Cognitive Neuroscience PDF

Topic 2 Cognitive Neuroscience  What is cognitive neuroscience? Neuroscience is the scientific study of the nervous system.  What is cognitive neuroscience? Cognitive neuroscience is the scientific study of the relation between the nervous system and cognition....

Topic 2 Cognitive Neuroscience  What is cognitive neuroscience? Neuroscience is the scientific study of the nervous system.  What is cognitive neuroscience? Cognitive neuroscience is the scientific study of the relation between the nervous system and cognition. ?  Building Blocks of the Nervous System Neurons: cells specialized to receive and transmit information in the nervous system The brain is composed of ~100 billion neurons (cells) and > 100 trillion synapses (connections); Each neuron has a cell body, an axon, and dendrites. Caption: Basic components of the neuron. The bottom neuron contains a receptor, which is specialized to receive information from the environment (in this case, pressure that would occur from being touched on the skin). This neuron synapses on the top neuron, which has a cell body instead of a receptor.  Building Blocks of the Nervous System Cell body: contains mechanisms to keep cell alive Axon: tube filled with fluid that transmits electrical signal (towards other neurons) Dendrites: multiple branches reaching from the cell body, which receive information from other neurons. Caption: A portion of the brain that has been treated with Golgi stains shows the shapes of a few neurons. The arrow points to a neuron’s cell body. The thin lines are dendrites or axons.  How Neurons Communicate Action potential (spike) – Neurons receive signal from environment  How Neurons Communicate Caption: (a) Action potentials are recorded from neurons with tiny microelectrodes that are positioned inside or right next to the neuron’s axon. These potentials are displayed on the screen of an oscilloscope and are also sent to a computer for analysis. (b) An action potential recorded by a microelectrode looks like this. The inside of the axon becomes more positive, then goes back to the original level, all within 1 millisecond (1/1,000 second). (c) A number of action potentials displayed on an expanded time scale, so a single action potential appears as a “spike”.  How Neurons Communicate Caption: Records showing action potentials in a neuron that responds to light entering the eye. (a) Presenting light causes an increase in firing; (b) increasing the light intensity increases the rate of firing further; and (c) even more light results in a high rate of firing.  How Neurons Communicate – Information travels down the axon of that neuron to the dendrites of another neuron  How Neurons Communicate Measuring action potentials – The size is not measured; size remains (mostly) constant – The rate of firing is measured. In general: Low intensity input: slow firing High intensity input: fast firing  How Neurons Communicate Synapse: space between the axon of one neuron and a dendrite from another neuron When the action potential reaches the end of the axon, synaptic vesicles open and release chemical neurotransmitters Neurotransmitters cross the synaptic space and bind with the receiving dendrite How neurons communicate  How Neurons Communicate Neurotransmitters: chemicals that affect the electrical signal of the post-synaptic neuron – Excitatory: increases the likelihood that the post- synaptic neuron will produce a spike (e.g., glutamate) – Inhibitory: decreases the likelihood that the post- synaptic neuron will produce a spike (e.g., GABA) – Or both, depending on context (e.g., dopamine)  How Neurons Process Information Not all signals received lead to action potential The cell membrane processes the number and timing of impulses received An action potential results only if the threshold level is reached – Interaction of excitation and inhibition Questions? Representation in the brain  Representation in the Brain Feature detectors: neurons that respond best to a specific stimulus Hubel & Wiesel (1965) – Simple cells: neurons that respond best to bars of light of a particular orientation – Complex cells: neurons that respond best to an oriented bar of light with a specific length  Representation in the Brain Specificity coding: representation of a specific stimulus by firing of specifically tuned neurons specialized to just respond to a specific stimulus Distributed coding: representation by a pattern of firing across a large number of neurons Distributed Coding  Representation in the Brain Specificity coding: representation of a specific stimulus by firing of specifically tuned neurons specialized to just respond to a specific stimulus Distributed coding: representation by a pattern of firing across a large number of neurons Sparse coding: Distributed representations using a small number of neurons (likely solution) Questions?  Localization of Function Specific functions are served by specific areas of the brain Cognitive functioning breaks down in specific ways when areas of the brain are damaged Cerebral cortex (in humans, a 3-mm thick layer that covers the brain) contains mechanisms responsible for many cognitive functions Subcortical areas, such as the basal ganglia, also have important cognitive function Lobes of the Cerebral Cortex Subcortical structures  Method: Lesions Schnyer et al. (2009). Neuropsychologia. A or B?  Method: lesions Ventral PFC lesion affects performance in perceptual categorization! Schnyer et al. (2009). Neuropsychologia.  Method: lesion Lesions are one of the oldest methods used to localize functions; With non-human animals, we can experimentally lesion animals; However, lesions in humans need to be accidental, and are rarely focal; One solution is transcranial magnetic stimulation (TMS); Method: TMS  Method: TMS TMS can be used to: – Safely reproduce the effect of a temporary cortical lesion; – Temporarily add noise to neural activation (rTMS).  Method: TMS Sequence production  Method: TMS Verwey et al. (2002). Neuropsychologia.  Method: Inactivation TMS works well but it is restricted to cortical regions; With non-human animals, we use inactivation methods; For example, muscimol is a GABA agonist; So, we can use muscimol to selectively inactivate brain structures with GABA receptors – e.g., the basal ganglia; Method: Inactivation X X  Method: Inactivation The basal ganglia is not involved in automatic sequence production! Desmurget & Turner (2008). Journal of Neuroscience. Questions??  