2 Neurons. 4 The Brain: Cortex

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1 1 Neuroscience 2 Neurons output integration axon cell body, membrane potential Frontal planning control auditory episodes soma motor Temporal Parietal action language objects space vision Occipital inputs Detector dendrites synapses Neuron Neurons are detectors (e.g., smoke detector): Looking for patterns in their inputs. Target pattern is determined by weights (synapses). 3 Networks of Neurons: The Cortex 4 The Brain: Cortex Frontal planning control auditory episodes soma motor Temporal Parietal action language objects space vision Occipital Two different populations of neurons: Excitatory (glutamate): Pyramidal, Spiny stellate. Inhibitory (GABA): Chandelier, Basket... superior dorsal anterior top rostral front lateral medial lateral posterior caudal inferior back ventral bottom

2 ral Cortex 5 The Limbic System Response Monitoring Limbic System Inter-hemispheric Transfer 6 Methods: Overview How can we record activity inside the brain? M ov e m en t T o u c h Audition Spatial Processing Vision Sensory Relay Cerebral Cortex Response Mo isual Object Recognition e Cell Recording Measures correlations between stimulus/response events and neural activity. Identifies possible information processing characteristics of neurons in different brain regions. Precise Timing Directly measures neural activity Limitations Only animals Memory (hippocampus is buried inside of here) Brain Lesions General Approach Infer the function of a given area by assessing how cognition/behavior is influenced by injury to that area. Animals Experimentally induced lesions Can be anatomically precise Humans Victims of stroke, injury, disease, etc. Rarely anatomically precise 7 Methods: Overview Electrophysiology/Single Cell Recording Brain Lesions PET: Positron Emission Tomography : functional Magnetic Resonance Imaging ERP: Event Related Potentials High-level cognition (planning, control) 8 Electrophysiology/Single Cell Recording M ov e m en t T o u c h Audition Spatial Processing Visual Object Recognition Single Cell Recording Vision Measures correlations between Direct stimulus/response measure of activity. events Spatial: and individual neural activity. neurons. Temporal: millisecond. Identifies possible information processing characteristics of neurons in different brain regions. Only in animals (usually). Precise Timing Only Directly shows measures correlations. neural activity Limitations Need parallel recording. Only animals (hippocamp Gener Infe cog Anima Exp Can Huma Vic Rar

3 Broca s Area 9 Brain Lesions Infer function of damaged brain region via behavioral effects. 11 Brain Lesions Infer function of damaged brain region via behavioral effects. 10 Broca s Broca s Area vs. s Broca s Aphasia Ungrammatical, Broca s Aphasia Broca s Area Ungrammatical, but semantically appropriate but semantically words appropriate words Mostly normal Mostly normal Ungrammatical, but semantically appropriate words Ungrammatical, Mostly normal but semantically appropriate words Mostly normal Grammatical, but meaningless impaired Grammatical, but Grammatical, meaningless but meaningless impaired impaired 12 Brain Lesions: Summary Grammatical, but meaningless impaired Key problem: If P, then Q does not imply if Q, then P! If: drinking beer, then: must be 21(!) If: 21, then: drinking beer!? not necessarily If: broca s=syntax, then: broca s lesion = bad syntax. If: bad syntax, then: broca s=syntax!? not necessarily! Shows causal role of brain area. Can make highly accurate lesions in animals. Brain may not be modular: damage = complex effects. Lesions in humans are very messy.

4 antics Assumes everything else works normally. Indirect effects on other interconnected areas? In humans Uncontrolled Over-reliant on case studies 13 PET: Positron Emission Tomography 14 A PET Study oimaging ography (PET) esonance Imaging entials (ERP) Positron Emission Tomography Measures blood flow = indirect measure of neural activity. Need to subtract away a control condition to get results.. What you see is very much a function of this control. Assumes pure insertion : speaking + generating - speaking = generating. 15 PET: Summary 16 MRI & Non-invasive: shows function of normal brain. Gives big picture view of where cognition happens. Indirect measure: blood flow. Correlational. Brain may not be modular: pure insertion? Measures differences in magnetic properties: Structural = grey vs. white (water content): good for lesion loc. Functional = oxygenated blood is magnetic! Has worse spatial, temporal resolution than.

5 17 Study of Motion Processing in MT ctional Magnetic Resonance Functional Imaging Magnetic () Resonance Imaging () Functional Magnetic Resonance Functional Imaging Magnetic () Resonance Imaging () 18 Study: Functional on Structural Temporal dynamics of the BOLD response for static and moving visual stimuli (vs. fixation) in V1 and MT: MT is selective for motion! Same as PET 19 Summary Non-invasive: shows function of normal brain. Same as PET Advantages compared to PET Advantages compared to PET Better spatial resolution (depends on Better magnet spatial strength) resolution (depends on magnet strength) Better temporal resolution (about 6 sec) Better temporal resolution (about 6 sec) Reliable images can be obtained in single Reliable subjects images can be obtained in single subjects Less expensive and less invasive Less expensive and less invasive Limitations Limitations Measures blood oxygen level. Measures blood oxygen level. Gives big picture view of where cognition happens. Indirect measure of neural activity Indirect measure of neural activity Temporal Resolution Still Too Temporal Coarse Resolution Still Too Coarse Averages across 1 minute of activity Averages across 1 minute of activity 20 Converging Methods Akinetopsia Brain injury causes a selective deficit in motion perception. Damage to area MT Consistent with Same as PET Advantages c Better spati Better temp Reliable im Less expen Limitations Measures blo Indirect me Correlationa Temporal Re Averages a Electroenceph Indirect measure: blood flow. Correlational. Brain may not be modular: pure insertion? Has better spatial, temporal resolution than PET. Lesions to MT also produce motion processing impairments. Using multiple methods reduces limitations of each! Event Related Potentials (ERP) ERP Averaging One Trial

6 21 EEG: Electrical Activity in the Scalp Electroencephalogram (EEG) 22 ERP: Event Event-Related Related Electrical Potentials Activity (ERP) (Averaged) E A Electroencephalogram (EEG) s (ERP) ERP Averaging One Trial ERP Signal < Noise 23 ERP: Event-Related Electrical Activity (Averaged) ERP Averaging One Trial ERP Signal < Noise 24 ERP: Summary Non-invasive: shows function of normal brain. Gives big picture view of when/where cognition happens. Is a direct measure of neural activity. Many Trials Many Trials ERP Signal > Noise ERP Signal > Noise Has excellent temporal resolution relative to, PET. Correlational. Brain may not be modular: pure insertion? Spatial localization is terrible.

7 130 ms 90 ms 25 Overall Summary Constraints & Convergence Each method of cognitive neuroscience has strengths and weaknesses. When multiple methods are applied to the same problem, convergent information is useful for understanding how cognitive processes are realized within the brain.