Category: Nezařazené

A neural mechanism for exacerbation of headache by light

2010 study

Rodrigo Noseda, Vanessa Kainz, Moshe Jakubowski, Joshua J. Gooley, Clifford B. Saper, Kathleen Digre, Rami Burstein

The perception of migraine headache, which is mediated by nociceptive signals transmitted from the cranial dura mater to the brain, is uniquely exacerbated by exposure to light. Here we show that exacerbation of migraine headache by light is prevalent among blind persons who maintain non-image-forming photoregulation in the face of massive rod/cone degeneration. Using single-unit recording and neural tract-tracing in the rat, we identified dura-sensitive neurons in the posterior thalamus, whose activity was distinctly modulated by light, and whose axons projected extensively across layers I through V of somatosensory, visual and associative cortices. The cell bodies and dendrites of such dura/light-sensitive neurons were apposed by axons originating from retinal ganglion cells, predominantly from intrinsically-photosensitive retinal ganglion cells – the principle conduit of non-image-forming photoregulation. We propose that photoregulation of migraine headache is exerted by a non-image-forming retinal pathway that modulates the activity of dura-sensitive thalamocortical neurons.

Migraine is a recurring, episodic neurological disorder characterized as a unilateral, throbbing headache that is commonly associated with a variety of other symptoms (e.g., nausea, vomiting, irritability, fatigue). Migraine pain is thought to originate from chemical irritation of the meninges, which leads to transmission of nociceptive signals from the dura mater to the brain via the so-called trigeminovascular pathway. The first- and second-order neurons in this pathway are, respectively, sensory neurons in the trigeminal ganglion that project centrally to the spinal trigeminal nucleus (SpV), and dura-sensitive neurons in laminae I and V of SpV that project to the posterior thalamus. Prolonged neuronal activation during a migraine attack is thought to induce peripheral and central sensitization along the trigeminovascular pathway, which explains the throbbing of headache and the accompanying scalp and neck-muscle tenderness, and whole-body cutaneous allodynia.

More about this study can be found at this link

Caveman: An Interview with Michel Siffre

Article from 2008

Michel Siffre - scientist based in Paris, author of several books, including Beyond Time (McGraw-Hill, 1964) and Découvertes dans les grottes mayas (Arthaud, 1993).

Joshua Foer - freelance science writer.

In 1962, a French speleologist named Michel Siffre spent two months living in total isolation in a
subterranean cave, without access to clock, calendar, or sun. Sleeping and eating only when his body told
him to, his goal was to discover how the natural rhythms of human life would be affected by living
“beyond time.” Over the next decade, Siffre organized over a dozen other underground time isolation
experiments, before he himself returned to a cave in Texas in 1972 for a six-month spell. His work helped
found the field of human chronobiology. Joshua Foer interviewed Siffre by email.

Whole interview here.

Opponent melanopsin and S-cone signals in the human pupillary light response

2014 study

Manuel Spitschana , Sandeep Jainb , David H. Brainarda,1, and Geoffrey K. Aguirreb,1

Departments of a Psychology and b Neurology, University of Pennsylvania, Philadelphia, PA 19104

Edited by Dennis M. Dacey, The University of Washington, Seattle, WA, and accepted by the Editorial Board September 12, 2014 (received for review January 17, 2014)

In the human, cone photoreceptors (L, M, and S) and the melanopsincontaining, intrinsically photosensitive retinal ganglion cells (ipRGCs) are active at daytime light intensities. Signals from cones are combined both additively and in opposition to create the perception of overall light and color. Similar mechanisms seem to be at work in the control of the pupil’s response to light. Uncharacterized however, is the relative contribution of melanopsin and S cones, with their overlapping, short-wavelength spectral sensitivities. We measured the response of the human pupil to the separate stimulation of the cones and melanopsin at a range of temporal frequencies under photopic conditions. The S-cone and melanopsin photoreceptor channels were found to be low-pass, in contrast to a band-pass response of the pupil to L- and M-cone signals. An examination of the phase relationships of the evoked responses revealed that melanopsin signals add with signals from L and M cones but are opposed by signals from S cones in control of the pupil. The opposition of the S cones is revealed in a seemingly paradoxical dilation of the pupil to greater S-cone photon capture. This surprising result is explained by the neurophysiological properties of ipRGCs found in animal studies.

Whole study on this link