VISUAL CORTICAL PLASTICITY OCULAR DOMINANCE AND OTHER VARIETIES REVIEW OF HIPPOCAMPAL LTP 1
when an axon of cell A is near enough to excite a cell B and repeatedly and consistently takes part in firing it, some growth or metabolic change takes place such that A s efficiency, as one of the cells firing B, is increased. -Donald Hebb, 1949 i.e., Fire together, Wire together Use it or lose it ACTIVITY-DEPENDENT SYNAPTIC PLASTICITY Input Layer Competition or Cooperation? Target 2
PROPERTIES OF LTP IN CA1 3
Whitlock et al. show mimicry and occlusion 4
OCULAR DOMINANCE PLASTICITY CRITICAL PERIOD REGULATION OF PLASTICITY VISUAL PATHWAYS 5
Visual map refinement: Neighboring neurons in the retinotopic map fire together and wire together Retina SC Retina SC BINOCULAR VISION 6
OCULAR DOMINANCE COLUMN ASSAYS Development of Ocular Dominance Columns-Anatomy 7
Development of Ocular Dominance Columns-Physiology from Sanes et al. 2005 ACTIVITY-DEPENDENCE 8
2/7/2015 SPONTANEOUS RETINAL ACTIVITY 3-eyed frogs: induction of OD columns from Constantine-Paton et al. 1978 9
REPRESENTATION OF HEBB'S POSTULATE AS IT MIGHT OPERATE DURING DEVELOPMENT OF THE VISUAL SYSTEM EFFECTS OF MONOCULAR DEPRIVATION ON OD COLUMNS OCULAR DOMINANCE PLASTICITY 10
Binocular deprivation has a minor effect- Evidence for interocular competition from Sanes et al. 2005 Strabismus prevents binocularity- Interocular coordination is necessary from Sanes et al. 2005 11
OCULAR DOMINANCE PLASTICITY EXHIBITS A CRITICAL PERIOD from Purves et al. 2004 CRITICAL PERIOD FOR OD PLASTICITY Juvenile Adult 12
MECHANISM: LTP/LTD? Common forms of synaptic plasticity in slices of adult rat hippocampus (A) and adult rat visual cortex (B). Bear M PNAS 1996;93:13453-13459 BCM Sliding Threshold Model Bear M PNAS 1996;93:13453-13459 1996 by National Academy of Sciences 13
HEBBIAN PLASTICITY IN V1 Kirkwood A, Bear MF. Hebbian synapses in visual cortex. J Neurosci. 1994 Kirkwood A 1, Lee HK, Bear MF. Co-regulation of longterm potentiation and experience-dependent synaptic plasticity in visual cortex by age and experience. Nature. 1995 SUPPORTING EVIDENCE NMDAR-dependence 2B 2A Occlusion Critical period timing matches 14
LTP/LTD in Sensory Cortex Exhibits a Critical Period from Sanes et al. 2005 LTP in Visual Cortex is Disrupted by NMDAR Blockade Hensch TK et al. J Neurosci 1998 15
DO NMDA RECEPTORS HAVE A CRITICAL FUNCTION IN VISUAL CORTICAL PLASTICITY? THE OPERATION OF NMDA RECEPTORS IS DIFFERENT IN THE INTACT ANIMAL THAN IN VITRO. FOR EXAMPLE, NMDA RECEPTORS ARE ACTIVATED AT LOW LEVELS OF SENSORY INPUT IN INTACT ANIMALS BUT ONLY BY HIGH LEVELS OF INPUT IN SLICE PREPARATIONS. RECENT RESULTS SUGGEST THAT A RE-EVALUATION OF THE ROLE OF NMDA RECEPTORS IN NEOCORTICAL PLASTICITY IS REQUIRED. FOX K, DAW NW. TRENDS NEUROSCI. 1993 WHAT CAUSES THE CRITICAL PERIOD TO OPEN AND CLOSE? HOW COULD ADULT PLASTICITY BE PROMOTED? 16
