Rachel L Spinks

Publications (4)17.73 Total impact

• Article: Modulation of primary motor cortex outputs from ventral premotor cortex during visually guided grasp in the macaque monkey.

  Gita Prabhu, Hideki Shimazu, Gabriella Cerri, Thomas Brochier, Rachel L Spinks, Marc A Maier, Roger N Lemon
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  ABSTRACT: Area F5, in the ventral premotor cortex of the macaque monkey, plays a critical role in determining the hand shape appropriate for grasp of a visible object. F5 neurones show increased firing for particular types of grasp, and inactivation of F5 produces deficits in visually guided grasp. But how is F5 activity transformed into the appropriate pattern of hand muscle activity for efficient grasp? Here we investigate the pathways that may be involved by testing the effect of single stimuli delivered through microwires chronically implanted in area F5 and in primary motor cortex (M1) of two macaque monkeys. The EMG responses from M1 test (T) stimulation were recorded from 4-11 contralateral hand, digit and arm muscles during reach-to-grasp of visually presented objects. Conditioning (C) stimulation of F5, at intensities subthreshold for motor effects, caused strong modulation (over twofold) of M1 test (T) responses. The pattern of facilitation was specific. First, facilitation of the T response was particularly evident at short C-T intervals of -1 to 1 ms. Second, this facilitation was only present in some muscles and during reach-to-grasp of a subset of objects; it did not appear to be simply related to the level of EMG activity in the muscles at the moment of cortical stimulation or indeed to the upcoming contribution of that muscle during grasp. At later C-T intervals (1-6 ms), F5 stimulation caused significant suppression of the test M1 response. The results are in keeping with the concept that during visually guided grasp, F5 modulates corticospinal outputs from M1 in a muscle- and grasp-specific manner.
  The Journal of Physiology 02/2009; 587(Pt 5):1057-69. · 4.72 Impact Factor
• Article: Selectivity for grasp in local field potential and single neuron activity recorded simultaneously from M1 and F5 in the awake macaque monkey.

  Rachel L Spinks, Alexander Kraskov, Thomas Brochier, M Alessandra Umilta, Roger N Lemon
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  ABSTRACT: The selectivity for object-specific grasp in local field potentials (LFPs) was investigated in two awake macaque monkeys trained to observe, reach out, grasp and hold one of six objects presented in a pseudorandom order. Simultaneous, multiple electrode recordings were made from the hand representations of primary motor cortex (M1) and ventral premotor cortex (area F5). LFP activity was well developed during the observation and hold periods of the task, especially in the beta-frequency range (15-30 Hz). Selectivity of LFP activity for upcoming grasp was rare in the observation period, but common during stable grasp. The majority of M1 (90 of 92) and F5 (81 of 97) sites showed selectivity for at least one frequency, which was maximal in the beta range but also present at higher frequencies (30-50 Hz). When the LFP power associated with grasp of a specific object was large in the beta-frequency range, it was usually of low power in the higher 30-50 Hz range, and vice-versa. Simple hook grips involving flexion of one or more fingers were associated with large beta power, whereas more complex grips involving the thumb (e.g., precision grip) were associated with small beta power. At many M1 sites, there was a highly significant inverse relationship between the tuning of spikes (including those of identified pyramidal tract neurons) and beta-range LFP for different grasps, whereas a positive correlation was found at higher frequencies (30-50 Hz). High levels of beta LFP and low pyramidal cell spike rate may reflect a common mechanism used to control motor set during different types of grasp.
  Journal of Neuroscience 11/2008; 28(43):10961-71. · 7.11 Impact Factor
• Article: Initial demonstration of in vivo tracing of axonal projections in the macaque brain and comparison with the human brain using diffusion tensor imaging and fast marching tractography.

  Geoffrey J M Parker, Klaas E Stephan, Gareth J Barker, James B Rowe, David G MacManus, Claudia A M Wheeler-Kingshott, Olga Ciccarelli, Richard E Passingham, Rachel L Spinks, Roger N Lemon, Robert Turner
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  ABSTRACT: Diffusion tensor imaging (DTI), a magnetic resonance imaging technique, is used to infer major axonal projections in the macaque and human brain. This study investigates the feasibility of using known macaque anatomical connectivity as a "gold-standard" for the evaluation of DTI tractography methods. Connectivity information is determined from the DTI data using fast marching tractography (FMT), a novel tract-tracing (tractography) method. We show for the first time that it is possible to determine, in an entirely noninvasive manner, anatomical connection pathways and maps of an anatomical connectivity metric in the macaque brain using a standard clinical scanner and that these pathways are consistent with known anatomy. Analogous human anatomical connectivity is also presented for the first time using the FMT method, and the results are compared. The current limitations of the methodology and possibilities available for further studies are discussed.
  NeuroImage 05/2002; 15(4):797-809. · 5.89 Impact Factor
• Source

  Available from: Geoffrey J M Parker

  Article: Initial Demonstration of in Vivo Tracing of Axonal Projections in the Macaque Brain and Comparison with the Human Brain Using Diffusion Tensor Imaging and Fast Marching Tractography

  Geoffrey J.M. Parker, Klaas E. Stephan, Gareth J. Barker, James B. Rowe, David G. MacManus, Claudia A.M. Wheeler-Kingshott, Olga Ciccarelli, Richard E. Passingham, Rachel L. Spinks, Roger N. Lemon, Robert Turner
  [show abstract] [hide abstract]
  ABSTRACT: Diffusion tensor imaging (DTI), a magnetic resonance imaging technique, is used to infer major axonal projections in the macaque and human brain. This study investigates the feasibility of using known macaque anatomical connectivity as a “gold-standard” for the evaluation of DTI tractography methods. Connectivity information is determined from the DTI data using fast marching tractography (FMT), a novel tract-tracing (tractography) method. We show for the first time that it is possible to determine, in an entirely noninvasive manner, anatomical connection pathways and maps of an anatomical connectivity metric in the macaque brain using a standard clinical scanner and that these pathways are consistent with known anatomy. Analogous human anatomical connectivity is also presented for the first time using the FMT method, and the results are compared. The current limitations of the methodology and possibilities available for further studies are discussed.
  NeuroImage.