Cracking The Neural Code (Week 1) Flashcards
2 main types of brain cells
neurons and glia
neurons function
signal changes in the environment, internal states and plans of action
glia functions
regulate chemical context of space between cells (extracellular spaces) and insulate axons of neurons
what are the main cells types representing information
neurons
what types of glial cells regulate chemical context of space between cells (extracellular spaces) ?
astrocytes
what type of glial cells insulate axons of neurons
oligodendrocytes and Schwann Cells
are there more glial cells or neurons in the brain
glia
dendrite function
connect at synapses with other neurons to receive information from them ; post synaptic part of neuron
what is the cell membrane of a neuron
phospholipid bilayer
axon function
provide input to other neurons through electrical pulses/ spikes
axon hillock
site where action potential is generated
axon terminal
part of axon that is part of synapse; pre synaptic part of synapse
cell body (soma) function
gene expression (nucleus), protein synthesis (ribosomes, rough ER), protein sorting(smooth er and golgi), cellular respiration (mitochondria)
important ions for neuron signaling
K+, Na+, Ca2+, Cl-
electric potential
energy needed to move a positive ion towards positive source
when does a positive ion have more stored energy/electric potential?
when it is closer to the positive source
what does positive ion have less potential energy/ loose potential energy
as it moves towards the negative source of the electric field
what ions are more abundant outside of the cell
Na+
what ions are more abundant inside of the cell
K+
what allows ions to move through membrane
ion channel (peptide subunit) facilitates membrane transport due to selectively permeable membrane
what is resting membrane potential
-65 mV; reflects charge separation across cell membrane
why is the resting potential more negative inside of the cell
leaky K+ channels move K+ out of the cell which makes the inside of the cell less positive
depolarization
membrane potential of cell becomes less negative
hyperpolarization
membrane potential of cell becomes more negative
what factors determine ion movement across membrane
concentration gradient and electric potential difference/membrane potential
equilibrium potential
E ion: electric potential difference that exactly balances ion concentration gradient
what are the 2 classes of ion channels
voltage gated ion channels and ligand gated ion channels
ligand gated ion channels
ligand binds -> structural change
*GABA receptor: lets in anions
*glutamate receptor: lets in cations
voltage gated ion channels
channel opens due to change in membrane potentials (closed at rest)
membrane potential threshold
the level at which an action potential is triggered in a cell
what triggers an action potential
Na+ moves into the cell and depolarizes it
how how long is channel open during process of firing an action potential
about 1 millisecond; after channels closes ->inactivated (absolute refractory period)
stages of firing an action potential
1) resting
2) rising phase (depolarization; Na+ into cell)
3) overshoot (spike)
4) falling phase (hyperpolarization; Na+ channels close and K+ channels open)
5) undershoot (refractory period)
6) resting; re establish conc gradient
how is concentration gradient re established in cell
sodium potassium pump
where does the action potential travel?
from axon hillock to axon terminal
how is action potential regenerated down axon?
Na+ influx of the action potential depolarizes membrane ahead of the threshold -> chain reaction of regenerating action potential
2 types of neruons
pyramidal neurons (dendrites) and sensory neurons
2 types of single neuron/ single unit recordings
extracellular and intracellular recordings
intracellular recordings
intracellular electrode that measure action potentials from targeted cell
extracellular recordings
electrode in extracellular space pick up spikes from surrounding cell/cells
what does a larger amplitude of spike mean in extracellular recordings
that spike came from a closer neuron
how do you differentiate between neurons in extracellular recording data
by shape and amplitude
what are local field potentials (LFP)
subthreshold fluxuations : how many oscillations in the membrane potential of neurons that occur below the firing threshold
how many signals can a classical electrode measure
only signals from a few cells
matrix electrodes
grids of tiny electrodes that can be used to measure or deliver neural signals; measures community of cells
laminar probe
probe with multiple vertical electrode contacts; can record from all 6 layers of the cerebral cortex
can patients feel the electrodes?
