Strengthening of Horizontal Cortical Connections Following Skill Learning M.S. Rioult-Pedotti, D. Friedman, G. Hess & J.P. Donoghue Presented by Group B5 Nidhi Bhushan, Marry Fernandez, Amina Nawaz, Rachel Wallace and Rory Wasserman

Presentation Outline  Background Information  Aims of Study  Methods and Procedures  Results & Conclusions  Significance of Study  Background Information  Aims of Study  Methods and Procedures  Results & Conclusions  Significance of Study

Background Information BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Tanaka J, Horiike Y, Matsuzaki M, Miyazaki T, Ellis- Davies GCR, Kasai H Protein synthesis and neurotrophin-dependent structural plasticity of single dendritic spines. Science 310:1683–6 Nihdi  LTP  the increasing sensitivity of synapses over time, producing a larger postsynaptic output  Shown to result in growth of new, rapidly functional filipodia/spines  Learning & memory  Synaptic plasticity  LTP  the increasing sensitivity of synapses over time, producing a larger postsynaptic output  Shown to result in growth of new, rapidly functional filipodia/spines  Learning & memory  Synaptic plasticity

Background Information BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Nidhi  M1: generates neural impulses to control execution of movement  Horizontal connections between layer II and III capable of LTP  Suggests LTP can modify horizontal connection strength as a new motor skill is learnt  M1: generates neural impulses to control execution of movement  Horizontal connections between layer II and III capable of LTP  Suggests LTP can modify horizontal connection strength as a new motor skill is learnt

History of Topic Charles Sherrington - Term “Synapse” Ramon y Cajal - Synaptic ConnectionPavlov - Classical Conditioning Donald Hebb - Fundalmental Associative Mechanism Terje Lomo - Experimentally discovered LTP Richard Morris - 5 Fundamental Properties of LTP Donoghue, et al. - Acquisition of Motor Behaviour Charles Sherrington - Term “Synapse” Ramon y Cajal - Synaptic ConnectionPavlov - Classical Conditioning Donald Hebb - Fundalmental Associative Mechanism Terje Lomo - Experimentally discovered LTP Richard Morris - 5 Fundamental Properties of LTP Donoghue, et al. - Acquisition of Motor Behaviour BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rachel Textbook cite needed

Purpose of Study BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rachel  Researchers claimed that there was no previous studies explicitly showing:  M1 circuitry changes with learning  Evidence of physical modifications of neurons i.e. increasing dendretic spines really do improve cortical connections  LTP type mechanisms are used to acquire new motor skills  Researchers claimed that there was no previous studies explicitly showing:  M1 circuitry changes with learning  Evidence of physical modifications of neurons i.e. increasing dendretic spines really do improve cortical connections  LTP type mechanisms are used to acquire new motor skills Rioult-Pedotti, M.S., Friedman, D., Hess, G. and Donghue, J.P. (1998). Strengthening of horizontal cortical connections following skill learning. Nature Neuroscience 1(3),

Background Information BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rachel  What is a Field Potential?  An electrical recording visually demonstrating the electrical connectivity between synapses  Extracellular EPSP (excitatory pre-synaptic potential) field potential demonstrate the strength of that cell with the next horizontal intracortical cell as it is thought that learning is accompanied by changes in the strength of those very connections  What is a Field Potential?  An electrical recording visually demonstrating the electrical connectivity between synapses  Extracellular EPSP (excitatory pre-synaptic potential) field potential demonstrate the strength of that cell with the next horizontal intracortical cell as it is thought that learning is accompanied by changes in the strength of those very connections Rioult-Pedotti, M.S., Friedman, D., Hess, G. and Donghue, J.P. (1994). Long-term potentiation of horizontal connections provides a mechanism to reorganize cortical motor maps. Journal of Neurophysiology 71(6),

Aim of Study BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rachel  Aim  Discover empirical evidence that when learning a new motor skill cortical synapses alter and strengthen their connections  Aim  Discover empirical evidence that when learning a new motor skill cortical synapses alter and strengthen their connections Rioult-Pedotti, M.S., Friedman, D., Hess, G. and Donghue, J.P. (1998). Strengthening of horizontal cortical connections following skill learning. Nature Neuroscience 1(3),

