Tool responsive regions in the posterior parietal cortex: effect of differences in motor goal and target object during imagined transitive movements.

Abstract

Neuroanatomical and functional studies have proposed a functional segregation of the human dorsal stream into a dorso-dorsal pathway, believed to serve as an object-independent stream involved with on-line control of action, and a ventro-dorsal pathway that provides conceptual input guiding the functional manipulation of objects. We aim to evaluate whether the inferior parietal cortex deals specifically with action reliant on stored knowledge. Fifteen right-handed, normal volunteers varied the intention of their transitive movements by imagining their dominant arm and hand pointing to, grasping to move, grasping to use, or grasping and using three-dimensional representations of target objects depicting graspable neutral shapes, unfamiliar tools, and familiar tools. Imagined movements intended to make functional use of familiar objects revealed increased activation in the left inferior parietal lobule. Compared to gestures aimed at displacing an object, functional (use) intentions elicited activation in the anterior and middle portions of the lateral bank of the intraparietal sulcus, suggesting involvement in the higher order control of action. Compared to functionally unfamiliar objects, grasping movements aimed at familiar tools activated the convex portion of the inferior parietal lobule, suggesting a role for the ventro-dorsal stream in object-selectivity. These data confirm that stored knowledge for the skillful manipulation of familiar tools of right-handed volunteers is predominantly located in the left inferior parietal lobule, and further suggest that tool use-responsive regions and tool object-responsive regions are not identical, but may form a local network in which different nodes contribute differently to the representation of functional tool use in humans.

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Tool responsive regions in the posterior parietal cortex: Effect of differences
in motor goal and target object during imagined transitive movements
Guy Vingerhoets, Frederic Acke, Pieter Vandemaele, Eric Achten
PII:
DOI:
Reference:
S1053-8119(09)00615-6
doi:10.1016/j.neuroimage.2009.05.100
YNIMG 6327
To appear in:
NeuroImage
Received date:
Revised date:
Accepted date:
23 December 2008
29 May 2009
30 May 2009
Please cite this article as: Vingerhoets, Guy, Acke, Frederic, Vandemaele, Pieter, Achten,
Eric, Tool responsive regions in the posterior parietal cortex: Effect of differences in
motor goal and target object during imagined transitive movements, NeuroImage (2009),
doi:10.1016/j.neuroimage.2009.05.100
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Tool responsive regions in the posterior parietal cortex: Effect of differences in
motor goal and target object during imagined transitive movements
Guy Vingerhoets 1,2, Frederic Acke 1,2, Pieter Vandemaele 2,3, Eric Achten 2,3
(1) Laboratory for Neuropsychology, Department of Neurology, Ghent University
(2) Ghent Institute for Functional and Metabolic Imaging, Ghent University
(3) Department of Radiology, Ghent University
Corresponding author: Guy Vingerhoets
De Pintelaan 185 4K3, B-9000 Ghent, Belgium
Tel.: +32-9-240 45 87
Fax: +32-9-240 45 55
E-mail: guy.vingerhoets@ugent.be
Running title: Imagined transitive movements
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Abstract
Neuroanatomical and functional studies have proposed a functional segregation of the
human dorsal stream into a dorso-dorsal pathway, believed to serve as an object-
independent stream involved with on-line control of action, and a ventro-dorsal
pathway that provides conceptual input guiding the functional manipulation of
objects. We aim to evaluate whether the inferior parietal cortex deals specifically with
action reliant on stored knowledge. Fifteen right-handed, normal volunteers varied the
intention of their transitive movements by imagining their dominant arm and hand
pointing to, grasping to move, grasping to use, or grasping and using three-
dimensional representations of target objects depicting graspable neutral shapes,
unfamiliar tools, and familiar tools. Imagined movements intended to make
functional use of familiar objects revealed increased activation in the left inferior
parietal lobule. Compared to gestures aimed at displacing an object, functional (use)
intentions elicited activation in the anterior and middle portions of the lateral bank of
the intraparietal sulcus, suggesting involvement in the higher order control of action.
