Lecture 03. sensory neuro and light.pdf

Lecture 2 1 A bit of history Johannes Müller (1801–1858) nature of a sensation depends on which neurons are active, and not on how the neurons are stimulated. Charles Sherrington (1857–1952) Neurons not physically connected, but work in networks....

Lecture 2 1 A bit of history Johannes Müller (1801–1858) nature of a sensation depends on which neurons are active, and not on how the neurons are stimulated. Charles Sherrington (1857–1952) Neurons not physically connected, but work in networks. 2 A bit of history Wilder PenNeld (1891–1976) Stimulating neurons in certain regions of the brain lead to patients feeling sensation of touches on their body. Horace Barlow (1921 - ) (1972): perception depends on a combination of specialized neurons, each selective for a particular stimulus attribute. 3 The brain has a modular organization The sensory modalities have Some areas of the brain that are , meaning that information from several senses is combined 4 Hermann von Helmholtz (1821–1894)  Invented the ophthalmoscope.  Helmholtz argued that all behaviour could be explained by only physical forces (materialism)  To prove this, he measured the speed of the neural impulse and proved that neurons obey the laws of physics and chemistry 5 Santiago Ramón y Cajal (1852–1934)  Created incredibly detailed drawings of neurons and neural structures  Was the Nrst person to discover the synapse  Won the Nobel Prize in Medicine for his contributions 6 H&E Staining 7 Immuno^uorescence staining 8 generation and transmission of electrical signals in the brain. 9 generation and transmission of electrical signals in the brain. 1 generation and transmission of electrical signals in the brain. 1 generation and transmission of electrical signals in the brain. 1 generation and transmission of electrical signals in the brain. 1 generation and transmission of electrical signals in the brain. Microelectrodes are used to record from single neurons – Recording electrode is inside the nerve Nbre. – Null electrode is outside the Nbre. – Di`erence in charge between them is -70 mV. – This negative charge of the neurone relative to its surroundings is the. Recording Δ=-70mV Null Neuron 1 generation and transmission of electrical signals in the brain. 1 generation and transmission of electrical signals in the brain. 1 generation and transmission of electrical signals in the brain. 1 generation and transmission of electrical signals in the brain. 1 generation and transmission of electrical signals in the brain. 1 generation and transmission of electrical signals in the brain. 2 generation and transmission of electrical signals in the brain. Action potentials remain the same size. Increase in stimulus intensity can of neurons. is 1 ms – upper Nring rate is 500 to 800 impulses/AP’s per second (Hz). of action potentials occurs without stimulation. 2 Electroencephalography (EEG): A technique that, using many electrodes on the scalp, measures electrical activity from populations of many neurons in the brain 2 Event-related potential (ERP): A measure of electrical activity from a subpopulation of neurons in response to particular stimuli that requires averaging many EEG recordings 2 Visually Evoked potentials (VEP): A measure of electrical activity from a sub population of visual neurons in response to a visual stimulus. 2  A technique, similar to EEG, that measures changes in magnetic activity across populations of many neurons in the brain 2  An imaging technology that uses X-rays to create images of slices through volumes of material (e.g., the human body) An imaging technology that uses the responses of atoms to strong magnetic Nelds to form images of structures like the brain 2  functional neuroimaging technique based on measurement of changes in blood ^ow associated with brain activity, using a radioactive substance introduced into the blood. 2  A variant of MRI that makes it possible to measure localized patterns of activity in the brain. Activated neurons provoke increased blood ^ow, which can be quantiNed by measuring changes of oxygenated and deoxygenated blood to strong magnetic Nelds The ratio of oxygenated to deoxygenated hemoglobin that permits the localization of brain neurons that are most involved in a task 2 2 What are the properties of light which humans encode? + 3 Electromagnetic spectrum  Energy is described by wavelength.  Spectrum ranges from short wavelength gamma rays to long wavelength radio waves.  Visible spectrum for humans ranges from 400 to 700 nanometers.  Most perceived light is re^ected light i.e. bounces o` objects within out environment. 3 Physics of Light Light can be absorbed, scattered, re^ected, transmitted, or refracted – Energy (e.g., light) that is taken up, and is not transmitted at all 3 Physics of Light Light can be absorbed, scattered, re^ected, transmitted, or refracted – Energy that is dispersed in an irregular fashion When light enters the atmosphere, much of it is absorbed or scattered and never makes it to the perceiver. 3 Physics of Light Light can be absorbed, scattered, re^ected, transmitted, or refracted – Energy that is redirected when it strikes a surface, usually back to its point of origin 3 Physics of Light Light can be absorbed, scattered, re^ected, transmitted, or refracted – Energy that is passed on through a surface (when it is neither re^ected nor absorbed by the surface) 3 Physics of Light Light can be absorbed, scattered, re^ected, transmitted, or refracted – Energy that is altered as it passes into another medium, (e.g., light entering water from the air) 3  What we have What we want to know about 3