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Chapter 1: Neuron/MethodsNeuron- Huxley and Hodgkinso Worked out details of electrical properties of axonso Shared Nobel prize in 1963 with Eccles- Creating potentials in neuronso Neural membranes separate ionic charges Charges differ inside-to-outside (called the resting potential)o Separation is a high energy state Certain conditions cause a rapid reversal of that state The signal produced is called the action potential (AP)- The lipid bi-layero Impermeable to many moleculeso Do any materials pass through? Placed throughout the lipid bi-layer are ionic channels- Allow for the passage of certain ions, but not otherso What is allowed through? Allows for the passage of some ions- Potassium (K+)o Potassium movement K+ moves somewhat freely across the cell membrane Due to the inside of the cell being negative, K+ moves into the cell but then exits (diffusion) An equilibrium is eventually reached (corresponds to the resting potential -70 mV) But not others- Proteins- Sodium (Na2+)- Action Potentialo Moment of libertyo Sodium channels in the membrane briefly become permeable Causes of massive current (ion) flowo Resting potential vanishes and is even slightly reversedo Hyperpolarization- inside of the neuron becomes more negative o Steps Resting potential is established Action potential is created when voltage dependent (or –gated) ion channels are triggered- Triggers- when the membrane becomes slightly depolarized sodium (+) channels open, allowing a rapid influx of these ions which momentarily reverses the resting potential- Postsynaptic ion channels o Transmitter-gatedo Channels stay open for as long as the transmitter molecules are presento The more transmitter present in synapses, the more ion channels opened Thus the signal received at postsynaptic membranes is graded (in contrast to all-or-none APs)o The postsynaptic membrane passively conducts potentials Does not produce APso Excitatory postsynaptic potentials (EPSPs)o Inhibitory postsynaptic potentials (IPSPs)- Summation of potentialso Postsynaptic potentials decay relatively slowlyo Multiple synaptic inputs are summed (spatial summation) Special summation depends on multiple inputs action (more or less) simultaneouslyo Rapid presynaptic inputs are also summed (temporal summation) Temporal summation depends on rapid release of neurotransmitter by fewer inputso EPSPs and IPSPs cancelo If sufficient depolarization reaches the cell’s axon, an AP is generated (at the axonhillock)Electroencephalography (EEG)- Hans Berger (1929)o Placed electrode on scalp and plotted electrical activityo Results were controversial at the timeo However, EEG was eventually accepted into the scientific community- EEGo Electrodes are placed on the scalp to measure electrical activityo Postsynaptic potentials- Event-related potential (ERP)o Electrical brain activity measured from the scalp and evoked by a stimulus event- Pros/Cons of EEGo Advantages- great temporal resolution, relatively inexpensiveo Disadvantages- poor spatial resolution, participants must go through many trialsTranscranial Magnetic Stimulation (TMS)- A technique whereby a brief intense pulse of magnetic energy is applied to the scalp to temporarily disrupt normal processingFunctional Magnetic Resonance Imaging (fMRI)- Neuroimaging technique that capitalizes on the fact that neural activity triggers a temporary increase in metabolic demand at the site of activationo Oxygenated blood has different properties than deoxygenated blood- Pros/Conso Advantages- great spatial resolutiono Disadvantages- poor temporal resolution, loud, expensivePositron Emission Tomography (PET)- Imaging technique capitalizing on the brain’s need for glucose and oxygeno A (safe) radioactive substance is injected that “tags” glucose or oxygen atoms- Pros/Conso Advantages- quito Disadvantages- radioactive substance, poor spatial resolution (relative to fMRI)Methods for Understanding PerceptionThresholds- Ernst Weber (1795-1878)o Weber found that the just noticeable difference (JND- smallest detectable difference between two stimuli) depends upon the referent- Gustav Fechner (1801-1887)o Developed psychophysics- specifying quantitative relations between physical stimuli and how they are perceivedo Used Weber’s findings to establish Weber’s law Change in I = K Io Extended law to create Fechner’s law: S= k log R Assumes that all JND’s are the same- Thresholdso Absolute threshold- the minimum amount of stimulus that a person can detecto Difference threshold- same as the JNDo Different methods for measuring thresholds Method of constant stimuli- Psychophysical procedure in which each of a fixed set of stimuli is presented in a random order- After completing all possible comparisons, a JND can be computedthat is noticeably stronger and noticeably weaker Method of Limits- Similar to the method of constant stimuli- Comparison stimuli start at a level of intensity either higher or lower than the standard and decrease or increase (for descending and ascending respectively)- Ascending series- start with a stimulus that is initially weaker than the standard- Descending series- start with a stimulus that is initially stronger than the standard- Pro- efficient- Con- expectations Staircase procedure- Variant of the method of limits- Stimulus presentations, governed by the person’s responses, are made to bracket the threshold- Alternating between 2 different staircases can reduce expectationsScaling- Scaling Methodso Ratings in gymnastics and ice skating are examples of scaling methodso Magnitude Estimation A psychophysical procedure in which people assign numbers to stimuli in proportion to the perceived intensity of those stimuli S = aI^bSignal Detection Theory (SDT)- Method used to quantify the ability to detect signal from noise- Assumes an active part on the perceiver- decision must be made- Criterion= internal threshold set by the observer- Possible states of the world in SDTo Signal/response= yes- HITo Signal= no/response=yes- FALSE ALARMo Signal=yes/response=no-MISSo Signal/response=no- CORRECT REJECTIONo Based on this info, we can calculate a measure of sensitivity- quantify how well signal is detected from noise- Receiver Operating Characteristic (ROC) curveso ROC curve- a plot of the hits and false alarms- SDT applied to memory paradigms- used to examine recognition memoryTheoretical Approaches- Computation/Ideal

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UMD PSYC 310 - Chapter 1: Neuron/Methods

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