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Electromagnetic Neuroimaging Methods 16 January 2024 15:57 Main Ideas Notes All regions of brain active within 100 ms Latencies of visually-responsive neurons in monkey brain Notes Notes MEG recording setup Analyses in frequency domain ○ Decompose signals into constituent brain rhythms ○ Brain rhyth...

Electromagnetic Neuroimaging Methods 16 January 2024 15:57 Main Ideas Notes All regions of brain active within 100 ms Latencies of visually-responsive neurons in monkey brain Notes Notes MEG recording setup Analyses in frequency domain ○ Decompose signals into constituent brain rhythms ○ Brain rhythm examples ▪ State related ○ High-level visual discrimination also take place early (Rainer et al., 1999 - looked at cell firing rates in monkey prefrontal cortex) Electromagnetic brain activity To know when things happen, electroencephalography (EEG) or magnetoencephalography (MEG) most often used. Mental processes cause changes in neuronal activity EEG recording set-up ▪ Event related □ What is EEG/MEG Some neuronal populations generate an electromagnetic field from inner to outer surface. ○ Electrical component: EEG. ○ Magnetic component: MEG. Analysing EEG recordings Event-related potentials: ○ Small changes induced by events Detectable inside and outside of the head (mostly done outside) Source localisation Scalp fields do not directly reflect which part(s) of the brain give rise to the signals. ○ Source(s) not necessarily underneath maximal activity Inverse problem. ○ Cannot uniquely estimate intracerebral sources due to smearing/distortion during volume conduction and limited number of electrodes (better with MEG) Scalp-recorded activity Volume conduction: some electromagnetic fields propagate through tissue and can be measured on the scalp Detectable inside and outside of the head ○ ○ Requirements ○ electromagnetic field must be large in order to be detectable and measurable ○ requires summated activity of thousands of neurons - cannot look at a few neurons ○ The neurons must be active synchronously. ▪ Action potentials (~1 ms) unlikely. ▪ Graded post-synaptic potentials most likely ○ neurons must have an open field spatial configuration - neuron able to travel to the surface EEG vs. MEG EEG picks up more brain activity than MEG. ○ EEG: sources can be deep or shallow and radial or tangential. ○ MEG: sources must be shallow and tangential. MEG easier to obtain and localise, but expensive Summary PSYC0031 Cognitive Neuroscience Page 1 Source estimation Intracerebral sources can sometimes mathematically be estimated. ○ Need to rely on other knowledge and make assumptions. Sentence in mind: I drink my coffee with milk and --- N stand for negative Maximal activity occurs at 400 Additiona Whe ▪ ▪ ▪ ▪ Notes Notes l considerations en choosing a technique to answer a question of interest, also consider: ▪ - the cost, availability and comfort of a technique. ▪ - compatibility with equipment. ▪ - suitability for experimental design. ▪ - how to connect different parts of the experiment. PSYC0031 Cognitive Neuroscience Page 2 Notes PSYC0031 Cognitive Neuroscience Page 3 Notes Notes PSYC0031 Cognitive Neuroscience Page 4 PSYC0031 Cognitive Neuroscience Page 5