The Central Nervous System Cellular Basis. Neural Communication. Major Structures. Principles & Methods.
Principles of Neural Organization Big Question #1: Representation. How is the external world coded by the brain? Big Question #2: Neural Localization. What neural structures carry out what cognitive functions? Where in the brain (what neuronal systems) mediate perception, memory, knowledge, etc.?
Principles of Neural Organization Big Question #1: Representation. How is the external world coded by the brain? Taste Space. Four distinct receptors on the tongue. Firing rate reflects strength of activation. Combination of activation = coding vector = taste. "Cognition as computation".
Principles of Neural Organization Big Question #1: Representation. How is the external world coded by the brain? Color Space. Three receptor types (cones) in the eye. Firing rate reflects strength of activation. Combination of activation = coding vector = perception of different colors. Cf. Face Space.
Principles of Neural Organization Big Question #1: Representation. How is the external world coded by the brain? Changing one rep. into another. From a 4D to a 3D vector. Effect of each input fiber (axon) on receiving cell is set by the "weight" (and polarity +/-) of its connection.
Principles of Neural Organization Big Question #2: Neural Localization. Cortical Areas. Brodmann's Cytoarchitectonics. Flechsig's Order of Myelination. Cortical Maps. The Sensory and Motor Projection Areas. Retinotopic Mapping. Flow of Information. Luria's Hierarchical Model. Felleman & van Essen's Parallel, Distributed Hierarchies.
Cytoarchitectonics / Brodmann Areas
Cytoarchitectonics / Brodmann Areas
Order of Myelination (Flechsig)
Primary Sensory and Motor Projection Areas Sensory and Motor "Homunculi"
Primary Sensory and Motor Projection Areas Sensory Homunculus Motor Homunculus The sensory & motor homunculi reveal an important function of the brain: The "mapping" of the external world into neuro-cognitive representations.
Retinotopic Mapping Autoradiograph of monkey visual cortex (bottom) showing how stimulus (top) was processed in a retinotopic (point-to-point) fashion (as if forming a 2D "map" of the image that was on the retina). Similar mapping is seen in the auditory system ("tonotopic mapping").
Luria's Hierarchal Model of Info Flow The Sensory Unit. Primary: Basic features. Secondary: Combined features. Teriary (Association): Integration with other modalities. The Motor Unit. Teriary (Association): Executive Functions (Planning). Secondary: Pre-motor. Primary: Motor (to muscles).
Cortical Hierarchies
Parallel, Distributed Hierarchies Felleman & van Essen's "circuit diagram" of the macaque visual cortex showing over 30 distinct processing areas. Note that (a) there are multiple primary (& secondary) areas working in parallel; (b) lower areas may project directly to higher areas; (c) higher areas project back to lower areas.
Methods in Neuroscience The Lesion Method. Cognition after brain damage. Transcranial Magnetic Stimulation (TMS). Electrophysiology. Electroencephalography (EEG). Event-related Potentials (ERP). Neuroimaging. Magnetic Resonance Imaging (MRI) Functional Magnetic Resonance Imaging (fmri) Positron Emission Tomography (PET).
The Lesion Method The "Lesion Method" refers to the use of brain damaged patients to understand the function of an area. If a patient cannot perform a task, the damaged area is assume to play a role in the normal performance of that task. APRAXIA disorder of movement & action. APHASIA disorder of speech. AGNOSIA disorder of object recognition. PROSOPAGNOSIA disorder of facial recognition. SPATIAL NEGLECT disorder of attention. AMNESIA disorder of memory.
The Lesion Method Split-brain patients (Sperry & Gazzaniga). Corpus Collosum
The Lesion Method Split-brain patients (Sperry & Gazzaniga). Patient fixates center dot. Words projected to opposite hemispheres. When asked what they saw, pt. says word on right but left hand picks up left-word object.
Transcranial Magnetic Stimulation (TMS) TMS disrupts neural activity, producing a "reversible lesion".
Electrophysiology ("Brain Waves") Measurement of brain's electrical activity. Typically recorded at the surface of the brain. Good temporal resolution; poor spatial resolution. EEG Trace
Event-Related Potentials (ERP) EEGs averaged over many trials
Neuroimaging Structural. X-rays & CAT scans. Magnetic Resonance Imaging (MRI). Functional. Functional Magnetic Resonance Imaging (fmri). Positron Emission Tomography (PET).
Positron Emission Tomography (PET)
Positron Emission Tomography (PET)
Magnetic Resonance Imaging (MRI) Structural Images Functional Activity (projected on structural scans)
Magnetoencephalography (MEG) Measures the magnetic fields produced by electrical brain currents using Superconducting Quantum Interference Devices (SQUIDS)
Spatial vs. Temporal Resolution
New Imaging Techniques Diffusion Tensor Imaging (DTI) Functional Near Infrared Spectroscopy (fnirs) MRI & EEG/ERP fnirs & EEG/ERP