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ref: RodriguezOroz-2001.09 tags: STN SNr parkinsons disease single unit recording spain 2001 tremor oscillations DBS somatotopy organization date: 02-22-2012 18:24 gmt revision:12 [11] [10] [9] [8] [7] [6] [head]

PMID-11522580[0] The subthalamic nucleus in Parkinson's disease: somatotopic organization and physiological characteristics

  • Looks like they discovered exactly what we have discovered ... only in 2001. This is both good and bad.
    • From the abstract: "Neurones responding to movement were of the irregular or tonic type, and were found in the dorsolateral region of the STN. Neurones with oscillatory and low frequency activity did not respond to movement and were in the ventral one-third of the nucleus. Thirty-eight tremor-related neurones were recorded."
  • Again, from the abstract: "The findings of this study indicate that the somatotopic arrangement and electrophysiological features of the STN in Parkinson's disease patients are similar to those found in monkeys."
  • It may be that we want to test differential modulation / oscillation: look for differences between rest and activity, if there is sufficient support for both these in the files we have.
  • These people were much, much more careful about localization of their single-electrode tracks. E.g. they calculated electrode location relative the DBS electrode stereotatically, and referenced this to the postoperative MRI location of the treatment electrode.
  • Many more (32% of 350 neurons) responded to active or passive movement.
  • Of this same set, 15% (31 neurons) had a firing rate with rhythmical activity; 38 neurons had rhythmic activity associated with oscillatory EMG, but most of these were responsive to passive stimulation.
  • Autocorrelation of the neuronal bursting and tremor peaked at mean 7Hz, while autocorr. of EMG peaked at mean 5Hz.
  • This whole paragraph is highly interesting: ''The neuronal response associated with active movements was studied by simultaneous recording of neuronal EMG activity of the limbs. Five tremor-related neurons, recorded while a voluntary movement was performed, were available for analysis. Voluntary activation of a particular limb segment arrested the tremor. This was associated with a change in the discharges of the recorded neuron, which fired at a slower rate and in synchrony with the voluntary movement. On occasions, freezing of the voluntary movement ensued and tremor reappeared, changing the neuronal activity back to the typical 4-5Hz tremor-related activity. The cross-correlation analysis of two such neurons showed a peak frequency of 4.63 and 4.88 Hz for tremor-related activity, and 1.5 to 1.38 Hz during voluntary movement. Whether neuronal discharges in the STN preceded or followed EMG activity of the limbs could not be precisely established under the present conditions.
  • Somatotopic representation in the STN is expected from normal and MTPT-treated monkeys. Indeed, somatotopy is enhanced int he GPm of MTPT-treated monkeys.
    • This somatotopy is likely to result from organized afferent from the primary motor cortex (M1) to dorsolateral STN; this is the target of DBS treatment. Ventral and medial STN seems to project to associative and limbic cortical regions.
    • It seems they think the STN is generally not diseased, it is just a useful target for stimulating without evoked movement as in M1. This is consistent with optogenetic studies by Deisseroth [1].
    • Supporting this: "DBS of STN in Parkinson's disease improves executive motor functions, but aggravates conditional associative learning.
  • Interesting: In Parkinson's disease patients with tremor, Levy and colleagues found synchronization and a high firing rate (>10Hz) while recording pairs of neurons >600um apart.
  • Recordings of cortical activity through EEG and STN LFP showed significant coherence in the beta and gamma frequency bands during movement - consistent with corticosubthalamic motor projection. ... and suggest that the STN neurons involved in parkinsonian tremor are the same as the ones ativated during the performance of a voluntary movement. (! -- I agree with this.)
  • More: The reciprocal inhibitory-excitatory connections tightly linking the GPe and the STN may generate self-perpetuating oscillations.

Old notes:

  • this paper concentrates on STN electrophysiology in PD.
    • has a rather excellent list of references.
  • found a somatotopic organization in the STN, with most motor-related units more irregular and in the dorsolateral STN.
  • found a substantial fraction of tremor-synchronized neurons.
  • conclude that the somatotopic organization is about the same as in monkeys (?) (!)
  • M1 projects to STN, as verified through anterograde tracing studies. [1] These neurons increase their firing rate in response to passive movements.
  • there appears to be a relatively-complete representation of the body in the dorsolateral STN.

____References____

[0] Rodriguez-Oroz MC, Rodriguez M, Guridi J, Mewes K, Chockkman V, Vitek J, DeLong MR, Obeso JA, The subthalamic nucleus in Parkinson's disease: somatotopic organization and physiological characteristics.Brain 124:Pt 9, 1777-90 (2001 Sep)
[1] Gradinaru V, Mogri M, Thompson KR, Henderson JM, Deisseroth K, Optical deconstruction of parkinsonian neural circuitry.Science 324:5925, 354-9 (2009 Apr 17)