“David Hubel” By Havard Medical School Department of Neurobiology
David H. Hubel was born in Ontario Canada in 1926 and grew up in Montreal. As a child, David’s main interests were in chemistry and electronics which was influenced by his father who was a chemical engineer. Once graduated from Strathcona Academy, Hubel attended McGill college where his favorite classes were physics and mathmathics, but applied to medical school at McGill never taking a biology course. A summer of work at the Montreal Neurological Institute led to an intrest in clinical medicine for neurophysiology which resulted in two years of residency in neurology and a year long internship in neurophysiology. In 1954, Hubel moved to the United States before being drafted into the army as a doctor where he was able to begin his research at the Walter Reed Army Institute of Research. Here he worked with M.G.F. Fuortes on a comparison project of cortical cells in sleeping cats compared to cats that were awake so he decided to focus on a primary sensory and chose the visual system as it was the easiest to work on. Before moving to John Hopkins Hospital to Stephen Kuffler’s laboratory in 1958, Hubel spent a year designing a microelectrode made of tungsten which is tough enough to penetrate the dura. This microelectrode made it possible to record from a single cell from a cat that was looking around which was the start of Hubel’s Nobel prize awarding project (David H. Hubel, 2014).
“David Hubel: The Brain and Visual Perception” From Wellesley College
Hubel worked with Torsten Wiesel through many of their experiments where the receptive fields of single neurons in the retina and visual cortex of cats which had papers published about in 1959 and 1962 respectively. The methods below occured from the experiemnts in the 1962 paper but some information from the 1959 paper is included. Hubel and Wiesel used 40 cats that were prepared by being anaesthetized with thiopental sodium and were paralysed in order to stabalize the eyes with succinylcholine. Contacts were placed on the eyes of the cat to ensure the corneal surface wouldn’t dry out or become cloudy and wire clips were used to keeps the lids in place (Hubel, 1959).
“Hubel and Wiesel Cat Experiment” From Paul Lester
A large screen was placed infront of the cat which had images projected onto it from a tungsten filament projector. Different stimuli could be projected and moved around the screen as well as change size. The size of the projected images were measured in degrees, as 1 mm of retina in the cat is equivilant to about 4 degrees; as a comparison from our view the moon is about half a degree. Ambient background illumination altered in the range of -1.0 to +1.0 log candela per square meter (SI unit of luminous intensity) and the stimuli were between 0.2 and 2.0 log brighter than illumination in the background. Each eye had individual receptive fields measured by marking paper covering the screen. 45 penetrations with the tungsted microelectrode were made to measure responses in individual cells, but never exceeded 4 mm deep and were all made between the lateral and post lateral gyri. Lesions were made during each penetration and measured between 50 and 100 micrometers in diameter which allowed the electrode tip to be identified to the nearest coritcal layer. Track reconstructions were made by calculating the distance from the lesion along the track and also by looking at the subcortical white matter that the electrode passed through (Hubel, 1962).
“Visual Cortex Cell Recording” From Youtube (givn2sin)
The response of the individual neurons would commonly change depending on the size, shape, and movement of the projected light. This broke the 303 cells measured their own respective groups, simple cells, complex cells, and end stopped cells which were formly reffered to as hypercomplex cells. 233 of the cortical cells measured were determined to be simple cells. Simple cells have both excitatory and inhibitory regions which, as we see in Hubel’s experiments, can be mapped. Light introduced to only the exitatory regions causes a response in the cells which increases with more light added to the excitatory region. Light introduced in the inhibitory region does not cause a response until after the light is off in the region. If light is present in the entire cell receptive field, no response is measured when the light is on or off (Hubel, 1962). Simple cells typically have orientation for which a pattern can be seen in the visual cortex (see ice cube model). Lines of light were used in order to measure complex receptive fields which often consisted of unpredictable structures that circular shapes of light could not cause a response to. Complex cells have multiple rigions of exitatory and inhibitory regions throughout the receptive field. Complex cells can also be triggered by a moving line of a specific orientation which can be triggered in both directions or just one. End stopped cells, like complex cells, have multiple regions of inhibitory and exitatory regions but these fields are more specific than complex cells and as a result were left unclassified in Hubel’s 1962 paper. If the line of light is too long, the response is inhibited as there is a specific length of light that can result in the greatest response in the cell field. This data shows that receptive fields of the visual cortex don’t “care” about the brightness of light but respond to specific contours of light and specific orientation and movement of the contour (Wellesley College, 2013). When mapped from their location on the visual cortex, cells in vertical alignment have similar orientation while cells in horizontal alignment rotate slightly. This pattern is seen throughout visual cortex and repeats its self after 1 millimeter. The columns which hold the similar orientation prefrence are known as orientation columns and each of these columns are preferred by one eye or another in columns known as ocular dominance columns, shown as L and R in the ice cube model.
“Ice Cube Model” From David Hubel’s Eye, Brain, and Vision
The work done by David Hubel opens our eyes to one of the most important structures of the brain which we now have more information on than almost any other part of the brian. This work was clearly deserving of the nobel prize award which was awarded to Hubel in the field of physiology and medicine in 1981 between him and Torsten Wiesel “for their discoveries concerning information processing in the visual system” (The Nobel Prize, 2014). After his research at John Hopkins Hosptial, he joined Harvard’s neurobiology staff in 1982 and where he retired from in January of 2013. David Hubel passed away in September of 2013 (Gryzbowski, 2014), but his work in the field of neurobiology will inspire many in generations to come. Here is a link to David Hubel’s nobel lecture
Hubel, D. H., & Wiesel, T. N. (1962). RECEPTIVE FIELDS, BINOCULAR INTERACTION AND FUNCTIONAL ARCHITECTURE IN THE CAT’S VISUAL CORTEX. Physiol, 106-154. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1359523/pdf/jphysiol01247-0121.pdf.
Hubel, D. H., & Wiesel, T. N. (1959). RECEPTIVE FIELDS OF SINGLE NEURONES IN THE CAT’S STRIATE CORTEX. Physiol, 574-591. Retrieved from http://onlinelibrary.wiley.com/store/10.1113/jphysiol.1959.sp006308/asset/tjp19591483574.pdf?v=1&t=jerhw5c1&s=66cbcebf617157306472be8b61e610e1e154b288
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