Voorbereiding Lecture 8
Learning Objectives Chapter 6:
1. Contrast electroencephalography(EEG) with functional magnetic resonance imaging (fMRI).
2. Compare transcranial magnetic stimulation (TMS) with electrical stimulation techniques.
3. Describe the anatomy of a typical neuron.
4. Identify major anatomical brain regions.
5. Distinguish the dorsal and ventral visual pathways in the brain.
6. Define distributed coding among neurons in cortex.
7. Summarize Hebbian learning among neurons and long-term potentiation,
8. Describe the role of the hippocampus in memory
Neuroscience = Study of nervous system anatomy and physiology (structure & function in humans and
other animals)
Neuroscience provides knowledge, serves as foundation, understanding how cognitive operations are
carried out (Implementational description, on which we can base algorithmic and computational
description)
Cognitive neuroscience = Integration biology and cognition, goal; analyze/relate structures and
physiological processes to cognitive processes
Methodology in neuroscience
1) Techniques for the study of brain damage
2) Brain recording methods (EEG, ERP)
3
3) Positron emission Tomography (PET) brain
4) Functional Magnetic Resonance Imaging (FMRI) recording methods
5) Magnetoencephalography (MEG)
6) Knife-Edge scanning Microscope
7) Electrode simulation brain stimulation
techniques
8) Transcanial Magnetic Stimulation
9) Optogenetics
⑪
Case study: study of damaged brain (as result of an accident)
Lesion study: precise destruction of a specific brain region in an animal to examine resulting behavior deficits
Critique: Areas of the brain are interdependent (Effects of damage to one area -> a variety of functional
interpretations, ex. area could be info-processing center or region through which neural pathways pass
Brain recording Methods
tradit onal
Single cell recording = Insertion of very fine microelectrode into a single neuron (or fluid adjacent to it)
-> change in that cells electrical conductivity/rate of firing can be measured
Multiunit recording = larger electrode is used to measure collective electrical activity of a group of neurons
Critique: does not inform us about the more global brain activity
② EEG = recording of the brain’s gross electrical action in the form of electric wave patterns at diff. frequencies
When used to measure subject’s brain activity in response to experience of a stimulus event, the resulting
waves are = ERPs (event-related potentials)
Pro: can detect fine-grain changes in cogn. processes (in ms.)
Critique: Spatial resolution is coarse (only shows activity in large brain areas, ex. diff. cortical lobes)
,③
PET = measures blood flow in the brain while participant carries out cognitive task (through use of radioactive
isotopes attached to carrier substances, ex. glucose or O2 molecules)
Brain areas that are more active will show greater rCBF (regional cerebral blood flow) Activity is measured
using device that counts positron particles that are emitted by isotopes
Pro: pretty good spatial resolution (able to monitor locational changes in brain activity to within mm)
Critique: cannot show rapid changes in brain activity (like EEG can)
radioactive isotopes are expensive and frequent exposure is risky
⑭
fMRI = participant is placed inside tube that contains powerful magnet, video images show dynamic
changes in (brain) activity over time
Process: Protons present everywhere in the body, align themselves in magnet field->radio wave pulse is
applied->radio signals are bounced back & picked up by detector unit->reflected signals convert to video
Like PET scans, fMRI scans detect alterations in local blood flow and oxygen
Pro: fMRI provides better spatial resolution than PET (without risks of radioactive isotopes)
Critique: unable to detect rapid changes (on time scale of ms like in EEG)
⑤ Electric fields that active neurons generate also have magnetic properties
In MEG = these magnetic fields are measured to determine patterns of brain activity (Helmet, 3D video)
Pro: Good spatial and temporal resolution
⑥ KESM = Device consisting of diamond tipped knife that slices through tissue->white light source illuminates
tissue reflecting an image to a camera->video processed by a computer system-> 3D reconstruction down to
cellular level
Brain stimulation techniques
Activation of a specific brain area via electrical or magnetic simulation
⑦