Method: Brain Imaging Positron Emission Tomography (PET) – Blood flow increases in areas of the brain recruited by a cognitive task – A radioactive tracer is injected into participant’s bloodstream – Measures signal from tracer at each location of the brain – Higher signals indicate higher levels of brain activity Caption: (a) Person in a brain scanner. (b) In this cross section of the brain, areas of the brain that are activated are indicated by the colors. Increases in activation are indicated by red and yellow, decreases by blue and green  Method: Brain Imaging Subtraction technique measures brain activity before and during stimulation presentation Difference between activation determines what areas of the brain are active during the manipulation (remember Donders?) Caption: The subtraction technique used to interpret the results of brain imaging experiments.  Method: Brain Imaging Functional Magnetic Resonance Imaging (fMRI) – Subtraction technique – Measures blood flow through magnetic properties of blood – Advantage: no radioactive tracer needed Method: Brain imaging A or B?  Method: Brain imaging Hélie et al. (2010). Journal of Neuroscience. Method: Brain imaging  Method: Electroencephalography (EEG) Neuron “firing” is an electrical event EEG measures electrical activity on the scalp to make inferences about underlying brain activity When time-locked and averaged over a large number of trials, EEG is used to calculate event-related potentials (ERPs) Caption: (a) Person wearing electrodes for recording the event- related potential (ERP). (b) An ERP to the phrase “The cats won’t eat.”  Method: Electroencephalography (EEG) Neuron “firing” is an electrical event EEG measures electrical activity on the scalp to make inferences about underlying brain activity When time-locked and averaged over a large number of trials, EEG is used to calculate event-related potentials (ERPs) Advantage: continuous and rapid measurements Disadvantage: does not give precise location  Localization of Function Lesions, TMS, and inactivation are reliable but require a strong theory about the location of the function; PET and fMRI allow for more exploration, and the spatial resolution of fMRI is much higher (~ 1-3 mm); However, the temporal resolution is low (typically > 1 sec); EEG has better temporal resolution (in ms) but poor spatial resolution. Questions? Lobes of the Cerebral Cortex  Lobes of the Cerebral Cortex Frontal – Reasoning and planning – Language, thought, memory, motor functioning Parietal – Visual attention – Touch, temperature, pain, and pressure Temporal – Auditory and perceptual processing – Language, hearing, memory, perceiving forms Occipital – Visual processing  Localization of Function: Subcortical areas Basal ganglia: Categorization, sequence processing Hippocampus: forming memories Amygdala: emotions and emotional memories Thalamus: relaying information from vision, hearing, and touch senses  Distributed Processing in the Brain However, specific cognitive functions are often processed by many different areas of the brain Many different areas may contribute to a function Questions?  Do brains make us lose our minds? Weisberg, Keil, Goodstein, Rawson & Gray (2008): The seductive allure of neuroscience explanations Are explanations of psychological phenomena more satisfying when they contain neuroscientific facts? Method – 18 descriptions of psychological phenomena – Independent variables: Soundness of explanation: good vs. bad Inclusion of neuroscientific explanation: yes vs. no – Dependent variable: Participants rate how satisfying the explanation is (7- point scale) -3 very unsatisfying to +3 very satisfying Phenomenon: Difficulty with inferring what other people know…  Exp. 1 – Non-Expert undergraduates Neuroscientific facts do not change evaluation of good explanations But they make bad explanations more acceptable!  Exp. 2 - Cognitive neuroscience students Neuroscientific facts make everything sound better! Beginning/after class: No difference  Exp. 3 – Neuroscience Experts Useless: Makes good explanation look worse A bad explanation is a bad explanation…  What about pictures of brains? McCabe and Castel (2008): Seeing is believing: The effect of brain images on judgments of scientific reasoning Does the inclusion of neuroscientific images of the brain influences people’s evaluation of scientific documents? 66  Method Participants read fictional articles on scientific topics (e.g., Watching TV is related to math ability) that are open to criticism Articles include text only, text + bar graph or a text + brain images Participants must determine if the scientific reasoning in the article makes sense (0-4) 67  Results Simple visual representation has no effect Images of brain make scientific reasoning look more adequate  Conclusions about both experiments Weisberg et al. (2008) and McCabe and Castel (2008) both suggest that explanations of psychological phenomena appear better if they are accompanied by neuroscience (at least to non-experts) We need to be careful in interpreting cognitive neuroscience data Expert (neuro)scientists must take back control of the public scientific discourse 69 Questions??  Week summary (1) Cognitive neuroscience is the scientific study of the relation between the nervous system and cognition; A neuron is composed of a body, axon, and dendrites; The membrane potential of a neuron can be recorded using microelectrode; Neurons communicate together using neurotransmitters;  Week summary (2) Neural coding is likely to be sparse; Brain functions can be localized using various methods, e.g., lesions, inactivation, TMS, and neuroimaging; Bad explanations of psychological phenomena appear better if they are accompanied by neuroscience data; We need to be careful in interpreting cognitive neuroscience data.  Example question One theory is that individual stimuli (such as faces, for example) are represented in the brain by multiple neurons firing in a specific pattern. This idea is called: a) the grandmother cell hypothesis b) distributed coding c) specificity coding d) semantic coding