- Implemengtation requires surgical procedure which is expensive & risky because of transplant medical complication such as transplant rejection.
- Implanted electrode are fixed and can oly record brain signals from the same location.
Involves the insertion of electrodes into the cortex of the subject's brain. Action Potential: "Spike",all-or-none output of single neurons Field Potential: summed voltage fluctuations from small to large number of neurons.
high SNR,high spatial resolution,low surgical risk,BW 0-500Hz ECoG is an extracortical invasive electrophysiological monitoring method to record brain activity. ECoG provides a tradeoff between higher SNR compared to noninvasive recordings and lower risk compared to intracortical recordings.
-signal collected using electricval,magnetic or metabolic methods. -fNIRS,fMRI,EOG,MEG
-Monitors the voltage fluctuations generated by an electrical current within human neurons. -Electrodes placed on the scalp measure the amplitude of EEG signals. -Low spatial resolution: since the number of electrodes are limited. -EEG electrode locations generally folow the international 10-2- system or the intermediate 10% electrode positions. -International 10-2- system divides the scalp in 10% and 20% intervals and totally contains 21 electrode locations.
*Tempooral resolution>Spatial resolution.The ionic current changes rapidly,which offers a temporal resolution higher than 100Hz.
SNR of EEG is poor: Objective Factors - environmental noises,the obstruction of the skull and other tissues between cortex and scalp,various simnulations Subjective Factors- contains the mental stage of the subject,fatigue status, and the variance among different subjects.
Delta pattern(0.5-4Hz): Deep sleep Theta pattern (4-8Hz) : light sleep Alpha pattern(8-12Hz) : eyes close deeply relaxed Beta pattern(12-30Hz) : eyes open & high awareness,daily activities(eating,walking,talking) Gamma pattern(30-100Hz) :
-fNIRS employs NIR light to measure the aggregate degree of oxygenated hemoglobin(Hb) and deoxygenated-hemoglobin(deoxy-Hb) because Hb and deoxy-Hb have higher abosrbance of light than other components such as the skull or hemodynamic response to form a functional neuroimage. -fNIRS relies on blood-oxugen-level-dependent(BOLD) response or hemodynamic response to form a functional neuroimage. -fNIRS can't measure cortical activity occuring deeper than 4 cmin the brain
-Monitors brain activities by detecting chnages associagted with blood flow in brain areas. -Relies on blood flow in brain areas -Measures BOLD response through magnetic instead of optical methods. -Hemoglobin differs in how it responds to magnetic fields,depending on wether it has a bound oxygen molecule. -fMRI has higher penetration than NIR light, which gives fMRI greater ability to capture infromation from deep parts of the brain than fNIRS. -fMRI has a higher spatial resolution than fNIRS since the latter's spatial resolutions of fMRI and fNIRS are at equal level beacuse they both are constrained by the blood flow speed.
flaws of fMRI: 1.fMRI requires an expensive scanner to genrate magnetic fields. 2. The scanner is heavy and has poor portability.
*Note: spatial resolution: refers to how well the signal discriminates among nearby locations. Temporal resolution: refers to ther smallest time period of neural activity reliably separated out. Bandwidth: EEG(0-50Hz) vs ECoG(0-500Hz)
EOG is a technique of measuring the corneo-retinal standing potential that exists between the front and back of the human eyes. Ch.V+ & Ch.V- meaures the verical movements. Ch.H+ & Ch.H- measures the horizontal movement. -low spatial resolution: compared to other signal because we can only detect the verticle and horixontal potentials. -high temporal resolution: than neuroimaging technique because the electrical potential vary faster than metabolic feature(blood flow)
MEG is functional neuroimaging technique for mapping brain activity by recording magnetic field produced by electrical current occuring naturally in the brain,using very sensitive magnetometers like SQUIDs. -low Spatial resolution:becasue signal quality highly depends on on the mesurement factors. -High temporal resolution(>=1000Hz): because the MEG directly moniters the brain activity from the neuron level,which is in the same level mof intracortical signals. -MEG euipment is expensive and not portable
- HW has high portability with much lower price
- the temporal resolution is very high 3.EEG is relatively tolerant of subject movement and artifects which can be minimized by existing signal processing methods. 4.subject doesn't need to be exposed to high intensity (>1 tesla) magnetic fielsa. can serve subject having metal implanted in their body.
EEG means spontaneous EEG, which mesures the brain signals under a specific state without external simulation. (sleeping,mental task,fatigue stage,brain disorder,MI). -Gazing at a specific image, the visual stimuli are steady without anychange. -lower SNR & larger variation across subjects
EP or evoked responses refer to EEG signals which are evoked by a event stimulus instead of spontaneously. -higher amplitude & lower frequency as a result more *robust across subjects.
ERP - VEP,AEP,SEP,P300 SSEP - SSEP,SSVEP,SSAEP VEP - VEP,RSVP,SSVEP