Topic 13 - Cortical Networks. Cortical Networks - Introduction. Subcortical White Matter

Transcription

1 Topic 13 - Cortical Networks 1. Subcortical White Matter 2. Cortical networks for movement Cortical Networks - Introduction Functional regions of the brain don't work independently of one another. - Different regions work together in cortical networks. Subcortical White Matter All white matter consists of myelinated axons. Source:

2 Subcortical White Matter 3 categories of white matter fibers: 1. Projection 2. Association 3. Commissural Projection between subcortical & cortical Caudate Putamen thalamus internal capsule Almost all projection fibers travel through the internal capsule. Putamen thalamus Projection fibers in internal capsule Source: Lundy-Ekman, Neuroscience: Fundamentals for Rehabilitation, Saunders, 2002 Projection between subcortical & cortical Internal capsule regions: - Anterior limb - Genu - Posterior limb

3 Association between cortical regions within one hemisphere - Short association fibers ("U" shaped fibers) - Long association fibers Source: Lundy-Ekman, Neuroscience: Fundamentals for Rehabilitation, Saunders, 2002 Commissural between hemispheres Connect homologous areas of the cerebral hemispheres. Source: Lundy-Ekman, Neuroscience: Fundamentals for Rehabilitation, Saunders, 2002 Commissural between hemispheres Corpus Callosum, genu Corpus Callosum, body Corpus Callosum, splenium Corpus Callosum, rostrum Anterior commissure Posterior commissure

4 Topic 13 - Cortical Networks 1. Subcortical White Matter 2. Cortical networks for movement Disruption of connections between homologous areas can lead to deficits in motor control. Source: Lundy-Ekman, Neuroscience: Fundamentals for Rehabilitation, Saunders, 2002 "Alien Hand Syndrome" - Involuntary but seemingly purposeful unilateral limb movements - Sometimes observed after damage to corpus callosum and medial motor areas Corpus Callosum, body

5 Corpus Callosotomy ("split brain") 6 months poststroke: - left medial frontal lesion extending into corpus callosum right left Source: Giovannetti et al. (2005) Neuropsychologia. 43: The "Dual Premotor systems" Hypothesis: Lateral Premotor regions - externally cued movements Medial Premotor regions - internally-generated movements Alien Hand Syndrome may result from imbalance between lateral and medial premotor systems Source: Goldberg & Bloom (1990) Am. J. Phys. Med. Rehabil. 69:

6 Medial areas - internally initiated movements Lateral areas - externally cued movements Source: Kandel et al., Principles of Neural Science, McGraw Hill, 2000 (Slide from "Topic 12" lecture) "Left hand apraxia" after CC lesion - Can't pantomime object use from verbal command or visual presentation of object. Lateralization of function (ie. localization of a function to the left or right side of brain) could be a factor in production of this deficit. Evidence of Lateralization in Motor Areas e.g. M1 Left M1 Right M1 = left-handed Amount of activity (pixels) = right-handed C = contralateral (I.e. hand on opposite side of body) I = ipsilateral (I.e. hand on same side of body) Adapted from: Kim et al. (1993) Science. 261:

7 Lateralization of function in M1 - - Right M1 is mainly activated during movement of left hand - Left M1 is activated during movement of either hand (regardless of handedness) Other examples of lateralization in motor regions - - Left-brain dominance for motor planning? - Lateralization during performance of complex sequences in premotor and parietal regions? Sources: Sabate et al. (2004) Neuropsychologia. 42: ; Haaland et al. (2004) J. Cogn. Neurosci. 16: Parieto-Frontal Connections Source: Lundy-Ekman, Neuroscience: Fundamentals for Rehabilitation, Saunders, 2002

8 Importance of Parieto-Frontal Connections Premotor regions select behaviours and muscle synergies based on information supplied by posterior half of the brain this info is used by premotor regions to relate target to body position in order to act on it premotor regions also integrate cognitive information (last lecture), rules for movement Regions within the Intraparietal Sulcus (IPS) VIP = ventral intraparietal area MIP = medial intraparietal area AIP = anterior intraparietal area LIP = lateral intraparietal area Parietal lobe Adapted from: Cavada (2001) NeuroImage. 14: S21-S26. Source: Kandel et al., Principles of Neural Science, McGraw Hill, 2000

9 Anterior Intraparietal region - AIP neuron activity varies depending on object grasped. - Neurons "prefer" some shapes to others. Source: Murata et al (2000) J. Neurophysiol. 83: Anterior Intraparietal region - Some AIP neurons respond to purely visual info. Source: Murata et al (2000) J. Neurophysiol. 83: Anterior Intraparietal region - Examples of highly selective "object-type visual-dominant" AIP neurons during visual fixation of different objects. Source: Murata et al (2000) J. Neurophysiol. 83:

10 PMv might use info about size, shape and orientation of objects from AIP to choose hand shapes appropriate for a given task. Source: Kandel et al., Principles of Neural Science, McGraw Hill, 2000 Areas active in human brain during object manipulation. Anterior region of IPS PMv Source: Binkofski et al. (1999) Exp. Brain Res. 128: Human Anterior Intraparietal region also responds to pictures of "graspable" objects (hammer, house, lion, face) Source: Chao & Martin (2000) NeuroImage. 12:

11 Source: Kandel et al., Principles of Neural Science, McGraw Hill, 2000 Scott, Sergio & Kalaska (1997) J. Neurophysiol. 78: Scott, Sergio & Kalaska (1997) J. Neurophysiol. 78:

12 - MIP / area 5 provides info about how body segments are positioned (cells have "preferred postures") - PMd might use info about current posture from MIP neurons to plan movements The nervous system must also deal with higher order relationships PMd cells are active during the delay period when the rules are needed to make the appropriate movement to a given cue (discussed last lecture)

13 Biomechanical / kinetic information provided in primary motor area Complex force/emg profile Parietal (area 5) cells vs. MI cells Reflects emg/force profiles Doesn t reflect emg/force profiles Sergio, L. E. et al. J Neurophysiol 94: Summary: What part of the brain is active for a simple movement? Source: Gorbet et al. (2004) NeuroImage. 23:

14 Functional network active during a "simple" reaching movement - Medial premotor Lateral premotor M1, S1 and PPC BG thalamus "ventral stream" Adapted from: Gorbet et al. (2004) NeuroImage. 23: Take-Home Message Many regions of the brain must work together in a network to generate even "simple" motor outputs.