Experiment One BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Amina  Investigated relationship between acquisition of new motor behaviour and horizontal cortical connection strength  Rats were trained in a skill reaching task involving only one forelimb over 3 to 5 days  Two sets of controls were used: paired and unpaired  Investigated relationship between acquisition of new motor behaviour and horizontal cortical connection strength  Rats were trained in a skill reaching task involving only one forelimb over 3 to 5 days  Two sets of controls were used: paired and unpaired UNTRAINED

Experiment One BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Amina Trained skill: reaching for food pellet task

Experiment One BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Amina  Horizontal cortical connection strength was measured using coronal brain slices of both hemispheres  Trained M1: hemisphere contralateral to trained forelimb  Untrained M1: hemisphere contralateral to untrained forelimb  Controls: the two hemispheres were termed "Left M1" and "Right M1"  Horizontal cortical connection strength was measured using coronal brain slices of both hemispheres  Trained M1: hemisphere contralateral to trained forelimb  Untrained M1: hemisphere contralateral to untrained forelimb  Controls: the two hemispheres were termed "Left M1" and "Right M1" LeftRight

Experiment One BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Amina  Symmetrically-placed stimulating and recording microelectrodes in layer II/III Horizontal Connections measured field potential  Compared amplitudes of field potentials in each hemisphere, for both forelimb and hindlimb regions  Symmetrically-placed stimulating and recording microelectrodes in layer II/III Horizontal Connections measured field potential  Compared amplitudes of field potentials in each hemisphere, for both forelimb and hindlimb regions

BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Amina 1) Brain slices containing the Primary Motor Cortex (M1) 2) Devices were placed accordingly:  Recording Devices: Glass micropipettes within the same relative receptor field in the II/III layer  Stimulating Devices: Concentric bipolar stimulating electrodes placed on either side of the recording electrodes 1) Brain slices containing the Primary Motor Cortex (M1) 2) Devices were placed accordingly:  Recording Devices: Glass micropipettes within the same relative receptor field in the II/III layer  Stimulating Devices: Concentric bipolar stimulating electrodes placed on either side of the recording electrodes Measuring Strength of Cortical Connections Rioult-Pedotti, M.S., Friedman, D., Hess, G. and Donghue, J.P. (1998). Strengthening of horizontal cortical connections following skill learning. Nature Neuroscience 1(3),

Measuring Strength of Cortical Connections BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Amina 3) Currents were delivered through the stimulating devices exciting the receptor cell 4) Field potentials were measured and their amplitudes were compared to determine relative strengths 3) Currents were delivered through the stimulating devices exciting the receptor cell 4) Field potentials were measured and their amplitudes were compared to determine relative strengths Rioult-Pedotti, M.S., Friedman, D., Hess, G. and Donghue, J.P. (1998). Strengthening of horizontal cortical connections following skill learning. Nature Neuroscience 1(3),

Experiment Two BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Amina  Investigated relationship between stimulus intensity and response amplitude  Clarify if rat response intensities in M1 were:  Due to skill learning OR  Due to the specific stimuli used to evoke field potentials?  Investigated relationship between stimulus intensity and response amplitude  Clarify if rat response intensities in M1 were:  Due to skill learning OR  Due to the specific stimuli used to evoke field potentials?

Experiment Two BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Amina  Method 1: Constant Fraction  Rats tested with stimuli that were a FRACTION of the maximum response intensity  Method 2: Constant Multiple  Rats tested with stimuli that were a MULTIPLE of the minimal response intensity  Method 1: Constant Fraction  Rats tested with stimuli that were a FRACTION of the maximum response intensity  Method 2: Constant Multiple  Rats tested with stimuli that were a MULTIPLE of the minimal response intensity

