Neurodynamic Neuroimaging Methods PDF

Neurodynamic Neuroimaging Methods 11 January 2024 15:54 Main Ideas Notes What is neuroimaging? The use of techniques that portray the structure and function of the human brain Includes a range of techniques Subset of all cognitive neuroscience methods. ○ Others include brain stimulation, brain lesio...

Neurodynamic Neuroimaging Methods 11 January 2024 15:54 Main Ideas Notes What is neuroimaging? The use of techniques that portray the structure and function of the human brain Includes a range of techniques Subset of all cognitive neuroscience methods. ○ Others include brain stimulation, brain lesions, eye tracking, neural network modelling, physiological responses, behaviour Classification of techniques Structure vs. function Temporal vs. spatial resolution Degree of invasiveness Correlation vs. causation Structural imaging Detailed, static anatomical brain pictures Interest in morphology: size, shape, density, integrity of grey and white matter structures Techniques based on distinct tissue properties X-rays, computerised tomography (CT), structural MRI MRI Localise tissue within the head by manipulating and measuring behaviour of protons Put person’s head in a strong magnetic field. Transmit brief radio wave (electromagnetic radiation). Turn off radio wave. Receive signal back from person. Convert signal into image Notes 4. Time measures T1 (spin-lattice relaxation): time for protons to re-align to the static magnetic field (B0). T2 (spin-spin relaxation): time for protons to de-phase due to interactions between spins (T2 < T1). T2*: rapid loss in coherence of protons and faster de-phasing because of local magnetic field inhomogeneities (T2* < T2). Resulting images ▪ Safety issues MRI is safe with precautions and training. Strong magnetic fields, helium, and phantom liquids can result in serious injury/damage Magnetic field is always on: No ferromagnetic objects. Metal safety checks. MRI-compatible equipment Other issues: noisy and confined space, heating up of tissue, peripheral stimulation, cold environment Structural MRI approaches Differences in anatomy (volume/density). 3. After radio wave, the energy associated with re-aligning to the original B0 field is used to create an image. ○ Time measures (ms): T1 / T2 / T2* Summary PSYC0031 Cognitive Neuroscience Page 1 fMRI ○ Oxygenated and de-oxygenated hemoglobin emit different energies as they relax back to B0 magnetic field. ○ More neural activity --> more oxygenated blood --> increase in signal. Based on capturing physiological changes associated with cognitive processing. Hemodynamic techniques One class of functional imaging relies on the brain’s blood supply. The idea is that: - The brain is metabolically demanding. - When a region is active, more oxygen and glucose are needed. - This leads to more, and more oxygenated, blood to that region. - More is supplied than is needed. - Measuring blood flow and/or oxygenation indicates which regions are active. Same scanner Scannin Differen fNIRS Only rea Key adv Relative EXAMP ○ N ○ A ○ fN ○ ○ Spatial resolution ~1 mm; some regions difficult to image; movement and equipment can be a problem. Diffusion/perfusion imaging: white matter tracts and pathologies. Functional imaging Interest is in brain function. Detailed, varying functional brain pictures. fM Optical neuro Also bas Infrared Biologic Functio Localisation Different tissues can be identified because they emit different energies. Gradients in the magnetic field used to localise where the signals come from. Many factors contribute to MRI (e.g., nuclear spin properties, tissue relaxation, echo times). 1. MRI uses magnetic fields to distort behaviour of protons ○ Tissue contains water molecules, which contain hydrogen atoms which contain protons 2. Protons precess or 'wobble' ○ Application of a brief, specific radio wave causes re-orientation of protons (“excitation”). Notes Positron emission tomography (PET) ○ Measures blood flow. ○ Radioactive tracers injected into blood stream. ○ Breakdown of tracer leads to release of 2 gamma rays in opposite directions, detected by PET scanner. ○ Spatial resolution ~10mm; ○ whole brain can be measured. ○ Now, mostly used for clinical purposes fMRI signal ▪ Referred to as Blood Oxygen Level Dependent (BOLD) response. ▪ Deoxyhemoglobin distorts magnetic fields, causing spins to lose coherence faster (smaller T2*). ▪ More neural activity leads to, proportionally, less deoxyhemoglobin (larger T2*) fMRI Acquisition ▪ Brain images acquired in parts, □ Each 3-dimensional image referred to as a volume □ Each volume acquired via slices, consisting of voxels ▪ Analyses consider activity in all voxels. ▪ With >100,000 voxels in typical image, large amount of data to analyse Time courses Neuroim Howeve Not suff Notes MRI analyses ▪ Foci of activations: which brain region(s) differ in activity? ▪ Multi-voxel analyses: are there identifiable activity patterns within a region? ▪ Connectivity: how do regions interact? r, different heads ng sequences used to tailor signals. nt types of participants can be scanned. oimaging sed on the brain’s blood supply. d light shone onto scalp. cal tissue fairly transparent; light reaches brain tissue and is absorbed and scattered. nal Near-Infrared Spectroscopy (fNIRS) measures changes in oxy- and deoxyhemoglobin (different colours). aches superficial tissue (~3 cm), but cheaper than fMRI, quiet, tolerates movement artifacts, and suitable for everyone. vantage: portability. ely new; equipment and analyses being developed. LE eurodevelopment of auditory processing in low -resource setting. t what age do Gambian infants separate social and non-social sounds (e.g., yawns vs. rattle)? NIRS signals in anterior temporal cortex sensitive to social sounds from 9 months onwards (similar to UK infants). ▪ maging methods based on the brain's blood supply have excellent spatial resolution er, they have limited temporal resolution because blood parameters only change slowly ficiently precise to measure fast changes in the brain and mind PSYC0031 Cognitive Neuroscience Page 2 Notes Notes PSYC0031 Cognitive Neuroscience Page 3 Notes Notes PSYC0031 Cognitive Neuroscience Page 4 PSYC0031 Cognitive Neuroscience Page 5