no because there are no pain receptors in the brain
what kind of recordings are used in research more often
extracellular recordings; because more recording stability and easier for human behavioral experiment
neuropixils probe
a new technology that has more electrode contacts in only 1cm
impedance
a measure of resistant plus electroes ability to store charge (capacitance)
how does size impact impedance
smaller the electrode contract, the higher the impedance
what comes from higher impedance/ resistance
harder for currents to flow through, meaning we can isolate certain neurons and get a localized signal
consequences of larger exposed metal contact
low impedance meaning its harder to isolate individual neurons
LFP recordings from extracellular depth electrode
reflects ~1,000 cells
*signals derived within 250 microns of electrode tip
LFP recordings from ECoG
intracranial recordings for epilepsy patients; pre surgery approach to localize seizure/ abnormal vs normal brain activity
*electrodes on exposed brain surface (subdural; invasive)
what do EEG signals meausre
sum of synchronized activity of neurons with similar spatial orientation
how many cells to EEG signals reflect
100,000-1,000,000 cells
EEG electrode arrangement
electrodes above scalp usually on cap; non invasive technique
*good temporal resolution
EEG disadvantages
- skull smears signal -> degrade source localization
-deep brain structures inaccessible
-poor spatial resolution
temporal resolution
ability to detect changes in brain activity over time
spatial resolution
the ability of a neuroimaging technique to distinguish between two closely located points in the brain
- lower spatial resolution = more blurred image
how are FMRI signals produced
magnetic field applied to excite H atoms, H atoms align with magnetic field then fall to release energy; emitted radio frequency signal measured
**measures brain activity indirectly by detecting changes in blood flow (the Blood Oxygen Level Dependent, or BOLD signal)
FMRI spatial
-better spatial resolution than EEG
FMRI temporal resolution
bad temporal resolution because brain activity measured indirectly by BOLD signal; slower than neuronal activity so only can have a measurement every 2 seconds
are FMRI signals more correlated with spikes or LFP’s
LFP
how are FMRI changes in size of signals measured
brain is divided into tiny squares called voxels and percent changes in brain activity graphed
single unit recording;
invasive, # of cells, spatial resolution, temporal resolution
invasive
1 cell
high spatial resolution (<30um)
high temporal resolution(<1ms)
LFP;
invasive, # of cells, spatial resolution, temporal resolution
invasive
~1000 cells
less spatial resolution than single unity (250um)
good temporal resolution (<1ms)
EEG:
invasive, # of cells, spatial resolution, temporal resolution
non invasive
over 1,000,000 cells
bad spatial resolution (>5mm^2)
good temporal resolution (<1ms)
FMRI:
invasive, # of cells, spatial resolution, temporal resolution
non invasive
500,000 cells
good spatial resolution (2x2x2mm^3)
bad temporal resolution (2s)
spike rate code
number of brain spikes from 1 cell in a given interval
effect of increasing stimulus intensity
increasing number of spikes up to a certain point
pooled response code
number of spikes from multiple cells in a given interval; measures population of neurons
why is pooled response code more reliable
counteracts variability of single cell response and reduces noise
labeled-line code
a notion to express which neurons are firing and the number of spikes for each one: vector formed from joint firing of multiple neurons
ex) (cell 1 # of neurons, cell 2 # of neurons)
2 types of neural codes
spike timing codes and spike rate codes
spike pattern codes
temporal pattern of spikes in a given time interval; divide each time interval into smaller bits
spike rate codes
relies on brain’s internal clock (network of neurons that osalate together) to time spikes
2 steps in decoding neural activity
training step and test step
training step: decoding neural activity
use subset of data to train classifier to help learn relationship between pattern of neural activity and experimental conditions
*classifier can be linear or nonlinear
test step: decoding neural activity
predict catagores new data belongs to based on classifier
how to increase accuracy in decoding neural activity
increase number of sites
how do neural prosthese work
EEG sends signals to BCI (brain computer interface) which decodes the neural information and feeds it into prostatic to signal muscle activity
what neural prosthesis are being developed
eeg based models and intracranial implants to record spikes and LFP’s (which would increase decoding accuracy)