Compared to functionally unfamiliar objects, grasping movements aimed at familiar
tools activated the convex portion of the inferior parietal lobule, suggesting a role for
the ventro-dorsal stream in object-selectivity. These data confirm that stored
knowledge for the skillful manipulation of familiar tools of right-handed volunteers is
predominantly located in the left inferior parietal lobule, and further suggest that tool
use-responsive regions and tool object-responsive regions are not identical, but may
form a local network in which different nodes contribute differently to the
representation of functional tool use in humans.
Key words: fMRI, human, parietal cortex, praxis, tool use
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Neuroanatomical and functional studies have proposed a further distinction of the
dorsal visual system (Rizzolatti and Matelli, 2003; Tanne-Gariepy et al., 2002). In the
monkey brain, a dorso-dorsal stream originates from an extrastriate visual node V6,
and connects with areas V6A and MIP (medial intraparietal area) of the superior
parietal lobule (SPL), which is closely linked with the proprioceptive somatosensory
system. The SPL is further connected to the dorsal premotor cortex (F2) (Rizzolatti
and Luppino, 2001). Its major functional role is described as important for the ‘on
line’ control of action. A ventro-dorsal stream stems from another extrastriate node
MT (middle temporal), and connects to the inferior parietal lobule (IPL) and medial
superior temporal area (MST). IPL projects to the ventral premotor cortex (F4, F5)
and prefrontal cortex. In addition to action organization, the ventro-dorsal stream is
hypothesized to play role in object awareness, control of hand posture, and action
understanding (Rizzolatti and Matelli, 2003). Based on neuropsychological evidence
and functional imaging data, it is suggested that a comparable segregation might exist
in humans, one for acting on and another for acting with objects, and that hand-object
interactions follow different streams dependent on the goal to be achieved (Buxbaum
et al., 2006; Buxbaum et al., 2007; Daprati and Sirigu, 2006; Johnson and Grafton,
2003; Johnson-Frey, 2004). If an object is to be moved (acting on), visual information
regarding the object’s intrinsic (shape and size) and extrinsic (orientation and
location) qualities will guide the movement’s reach trajectory and grasp aperture.
Conceptual knowledge about the target is not required and the movement is guided by
a more superior parietal network. Damage to (or interruption of) this pathway results
in optic ataxia, a deficit in motor control characterized by poor and awkward reach
trajectories and grasping of neutral objects in the peripheral visual fields (Karnath and
Perenin, 2005). If we wish to use the object (acting with), stored knowledge about its
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functional properties becomes relevant and is integrated with the perceptual
affordances of the ‘on-line’ pathway. This conceptual input probably relies on
structures in the inferior parietal cortex and guides a ‘functional’ grasp and eventual
purposeful movement with the object. Obviously this behavior can only be performed
with familiar objects whose function we know. Damage to this pathway is illustrated
by a form of apraxia showing adequate target grasping but impaired functional
grasping when aiming to use the object (Sirigu et al., 1995).
This fMRI study tests the assumption that increased functional relevance of
movement or target preferentially activates inferior parietal regions by presenting
normal volunteers with three-dimensional representations of different sets of objects
(neutral shapes, unfamiliar tools, and familiar tools) and asking them to perform
different movements toward them: point (baseline), grasp with the intention to move
the object (mechanical grasp), grasp with the intention to use the object (functional
grasp), and use the object (functional grasp + functional movement). A schematic
overview of the conditions is depicted in Figure 1A. Given the physical constraints of
the scanner environment and the susceptibility of fMRI to movement artifacts, we
asked our participants to imagine the movements instead of actually performing them.
There is ample evidence that in healthy volunteers, motor imagery, the covert
simulation of movement, involves much of the same neural correlates as the overt
behavior, although there are differences (Binkofski et al., 2000; Gerardin et al., 2000;
Hanakawa et al., 2003; Lotze et al., 1999). The major drawback of mental imagery is
that there is no overt movement and correct performance of the task is difficult to
control. We used the established close temporal coupling between motor imagery and
executed movement to ascertain adequate performance by our participants (Decety et
al., 1989).
