to parietal cortex during image transformation. A pronounced slow negative potential over the occipital cortex emerged only in the blind individuals and was time-locked to the processing epochs. Its amplitude increased with the amount of processing load. The slow wave effects observed in the blind individuals could indicate that occipital areas participate in specific, nonvisual functions or they could reflect a coactivation of these areas whenever the activation level of task-specific processing modules located elsewhere in the cortex is raised by nonspecific thalamocortical input.

Effect of photic stimulation on energy metabolism in the human brain measured by 31P-MR spectroscopy.

Effect of photic stimulation (PS) on energy metabolism in the human occipital cortex was examined by using phosphorus-31 magnetic resonance spectroscopy in 9 normal subjects. Phosphocreatine (PCr)/total phosphorus signal peak area ratio significantly decreased from 12.3% to 10.9% during the 12 minutes of PS (P < 0.05). PCr once returned to a normal level after PS (11.9%) but significantly decreased again 12-18 minutes after PS (10.8%; P < 0.05). Intracellular pH increased from 7.08 to 7.16 during PS, although this increase was not significant. These results suggest that functional alteration of energy metabolism in the brain is different from that in muscles.

Object-related activity revealed by functional magnetic resonance imaging in human occipital cortex.

The stages of integration leading from local feature analysis to object recognition were explored in human visual cortex by using the technique of functional magnetic resonance imaging. Here we report evidence for object-related activation. Such activation was located at the lateral-posterior aspect of the occipital lobe, just abutting the posterior aspect of the motion-sensitive area MT/V5, in a region termed the lateral occipital complex (LO). LO showed preferential activation to images of objects, compared to a wide range of texture patterns. This activation was not caused by a global difference in the Fourier spatial frequency content of objects versus texture images, since object images produced enhanced LO activation compared to textures matched in power spectra but randomized in phase. The preferential activation to objects also could not be explained by different patterns of eye movements: similar levels of activation were observed when subjects fixated on the objects and when they scanned the objects with their eyes. Additional manipulations such as spatial frequency filtering and a 4-fold change in visual size did not affect LO activation. These results suggest that the enhanced responses to objects were not a manifestation of low-level visual processing. A striking demonstration that activity in LO is uniquely correlated to object detectability was produced by the "Lincoln" illusion, in which blurring of objects digitized into large blocks paradoxically increases their recognizability. Such blurring led to significant enhancement of LO activation. Despite the preferential activation to objects, LO did not seem to be involved in the final, "semantic," stages of the recognition process. Thus, objects varying widely in their recognizability (e.g., famous faces, common objects, and unfamiliar three-dimensional abstract sculptures) activated it to a similar degree. These results are thus evidence for an intermediate link in the chain of processing stages leading to object recognition in human visual cortex.

Visualizing dopamine and serotonin transporters in the human brain with the potent cocaine analogue [125I]RTI-55: in vitro binding and autoradiographic characterization.

The cocaine analogue RTI-55 was evaluated as a probe for in vitro labeling and localization of dopamine and serotonin transporters after death in the human brain. Kinetic, saturation, and competition binding experiments indicated complex interactions of the radioligand with the identification of multiple recognition sites. In membrane binding assays, the association of [125I]RTI-55 at 25 degrees C to putamen membranes was monophasic. In contrast, dissociation of [125I]RTI-55 occurred in two phases with t1/2 values of 9.4 and 36.5 min, respectively. Saturation analysis of [125I]RTI-55 binding demonstrated two binding sites in the human putamen with KD values of 0.10 +/- 0.02 and 1.81 +/- 0.46 nM. The binding of [125I]RTI-55 was displaced by a wide range of cocaine analogues and monoamine uptake inhibitors. The rank order of potency demonstrated in competition assays with human putamen membranes indicates that the radioligand labels cocaine recognition sites on the dopamine transporter (mazindol > GBR 12909 > GBR 12935 > paroxetine > nisoxetine > desipramine > or = fluoxetine > citalopram). In the human occipital cortex, [125I]RTI-55 recognized multiple binding sites with KD values of 0.02 +/- 0.01 and 4.18 +/- 0.46 nM. The rank order of potency for inhibition of [125I]RTI-55 binding to cerebral cortex membranes (paroxetine > citalopram > GBR 12909 > or = mazindol > or = nisoxetine > benztropine) suggests that [125I]RTI-55 labels the serotonin transporter in the human occipital cortex. Autoradiographic mapping of [125I]RTI-55 revealed very high densities of cocaine recognition sites over areas known to be rich in dopaminergic innervation, including the caudate, putamen, and nucleus accumbens.(ABSTRACT TRUNCATED AT 250 WORDS)

Pattern visual evoked potentials recorded from human occipital cortex with chronic subdural electrodes

Pattern evoked potentials to full- and partial-field stimulation were recorded simultaneously from scalp electrodes and from subdural electrodes located over the temporal and occipital cortex, including electrodes placed over or close to the lower lip of the calcarine fissure. High-amplitude pattern evoked potentials were recorded exclusively from electrodes localized in the vicinity of the calcarine fissure and showed a positive-negative deflection in phase with surface recordings, followed by a second negative peak phase reversed with respect to the major surface positive peak (“P100”). The findings suggest that the initial component is an expression of the afferent volley and that the second component (equivalent of the surface “P100”) is most probably generated as a dipole strictly localized to the visual cortex in close proximity of the calcarine fissure (area 17 and/or area 18).

