Transcranial magnetic stimulation (TMS) of early visual but not frontal cortices reveals a feature memory of substantial duration

Objective: How the brain achieves integration of temporally dispersed information is one of the enigmas in the neurosciences. By combining feature fusion with transcranial magnetic stimulation (TMS), we show that individual visual features are stored for several hundred milliseconds before being condensed into a conscious percept. Methods: We presented two verniers with opposite offset directions in rapid succession at the same retinotopic location. Because of the short durations (30ms each) only one fused vernier is perceived. The perceived offset of the fused vernier is a combination of the offsets of the two verniers which themselves are consciously not accessible. We then applied TMS at different times after the onset of the first vernier over the occipital or frontal cortex. Six healthy paid subjects contributed with 120 trials per condition each to the study. Results: When TMS was applied occipitally from 45ms to 95ms after the onset of the first vernier, the second vernier dominated significantly (p

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Michael Herzog, Nicole Lironi, Johannes Rüter, Frank Scharnowski
2008
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https://infoscience.epfl.ch/record/147896?ln=en

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Transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) is a noninvasive form of brain stimulation in which a changing magnetic field is used to induce an electric current at a specific area of the brain through elec

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Consciousness, at its simplest, is awareness of internal and external existence. However, its nature has led to millennia of analyses, explanations and debates by philosophers, theologians, linguis

Transcranial Magnetic Stimulation of Early Visual Cortex Reveals a Window of Integration of Substantial Duration.

Michael Herzog, Johannes Rüter, Frank Scharnowski

How the brain achieves integration of temporally dispersed information is one of the enigmas in the neurosciences. By combining feature fusion with transcranial magnetic stimulation (TMS), we show that individual visual features are independently stored for several hundred milliseconds before condensed in a conscious percept. We presented two verniers with opposite offset directions in rapid succession at the same retinotopic location. Because of the short durations (30ms each) only one fused vernier is perceived. The perceived offset of the fused vernier is a combination of the offsets of the two verniers which themselves are consciously not accessible. First, we balanced performance at approximately 50%, so that neither the first nor the second vernier dominated the fused percept. We then applied TMS at different times after the onset of the first vernier over the occipital cortex to interfere with visual processing. When TMS was applied from 45ms to 120ms after the onset of the first vernier, the second vernier dominated. For later onset asynchronies of up to 370ms, the first vernier dominated. Hence, even though the individual verniers are not consciously accessible, they still can be manipulated by TMS for a period of more than 300ms. Our results demonstrate that the individual verniers are stored independently for several hundred milliseconds before they are condensed into a conscious percept. Thus, the brain collects and integrates feature information across a broad time window before consciousness. Acknowledgement: This work was supported by the SNSF (Swiss National Science Foundation).

2007

We review here the development of Hodgkin-Huxley (HH) type models of cerebral cortex and thalamic neurons for network simulations. The intrinsic electrophysiological properties of cortical neurons were analyzed from several preparations, and we selected the four most prominent electrophysiological classes of neurons. These four classes are "fast spiking", "regular spiking", "intrinsically bursting" and "low-threshold spike" cells. For each class, we fit "minimal" HH type models to experimental data. The models contain the minimal set of voltage-dependent currents to account for the data. To obtain models as generic as possible, we used data from different preparations in vivo and in vitro, such as rat somatosensory cortex and thalamus, guinea-pig visual and frontal cortex, ferret visual cortex, cat visual cortex and cat association cortex. For two cell classes, we used automatic fitting procedures applied to several cells, which revealed substantial cell-to-cell variability within each class. The selection of such cellular models constitutes a necessary step towards building network simulations of the thalamocortical system with realistic cellular dynamical properties.

2008

Parallel pathways from whisker and visual sensory cortices to distinct frontal regions of mouse neocortex

Alexandros Kyriakatos, Céline Matéo, Carl Petersen, Varun Sreenivasan

The spatial organization of mouse frontal cortex is poorly understood. Here, we used voltage-sensitive dye to image electrical activity in the dorsal cortex of awake head-restrained mice. Whisker-deflection evoked the earliest sensory response in a localized region of primary somatosensory cortex and visual stimulation evoked the earliest responses in a localized region of primary visual cortex. Over the next milliseconds, the initial sensory response spread within the respective primary sensory cortex and into the surrounding higher order sensory cortices. In addition, secondary hotspots in the frontal cortex were evoked by whisker and visual stimulation, with the frontal hotspot for whisker deflection being more anterior and lateral compared to the frontal hotspot evoked by visual stimulation. Investigating axonal projections, we found that the somatosensory whisker cortex and the visual cortex directly innervated frontal cortex, with visual cortex axons innervating a region medial and posterior to the innervation from somatosensory cortex, consistent with the location of sensory responses in frontal cortex. In turn, the axonal outputs of these two frontal cortical areas innervate distinct regions of striatum, superior colliculus, and brainstem. Sensory input, therefore, appears to map onto modality-specific regions of frontal cortex, perhaps participating in distinct sensorimotor transformations, and directing distinct motor outputs. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.

SPIE-Intl Soc Optical Eng2017