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Based on the above assumptions, several hypotheses can be tested. With
regard to the goal of the movement, we expect an increasing involvement of inferior
parietal lobule activation with an increasing demand of functionally relevant
‘knowledge’ (grasp to move < grasp to use < use). With regard to the target object, we
expect an increasing involvement of the inferior parietal lobule with an increasingly
functional ‘appearance’ of the object during a similar task (neutral shape < unfamiliar
tool < familiar tool).
Materials and methods
Stimuli
The sets of familiar and unfamiliar tools used in this study were identical in type to
those used in an earlier fMRI study on tool knowledge, in which the realization of the
tool collection and the rationale for selection were extensively described
(Vingerhoets, 2008). In short, a normative group of fifty normal volunteers (25 of
each gender, Mean (M) age 44.1 years, Standard Deviation (SD)17.8 years) rated a
collection of 142 common and unusual tools for graspability, knowledge of function,
and hands-on experience. Based on these ratings, we selected thirty tools that were
rated low on functional knowledge and received low experience ratings, yet were
considered highly graspable, to compile a set of ‘unfamiliar’ tools. In fact, functional
knowledge ratings of the unfamiliar tools showed that participants had little, if any,
understanding of the functional purpose of these tools. A second set of thirty highly
graspable tools that rated high on functional knowledge and received high experience
ratings was selected to make up a set of ‘familiar’ tools. As a result, while there was
no significant difference in the graspability ratings of the two sets, functional
knowledge and experience ratings differed significantly, with higher scores for the
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familiar tools (always p<.001). In addition to these two sets, we collected 30 simple
and highly graspable geometric shapes (cylinder, cone) made from metal, wood or
polystyrene foam that were at least three times longer than they were wide. A Canon
EOS 300D reflex camera mounted on a Photo3D Model 303 adapter (Mission3D,
LLC, Exeter, USA) was used to capture a left-eye and right-eye image (stereo pair) of
each tool and shape. The aim of the three dimensional presentation of the target
objects through stereoscopic goggles was to enhance the ecological validity of the
task and to aid the participants in motor imagery. Picture-editing software (Adobe
Photoshop) was used to construct two pictures of each stereo pair on a uniform gray
background, oriented so as to be compatible with right-hand grip in one case and left-
hand grip in the other. Finally, Photo3D mixer software was used to merge and focus
the left and right-eye images. Hundred-and-eighty stimuli were thus created
consisting of 60 stereo pairs of unfamiliar tools (30 oriented to the right hand and 30
to the left) and 60 stereo pairs of familiar tools (30 to the right and 30 to the left), and
60 stereo pairs of neutral shapes (30 to the right and 30 to the left). Some examples of
these stimuli are depicted in Figure 1A and a list of the familiar tools can be found in
the Appendix.
Participants
Fifteen healthy volunteers participated in the study (range: 19-24 years, mean age: 21,
7 women and 8 men). All were right handed as determined by the Edinburgh
Handedness Inventory: M = 88.3%, SD = 18.6% (Oldfield, 1971). None had a history
of neurological or psychiatric disease. Scanning protocols were approved by the local
ethics committee and all subjects gave written informed consent after the
experimental procedure was explained.
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Procedure
Prior to scanning, the volunteers completed a pre-scan MRI-safety questionnaire and
the Edinburgh Handedness Inventory. They were instructed that before each set of 6
targets they would see a written instruction of what movement they were supposed to
imagine with the target object. There were four types of instructions. The first
instruction ‘Point’ served as a baseline condition because it can be performed toward
any object and, like grasping, requires a similar object-related reaching movement and
yet, unlike grasping, requires merely a stereotypical hand posture and no interaction
with the object. The ‘Point’ instruction indicated that upon the appearance of the first
object they were to imagine lifting their dominant (right) hand off their chest,
reaching toward the 3D object and pointing to it with a stretched index finger, and to
keep on looking at the object until the next stimulus appeared. They were also
instructed to press the right key of an MRI-compatible two-button response device
(Lumina LP-400, Cedrus Corporation, San Pedro, CA, USA) with the index finger of
their left hand if the pointing movement was finished and the tool almost touched.