CRITICAL PERIODS AND GABA GABA-AR function is necessary CRITICAL PERIODS AND GABA Toyoizumi T 1, Miyamoto H, Yazaki-Sugiyama Y, Atapour N, Hensch TK, Miller KD. A theory of the transition to critical period plasticity: inhibition selectively suppresses spontaneous activity. Neuron 2013 What causes critical periods (CPs) to open? For the best-studied case, ocular dominance plasticity in primary visual cortex in response to monocular deprivation (MD), the maturation of inhibition is necessary and sufficient. How does inhibition open the CP? We present a theory: the transition from pre-cp to CP plasticity arises because inhibition preferentially suppresses responses to spontaneous relative to visually driven input activity, switching learning cues from internal to external sources. This differs from previous proposals in (1) arguing that the CP can open without changes in plasticity mechanisms when activity patterns become more sensitive to sensory experience through circuit development, and (2) explaining not simply a transition from no plasticity to plasticity, but a change in outcome of MD-induced plasticity from pre-cp to CP. More broadly, hierarchical organization of sensory-motor pathways may develop through a cascade of CPs induced as circuit maturation progresses from "lower" to "higher" cortical areas. 17
PARVALBUMIN+ GABA+ BASKET NEURONS Bistable Parvalbumin Circuits Pivotal for Brain Plasticity Figure 1 Bistable Network Configurations of PV-Expressing Neurons in Brain Plasticity (A) Network configurations favoring plasticity. (B) Network configurations favoring stability Takao K. Hensch TK Cell 2014 18
Selective Rearing Biases Response Properties 19
PLASTICITY IN THE AUDITORY PATHWAY Selective rearing experiments in the auditory system from Sanes et al. 2005 20
Barn Owls model system to study mechanisms of sound localization and neural plasticity in the midbrain. Barn Owl The Silent Hunter 21
Barn owl sound localization assay Azimuth - ITD; Elevation - IID 22
Barn owl Azimuth - ITD; Elevation - IID Barn owl space map in ICx 23
Barn owl sound localization: Parallel pathways for IID and ITD 24
Juvenile Plasticity- Behavior Juvenile Plasticity- Electrophysiology 25
Juvenile Plasticity- Anatomy Instructive Signals to ICx from ICc, Tectum 26
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Sensitive period Physiological traces of learning in prism-reared adults Effect of age and prior experience on ITD map plasticity ANATOMICAL TRACES OF LEARNING IN PRISM-REARED ADULTS New terminals Shifted neurons Prism-induced shift Retrograde tracer Anterograde tracer Linkenhoker BA, von der Ohe CG, Knudsen EI. Anatomical traces of juvenile learning in the auditory system of adult barn owls. Nat Neurosci. 2005 28
Incremental Training in Adults Linkenhoker BA, Knudsen EI. Incremental training increases the plasticity of the auditory space map in adult barn owls. Nature 2002 Incremental Training in Adults 29
FACILITATION BY HUNTING Figure 1. Effect of prism experience with and without hunting on ITD tuning in the OT of an adult barn owl. Bergan, J. F. et al. J. Neurosci. 2005 [arrows in B, D, E indicate expected ITD shift] Copyright 2005 Society for Neuroscience PLASTICITY IN THE SOMATOSENSORY PATHWAY 30
Somatotopic maps Rat Somatosensory Pathway After Woolsey & van der Loos, 1970 31
BARREL CORTEX PLASTICITY Normal Spared C and β Lesion C row Woolsey & van der Loos, Science, 1973 BARREL CORTEX PLASTICITY Fig. 4. Supernumerary whiskers and extra barrels in an Ad-cShh-infected embryo. From Ohsaki et al 2002 Devel Brain ReS 32
Somatotopic map plasticity is Hebbian 33
Somatotopy matches lifestyle 34
2/7/2015 VISUAL ACUITY Visual Stimulation and Single Unit Recording 35
Visual Modules 36