GOAL OF THE COURSE: to understand how we get mind from brain – difficult problem to solveCognition (perception, memory, social behavior, etc.) in terms of neuronal activityMultiple levels of analysis:BehaviorSpeed, accuracy, and confusions of discrimination/recognition1/10th of a secondSpontaneous categories/preferences that people manifestBrain as a system (real estate)What brain loci/circuits are activated in a certain behavior? (fMRI)Effects of restrictive lesionsNeural CodingSingle unit activity – what are individual neurons doing?Population code – 10’s of thousands of millions neurons (theory, neutral net model)Lumping together groups of neurons and coming up with something that they can do?CPU: can’t store two things in one locationBiological memory: stored in neural tissue, don’t have to erase what we already have – new material gets integrated into networkHippocampus allows new experiences to be integrated with old experiences by adjusting synapse strengthDevelopment (throughout all levels of life)How genetics and experience build a brainDiverse methodologies to try and answer how mind is separate from brainBehavioral and psychophysical testingAnalysis of lesions and genetic variation in patient populationfMRI and optical imagingSingle unit recording – mesh electrode plate on brain and can measure/stimulate brainNeurotransmitter and hormone levelComputational analysisCerebral cortex does sensory input and outputMacaque Cortex-ventral pathway for recognitionCan pick up item but cannot tell you what it isDorsal pathway for motorLesion in dorsal pathway – cannot pick up an item but can tell you what it isFour lobes (occipital, temporal, parietal, frontal)Flattened out, each hemisphere equivalent to two medium (36cm diameter) pizzas100 billion neuronsEach neuron in visual cortex receives inputs from 2000-10000 other neurons: needs ~200 neurons firing in one dendrite of postsynaptic neuron in less than 2ms = FIRE~100,000 neurons/mm cubed~800 million synapses/mm cubed3km axons per mm cubedBrain is washed in GABA inhibitory bath, conserving energy, signals can be selected, and sparse neural codes = NO SEIZURESCortex and Vision50% of macaque and ~50% of cortex either exclusively or partially devoted to vision (27% of whole brain)Local cortical modules are each performing a different function for visionSubmodules are in an area (eg. Visual recognition has subregions for faces, places, tools, colors)Why use modules? Neurons need to interact with each other, so bring them together so long distances aren’t needed = less energy and less myelinationEfficient packaging/compartmentalization minimizes fiber length, volume, energy consumption – does it fasterDoes the nervous system minimize fiber length?Christopher Cherniak (1994) – realized nemotode c. elegans could analyze neuron efficiency because we know the complete nervous system and ganglia are arranged linearlyTraveling salesman problem – what is the most efficient route?C. elegans have optimal arrangement for minimizing axon lengthNext best is only .1% worseHow do the neurons know where to go?C. elegans is too close to big bang so trial and error isn’t how the neuron position adaptedProcess:Target neurons signal when they need another neuron to attach – chemical attractor (progenitor neuron)Recent: cooperation and competition from recently generated neuronsDo we see evidence of component optimization in mammalian organization? Yes.Areas that are spatially contiguous have high connectivity (seen in visual and motor areas)Limiting factor seems to be spatial contiguity: some noncontiguous areas are also highly connectedCorpus callosum counters “efficiency” model –wtf?Cherniak deduced: C. elegans are social, and some would eat by themselves and some would eat together (social difference – eating together, is there a genetic source of this behavioral difference?)Big developmental questions:How does a brain build itself?How does the mind build itself?How are the effects of experience incorporated?Brain:Glial cells send signals into cells that will ultimately become cortex. Once strands go up, then cells are born that will be activated and crawl along fiber into cortex – build a column of cells (Radial Unit Model – Pasco Rakic in 1988)Over time, 6 layer cortex is builtTop most layer is newest layer addedPruning: cell deathA large number of neurons in the cortex die over time – purposeful reduction in number of cellsNo, we do not become dumberYou are getting rid of neurons that aren’t doing much for you, and with new space available, you sprout a large number of dendrites = dendrites, up until 20’sChimp prefrontal cortex – more neurons per cubic inch than humans, but humans have more dendritesSynaptogenesis, synaptic pruningSensorimotor cortex, then parietal/temporal cortex, then prefrontal cortex are myelinated and etc. in that orderHence why decision making is hindered/limited until 20’s, since prefrontal cortex is myelinated lastBehavior:Broadbent’s information flowchart of human performance as overview of behavior (1958)SensesShort term memory filter (rehearsal loop with limited capacity channel, not all information retained)Limited capacity channel either goes to long term memory or response selectionNeed to go through limited capacity channel to long term memoryChannel is the same channel for external sensory input as well as internal sensory input (daydreaming/imagination)After practicing long term memory, response occursRehearsal loop: look up phone number and keep rehearsing it and then type in number, but if someone asks you what time it is, you forget it (distraction)High frequency – higher auditory spikesLow frequency – lower auditory spikesTonotopic maps in cortex through fMRIReceptive field for auditory neuron is tuned to a particular position, size (frequency), orientation (direction)Neurons will fire when stimulated with appropriate stimulus (stimulus must match preferred scale of cell)Mexican hat tuning profile - sound ?High bandpass spatial frequency – sharp, outlineLow bandpass spatial frequency – fuzzyDifferent scales, and then combined to form picture we knowPatient DF – can use hands, visual expression is not okayFound in shower in a coma – hypoxia (lack of oxygen) from CO poisoningWhen she woke up, she couldn’t seeWhen boyfriend came in, didn’t recognize himIf person spoke, she knew who it wasShe could see things (like a fork) but