The non-dominant method of response (i.e. left hand only) was specifically chosen to
avoid any interference between this response and the generation of the imagined
motor response with the dominant hand during the observation of the stimuli.
Following the second instruction, ‘Grasp to move’, the volunteers had to imagine
lifting the dominant hand, reaching toward the object and grasping it in order to move
it about 1 decimeter, and then putting it back down. They were also instructed to press
the button with the left hand the moment their fingers first ‘touched’ the object. After
the third instruction, ‘Grasp to use’, they had to imagine lifting the hand and making a
reaching movement toward the object, then grasping the object as if they were going
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to use it for its appropriate function, and to maintain that grasp until the next stimulus
appeared. When performing this task with an unfamiliar tool, they were required to
perform the most plausible grasp in order to use the object. All unfamiliar tools were
highly graspable and had an obvious functional part and a clear handle or grip part,
leaving little doubt as to the functional grasp of the tool. Again, they were instructed
to press the button with the left hand the moment their fingers first ‘touched’ the
object. The fourth instruction, ‘Grasp and use’, indicated that they were to imagine
lifting the right hand from the chest, making a reaching movement toward the 3D
object, grasping the object in order to use it, and making three functionally
appropriate unimanual movements with it. Here too, they were instructed to give a
button press with the left hand the moment their fingers first ‘touched’ the object.
Meaningful combinations of commands and objects resulted in the nine conditions
summarized in Figure 1A. By manipulating the orientation of the object/tool and by
asking the volunteers to press a (left hand) button upon imagined first touch of the
object, we aim to demonstrate that non-canonical orientations for a right hand grasp
took the participants significantly longer to imagine, suggesting an adequate use of
motor imagery. The participants were asked to imagine making the movements slowly
rather than quickly, and as vividly as possible, trying to ‘feel’ their arm and hand
movements during the reaching and grasping movements and to ‘see’ how their hand
grasped and manipulated the object. In order to stretch the movement over the entire
stimulus presentation, we did not specify a physically plausible end of the movement.
This might have resulted in an interruption of the imagery process or a hurried
(imagined) withdrawal of the hand at the beginning of every following trial, but this
effect would be similar to each condition. Some examples were provided so that they
could get used to the pace at which the stimuli were presented and to ascertain that
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they all correctly understood the instructions and were able to perform the task. The
aim of the study was not explained until the scanning was completed.
The volunteers were positioned head first and supine in the magnet. The right
arm was bent with the right hand resting loosely on the chest; the left arm was
positioned alongside the body with the left index finger stretched over the button
press that was held in the left hand. Stimuli were presented through goggles with an
MRI-compatible presentation system (VisuaStim-Digital, Resonance Technology
Inc., California, USA). Participants were instructed to lie as still as possible to prevent
motion artifacts and to restrict head movements. Their heads were gently fixed in
place with foam cushions.
Stimulus presentation and response recording was controlled by a
commercially available experiment generator (Presentation, Neurobehavioral Systems
Inc., Albany CA, USA). The paradigm was arranged as a conventional block design
with nine conditions. Each condition consisted of 8 blocks containing stimuli of
familiar tools, unfamiliar tools, or non-objects. A block lasted 32s and consisted of a
fixation cross (2s), an instruction screen indicating the task to be performed (3s), and
six stimuli each presented for 4.5s, regardless of the behavioral response. The total
experiment thus took 38.4 minutes, and was divided into four runs of 9.6 minutes
each. Each run consisted of 18 blocks, two of each condition, that were ordered semi
randomly to avoid consecutive presentation of two blocks with the same type of
stimuli. Each of the 90 stimuli was available in two orientations, once compatible
with a right hand grasp and once compatible with a left hand grasp. Stimuli were
randomly distributed over their conditions’ blocks. Between each run, volunteers were
allowed a short break and the next run was not started without their permission.