Electrical simulation = an electrical current is passed through a bipolar electrode->neurons of a localized
area of brain tissue becomes active
⑧ TMS = Device with wire coil placed over person’s head. Electrical current is passed through coil inducing
magnetic field->field causes neurons to fire
⑨ Optogenetics = Control/stimulation of neurons using light (use of proteins called Opsins that
become sensitive to light to modify neuron activity as it is happening)
Anatomy < neuron-brain)
①
① Neurons = microscopic basis of the brain, individual functional units that perform computations, it’s
purpose is to conduct a message in the form of an electrical impulse
It sums excitatory (positive) and inhibitory (negative) signals to determine whether it sends out a message
Messages are received by dendrites->passed along cell body->signals from other cells converge at the
axon hillock (here the sum takes place)->fire if inputs exceed threshold of excitation
, If threshold is met; electrical signal called action potential is initiated->action potential propagates down
the axon, which ends in a number of terminal buttons that meet dendrites of other neurons
There is a gap here; synaptic cleft->neurotransmitters complete transmission of signal across synapse
(attaches to receptor molecule)->receptors contribute to formation of new signal
② Brain regions
Dorsal: toward the top Ventral: toward the bottom
Anterior: regions toward front Posterior: regions toward back
Medial: regions toward interior Lateral: regions near outer surface
The cortex is divided into 2 halves/cerebral hemispheres
Info is transferred between hemispheres via a bundle of connecting axons; corpus callosum, in between
there’s a cleft; fissure, smaller such separation; sulcus (separates folds of tissue), single ridge; gyrus
L = analytical, serial, logical reasoning, language
R = synthetic, parallel, relational thought processes, spatial ability
Lobes decision
Frontal lobe: Anterior- reasoning, planning, problem solving, language production
Temporal lobe: Ventral- auditory processing, language comprehension, pattern- & visual object recognition
Parietal lobe: Posterior- governs aspects of visual attention & visuospatial processing
Occipital lobe: visual info begins to undergo extensive processing
Anterior to the central fissure is the precentral gyrus; primary motor cortex/cortical homunculus (electrical
stimulation provokes muscular contraction)
Posterior to the primary motor cortex lies the primary somatosensory cortex (electrical simulation triggers
perception of touch sensation from corresponding body part)
Topography = stimuli near each other activate neurons near each other
Info received right or left half of the body is mapped onto the opposite or contralateral side of the brain (so
info is not processed on the same, ipsilateral, side)
Neuroscience Visual object
recognition
:
Visual system breaks objects down into their parts; visual inputs undergo preliminary processing in the
primary visual cortex (occipital)
Partitioning of visual input into separate streams;
Dorsal visual pathway: travels upward to parietal lobe, where info about motion & location is extracted who
Ventral visual pathway: travels downward to temporal lobe, carries data about color & form-what
Visual Agnosias: inability to recognize visual objects, pattern recognition disorder
Damage: Regions in ventral visual pathway
-
Apperceptive Agnosia: unable to assemble parts/features into meaningful whole (damage: occipital lobe)
Disruption of formation of an object representation/perceptual grouping mechanism—>lower level
~
Associative Agnosia: perceive wholes, trouble assigning name to it (damage: connections that enable
formation of object representations; temporal lobe)
Disruption of ability to categorize/identity —>higher level
Perceptual categorization deficit: difficulty recognizing objects when viewed from unusual angles or lit
unevenly (damage: right hemisphere, especially right parietal lobe)
Face perception; Prosopagnosia: inability to recognize/discriminate faces (type of associative agnosia)
Sparse distributed coding: small set of neurons are highly selective to respond to a particular face
Localist coding (single cell fires in response to presence of particular face) is unlikely
Distributed coding specific face is coded for by specific pattern of activation among a group of cells
In human beings ‘face cells’: FFA (Fusiform Face Area) in medial temporal lobe-> processes face info
