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Outline for cognitive neuroscience Chapter 1 Introduction to Method Outline and page number Experimental methods in cognitive neuroscience 1. Animal experiment (P106-112): single cell recording, lesion, *genetic manipulation 2. *neurology 3. Converging methods A. cognitive deficits following brain damage(P124-126): single vs double dissociation B. TMS (P128) C. Functional imaging: ERP(P129-134), MEG(P135), PET and fMRI(P136-143) Gist Single-cell recording This method enable researchers to describe response characteristics of individual elements(precise and causal). Single-cell recording is done extracellularly in order not to damage the neuron measured. Background noise vs action potential: neurons in different areas and circumstance have different background firing rate, that is the neuronal firing rate when no stimulus is presented. This renders the exact firing rate of neurons meaningless, what counts is the change of firing rate in different conditions. Single-cell recording is essentially a correlational approach. Stimuli-firing rate -> response characteristics; Receptive field of neuron: the function of neuron firing rate that depends on the spatial-temporal variables of stimuli. In visual system, the RF is smallest in the primary visual cortext and become larger toward higher visual cortex. Topographic representation: orderly relation between the RF properties of neurons and the external world. Limitation: being a correlational approach, it is hard to establish casual relationship. Lesions Basic method: remove one or more parts of the brain and measure the change of behavior. Underlying logic: if a neural structure contributes to a task, then rendering the structure dysfunctional should impair the performance. Problems with lesion study: Lesion may force the animal to alter the operation of intact structure Lesion may cause the animal to develop a compensatory strategy to minimize the consequences of the lesion. Newer method: Neurochemical lesions Cooling Cognitive deficits following brain damage Why we study patient with brain lesion? The complex cognitive task require the integrative activity of many component operations. Patient with specific brain lesion may lost the ability of one particular operation. Study dysfunctional behavior can help identify the component operations that underlie normal cognitive performance. Keep in mind: the challenge for the cognitive neuroscience is to determine whether the observed behavioral problem results from damage to a particular mental operation or is secondary to a more general disturbance. Single vs double dissociations Single dissociation: two groups (patients with a particular lesion & control), two task(one highly depend on the interested cognitive operation while the other relatively irrelevant to that operation). The performance of experimental group is significantly worse than the control group. But the difference may result from more general factors such as the relative difficulty of the two tasks. Double dissociation: two (or more) groups(patients with a particular lesion & patients with another type of lesion), two task (one highly depend on the interested cognitive operation while the other on another operation). The performance of Group A is worse than that of Group B in task A, whereas the performance of Group B is worse than that of Group A in another task. Strong evidence that a group of patient has a selective deficit in a certain operation. TMS Temporarily disrupt the function of a selective brain region(1-1.5 cm2)-> degeneration of a certain behavioral performance: causal relationship between the function of that region and that performance. Also can investigate the time-course of a cognitive process: disrupt certain brain area at different intervals after on-set of that process. Limitation of TMS: only able to study the simple and straightforward processes. Only able to study the function of cortical areas that are superficial surface of the brain. ERP(EEG) Principle: a particular cognitive process will induce a convergent brain activity and thus a convergent scale potential pattern. This convergent pattern is superposed onto the background activity, which is random over time. thus when averaging the EEG waveform caused by many same process will render the noise vanishing and the waveform that reflects the specific cognitive process salient. Advantage of ERP: Since the brain potential follows neuronal activity immediately, ERP provides a precise temporal record of underlying neural activity. Problem with ERP: poor spatial resolution: neural generator is difficult to localized from the potential distribution on the scalp. ERF(MEG) Principle: active neurons also produce small magnetic fields that propagates to the scale without distortion. Record the time course and distribution of magnetic fields time-locked to specific event-> event-related field. Advantage of ERF: similar temporal resolution with ERP but higher spatial resolution. Problems with MEG It is only possible to detect current flow that is oriented parallel to the surface of the skull; Too expensive. PET and fMRI Fundamental principle: measure the changes in metabolism or blood flow in the brain while the subject is engaged in cognitive tasks. Therefore, these methods are correlational. PET Underlying assumption: there will be increased blood flow to the brain regions that engaged in cognitive processes. Measured index: regional cerebral blood flow(rCBF) Inject tracer to the blood. detect the gamma ray emitted by the isotope in the blood. Spatial resolution: 5-10 mm3 ; temporal resolution: tens of second. fMRI underlying assumption: the active neurons require more oxygen to fulfill their energy consumption-> increased blood flow carry much more oxygenated hemoglobin than the neurons can consume immediately-> increase of the ratio of oxygenated to deoxygenated hemoglobin-> oxygenated and deoxygenated hemoglobin have different magnetic properties that can be detect by the scanner. Measured index: blood oxygenation level dependent effect, BOLD. The reason for the prevalence of fMRI(comparison with PET): MRI scanner is more available than PET Methodological advantage: Relatively high spatial and temporal resolution of fMRI Same subject can be measured repeatedly->statistical analysis of single subject BOLD can be time-lock to specific event, allowing more flexible experimental design. Problem with PET and fMRI Correlational approach: correlation does not imply causation. Poor temporal resolution in comparison with ERP