Experiment Two BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Amina  Logarithm of the response-amplitude ratio between groups at each stimulation intensity  Compared trained and untrained rats  Compared M1 from left and right hemispheres  WHY?  To observe differences easier  I.e. If difference = 0, ratio = 1; thus, the log ratio = 0  Logarithm of the response-amplitude ratio between groups at each stimulation intensity  Compared trained and untrained rats  Compared M1 from left and right hemispheres  WHY?  To observe differences easier  I.e. If difference = 0, ratio = 1; thus, the log ratio = 0

Results BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rory  Field potentials evoked in the trained M1 were larger in amplitude than those evoked in the untrained M1  Evoked at 60% max. stimulation intensity  Field potentials evoked in the trained M1 were larger in amplitude than those evoked in the untrained M1  Evoked at 60% max. stimulation intensity Single Case Population Average

Results BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rory Stimuli is a constant multiple of the min. stimulus intensity (12- 30µA) Stimuli is a constant multiple of the min. stimulus intensity (12- 30µA) Avrg. Response is larger for the trained M1 at every stimulus intensity Max. intensity = 220µA

Results BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rory Black circles: Log (trained M1/untrained M1) White circles: Log (left M1/right M1) Log ratio of 0 means there is no difference between the two hemispheres Black circles: Log (trained M1/untrained M1) White circles: Log (left M1/right M1) Log ratio of 0 means there is no difference between the two hemispheres Stimuli is a constant multiple of the min. stimulus intensity (12-30 µA) Max. intensity = 220µA

Results BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rory Histogram for the entire data set There is a shift towards the trained M1 Control has not shifted, neither hemisphere shows a difference Histogram for the entire data set There is a shift towards the trained M1 Control has not shifted, neither hemisphere shows a difference

Results BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rory  Clear amplitude difference between the trained and untrained M1 at evey stimulation intensity  The log difference between the hemispheres showed a shift towards the trained M1  Increased excitability of the trained M1  Is this caused by LTP?  Clear amplitude difference between the trained and untrained M1 at evey stimulation intensity  The log difference between the hemispheres showed a shift towards the trained M1  Increased excitability of the trained M1  Is this caused by LTP?

Results BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rory  Occlusion Test  If the increased postsynaptic excitability is due to LTP, further LTP will be difficult to induce  Arrows indicate LTP induction  In the control, both hemispheres were induced equally  Occlusion Test  If the increased postsynaptic excitability is due to LTP, further LTP will be difficult to induce  Arrows indicate LTP induction  In the control, both hemispheres were induced equally  But in the trained condition LTP was induced much more readily in the untrained M1  LTP of the trained M1 was occluded  Presumably because LTP has already occurred  But in the trained condition LTP was induced much more readily in the untrained M1  LTP of the trained M1 was occluded  Presumably because LTP has already occurred

Significance & Summary BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rory  This experiment demonstrated plasticity in the motor cortex following skill learning  Larger amplitude observed in the trained M1, may be due to an increase in horizontal connections between cells  Based on the occlusion test, this affect was at least partly based on LTP or LTP-like mechanism  First direct evidence that plasticity of the intracortical connections is associated with learning motor skills  This experiment demonstrated plasticity in the motor cortex following skill learning  Larger amplitude observed in the trained M1, may be due to an increase in horizontal connections between cells  Based on the occlusion test, this affect was at least partly based on LTP or LTP-like mechanism  First direct evidence that plasticity of the intracortical connections is associated with learning motor skills

References BACKGROUND AIMS OF STUDY METHODS CONCLUSIONS SIGNIFICANCE Rory Tanaka J, Horiike Y, Matsuzaki M, Miyazaki T, Ellis-Davies GCR, Kasai H Protein synthesis and neurotrophin- dependent structural plasticity of single dendritic spines. Science 310:1683–6 Rioult-Pedotti, M.S., Friedman, D., Hess, G. and Donghue, J.P. (1998). Strengthening of horizontal cortical connections following skill learning. Nature Neuroscience 1(3), Rioult-Pedotti, M.S., Friedman, D., Hess, G. and Donghue, J.P. (1994). Long-term potentiation of horizontal connections provides a mechanism to reorganize cortical motor maps. Journal of Neurophysiology 71(6),