Increased regional cerebral blood flow in inferior occipital cortex and cerebellum of early blind humans

Cerebral flow indices were measured in 7 early blind and 13 sighted persons twice, during a task of passive and of active touch. In the blind, inferior occipital and cerebellar indices were higher. But they were not significantly modified by the kind of tactile task.

Visual sensations produced by intracortical microstimulation of the human occipital cortex

Visual sensations produced by intracortical microstimulation of the human occipital cortex

Suppression of visual perception by magnetic coil stimulation of human occipital cortex

Magnetic coil (MC) stimulation percutaneously of human occipital cortex was tested on perception of 3 briefly presented, randomly generated alphabetical characters. When the visual stimulus-MC pulse interval was less than 40–60 msec, or more than 120–140 msec, letters were correctly reported; at test intervals of 80–100 msec, a blur or nothing was seen. Shifting the MC location in the transverse and rostro-caudal axes had effects consistent with the topographical representation in visual cortex, but incompatible with an effect on attention or suppression from an eyeblink. The MC pulse probably acts by eliciting IPSPs in visual stimulus.

Visual cortex of an anthropoid ape.

Marg et al.1 recorded activity from an unspecified region of the human occipital cortex but the properties of neurones there were very different from those in cat or monkey striate cortex. Work on man's closest relatives, the apes2, might give a better indication of the way in which visual information is analysed in the human cortex. We had an unusual opportunity to study an old, non-reproductive, female black gibbon (Hylobates concolor, a lesser Asian ape from the forests of south-east Asia). The properties of neurones in striate and pre-striate cortex in this animal suggest that the visual areas of anthropoid apes are similar in their organization to those of monkeys3–5.

Phosphenes produced by electrical stimulation of human occipital cortex, and their application to the development of a prosthesis for the blind.

1. To explore the feasibility of a visual prosthesis for the blind, human visual cortex has been stimulated during a series of surgical procedures on conscious volunteers undergoing other occipital lobe surgery.2. Area no. 17 seems the most effective locus for such stimulation, at least in sighted or recently hemianopic patients.3. Changes in electrode size and configuration, or in stimulus parameters, have little effect on subjective sensation.4. Thresholds do vary depending on parameters, but not electrode size, and these effects have been studied.5. Painful effects are associated with stimulation of the dura, but not of the calcarine artery and associated vessels.6. Stimulation of a single electrode usually produces one phosphene, whose size ranges from tiny punctate sensations like ;a star in the sky' up to a large coin at arm's length. Very large elongated phosphenes, like those seen by Brindley's second patient, have not been reported despite the number of patients, electrodes, and combinations of stimulus parameters tested. These large phosphenes may be an effect of prolonged blindness.7. Stimulation substantially above threshold may produce a second conjugate phosphene, inverted about the horizontal meridian.8. Stimulation of a single electrode may also produce multiple phosphenes with no differential threshold.9. Chromatic effects and/or phosphene flicker may, or may not occur. This can vary from point to point on the same patient.10. Phosphenes fade after 10-15 sec of continuous stimulation.11. All phosphenes move proportionately with voluntary eye movements, within the accuracy of our mapping techniques.12. Brightness modulation can easily be achieved by changing pulse amplitude.13. The position of phosphenes in the visual field corresponds only roughly with expectations based on classical maps showing the projection of the visual field onto the cortex.14. Patients can usually discriminate phosphenes produced by 1 mm(2) electrodes on 3 mm centres, although this seems to be close to the limit of resolution.15. Patterns of up to four phosphenes produced by four electrodes have been recognized. However, a variety of complex interactions have been reported.16. Multiple phosphenes are co-planar, although patients are unable to estimate their distance.17. Phosphenes appear immediately when stimulation is begun, and disappear immediately upon cessation of stimulation.18. Future work must concentrate on blind volunteers to explore possible differences in subjective sensation produced after prolonged blindness, and to explore more complex pattern presentation which requires substantial periods of time with any given patient.

Averaged “after-activity” and the alpha regeneration cycle

1. 1. A series of human volunteer subjects were stimulated by repetitive flash and the visual evoked response was averaged in an attempt to study the relationship between so called after-activity and the alpha rhythm. 2. 2. Data were presented which suggest that after-activity is, in fact, the averaged development of alpha regeneration following flash-induced block. 3. 3. A build-up of averaged response and after-discharge in linear relationship to the number of stimuli was not confirmed, nor was lateralization of this build-up observed. 4. 4. In this study, the after-activity was seen to occur during the course of the long flash and, thus, cannot be considered an “off” response. 5. 5. It is suggested that the after-discharge so well known in animal work is not seen in the human occipital cortex in response to flash, but rather with repetitive stimulation the alpha regeneration cycle is of sufficient stability to result in averaging of its stimulus-locked regeneration.

THE EFFECT OF ARTIFICIALLY RAISED METABOLIC RATE ON THE ELECTRO-ENCEPHALOGRAM OF SCHIZOPHRENIC PATIENTS1

From a study of the ‘10 per second’ (alpha) rhythm from the human occipital cortex in relation to temperature variations, Hoagland (1) pointed out that the frequency of the alpha waves under standard conditions is apparently proportional to the rate of respiration of the brain cells. The direct relationship of the lowering of blood sugar (2) to the alpha frequency is in accord with this view. Santenoise (3) has produced evidence which indicates that the thyroid apparatus is involved in cerebral activity. The present report is concerned with the investigation of this problem by the study of the effects on alpha frequency of elevation of the basal metabolic rate by massive doses of thyroxin. This paper is also part of a larger study, now in progress at the Worcester State Hospital, on the physiological and psychiatric changes in deteriorated schizophrenics by hyperthyroidization and hyperthyroxinization.