PMID-3411361[0] Primate motor cortex and free arm movements to visual targets in three-dimensional space. I. Relations between single cell discharge and direction of movement.
- 475/568 (83%) of cells varied in an orderly fashion with movement -- tuned to a movement direction.
- As before, binned the firing based on movement direction.
- generalize 2-D results [1][2]
- Totally awesome tracking system: a spark gap was attached to the monkey's wrist and was discharged every 20ms. The sonic signal was picked up by at least 3 of the 8 ultrasonic recievers placed at the corners of the workspace and the xyz coordinates were calculated from the sonic delays using a microprocessor-based system.
- monkey(s) had to press lighted buttons (arcade buttons) within this workspace.
- otherwise same materials / methods as before.
- every effort was made to isolate initially negative-going action potentials, and indication that the neuron was less likely to be damaged.
- fiber spikes are initially positive. Cite Mountcastle et al 1969.
- EMG signals gained 3000 and bandpassed 100-500Hz. rather narrow, but normal I guess.
- Neural data recorded as interspike intervals.
- vectoral dot-product tuning of cells, with the coeficients set by multiple linear regression.
- This is equivalent to cosine tuning.
- rather complicated CUSUM for determining onset of activity - including inhibition.
- as in the earlier study, 60% of cells were tuned in the reaction time, and 85% within the movement time.
- EMG activity looks like it can be described with cosine tuning as well.
- 3D tuning directed over the whole space.
- Residuals of firing rates measured with respect to the tuning functions; residuals were mean zero and approximately the same spread, and were distributed equally over the 3D space.
- movement latency about 300ms. pretty quick reaction time?
- Got some pretty awesome graphics for 1986 :)
- The discharge rate of motor cortical cells varies with the magnitude of force and that cells with higher thresholds are recruited at progressively higher forces (Hepp-Reymond et al 1978).
- Murphy et al 1982 found that ICMS to M1 caused rotation about single joints, which is inconsistent with cosine tuning (would require complex tuning, or tuning to joints).
- They argue that cosine tuning refects transformatino by the propriospinal system, which engages patterns of muscle activity.
- Most PTNs can influence several motoneuron pools in the spinal cord. (Fetz and Finocchio 1975, Fetz and Cheney 1978, 1980 ... Lemon 1986, Cheney and Fetz 1985)
- Suggest that PTNs related to the weighted combinations of muscles.
____References____
[0] Schwartz AB, Kettner RE, Georgopoulos AP, Primate motor cortex and free arm movements to visual targets in three-dimensional space. I. Relations between single cell discharge and direction of movement.J Neurosci 8:8, 2913-27 (1988 Aug) |
[1] Georgopoulos AP, Kalaska JF, Caminiti R, Massey JT, On the relations between the direction of two-dimensional arm movements and cell discharge in primate motor cortex.J Neurosci 2:11, 1527-37 (1982 Nov) |
[2] Thach WT, Correlation of neural discharge with pattern and force of muscular activity, joint position, and direction of intended next movement in motor cortex and cerebellum.J Neurophysiol 41:3, 654-76 (1978 May) |
|