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In the post-scan session, participants completed a post-scan MRI safety
questionnaire. They were then presented with pictures of the familiar and unfamiliar
tools they had seen during the paradigms and instructed to rate each on a five-point-
scale for graspability, knowledge of its function, and hands-on experience. These
data allowed us to compare the volunteers’ ratings against those of the normative
group originally used to select the tools. The neutral shapes were rated on graspability
only. Finally, the volunteers were asked to complete the revised Movement Imagery
Questionnaire (MIQ,(Hall and Martin, 1997)). The MIQ assesses individual
differences in visual and kinesthetic movement imagery abilities and has been shown
to predict the use of imagery in athletes (Rodgers et al., 1991). This self-report
measure was used to compare the participants’ subjective impressions of their motor
imagery abilities against normative data (Hall and Martin, 1997).
Scanning procedure
Scanning was performed at 3.0 T on a Siemens Trio MRI scanner (Siemens Medical
Systems, Erlangen, Germany) equipped with echo planar imaging (EPI) capabilities
using an eight-channel PA head coil for radio frequency transmission and signal
reception. After automatic shimming of the magnetic field on each participant, a 3D
high-resolution T1 anatomical image of the whole brain in the sagittal plane was
acquired (3D MPRAGE, 176 slices, slice thickness = 0.9, in-plane resolution = 0.9 x
0.9 mm, TR = 2530 ms, TE = 2.58) for coregistration with the functional images.
Next, 928 functional EPI images in the axial plane were acquired for the entire
paradigm (232 during each run). They had the following parameters: TR = 2.5 s, TE =
33 ms; flip angle = 90°, 33 slices, slice thickness = 2.5 mm, slice gap = 1.25 mm,
FOV = 192 mm and matrix = 64 x 64, resulting in a resolution of 3 x 3 x 2.5 mm.
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Image analysis
Data analysis was performed using Brain Voyager QX for preprocessing and
statistical inference (Goebel et al., 2006). The functional data set acquired from each
run consisted of 232 image volumes. Functional data were subjected to a standard
sequence of preprocessing steps comprising slice scan time correction using sinc
interpolation, 3-D motion correction by spatial alignment to the first volume also
using sinc interpolation, and temporal filtering using linear trend removal and high
pass filtering for low-frequency drifts of 3 or fewer cycles. Spatial smoothing using a
Gaussian filter (FWHM = 8 mm) was applied for the volume based analysis. The
anatomical data for each subject were resampled to 1-mm resolution, and transformed
into Talairach standard space using sinc interpolation. The functional data for each
subject were coregistered with the subject's 3-D anatomical dataset and transformed
into Talairach space.
From each run of each subject's paradigm, a protocol file representing the
onset and duration of each block for the different conditions was derived. Factorial
design matrices were defined automatically from the created protocols. The BOLD
response in each condition was modeled by convolving these neural function with a
canonical hemodynamic response function (gamma) to form covariates in a General
Linear Model (GLM). After the GLM had been fitted and the effects of temporal
serial correlation allowed for (using AR(1) modeling; (Bullmore et al., 1996)), group
(random effects procedure) t-maps were generated to evaluate the effects of imagining
transitive movements, of intention of the movement, and of target of movement
(object quality). The specific contrasts performed are detailed in the respective parts
of the results section below. First, we analyzed the data set using a whole-volume
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voxel-wize approach to reveal the BOLD response in the entire cerebrum under the
different conditions. Later, more specific contrasts were performed over a priori
determined regions of interest (ROI) in order to increase statistical power. Since all of
our hypotheses pertain to the posterior parietal cortex, we focus our analysis on these
regions only. The a priori defined anatomical ROIs were drawn on a group-averaged
3D anatomical image of the scanned group and the posterior parietal ROI's were
separately determined for each hemisphere, with the brain atlases of Duvernoy and
Talairach & Tournoux being used for reference (Duvernoy, 1991; Talairach and
Tournoux, 1988). The posterior parietal ROIs included the superior and inferior
parietal lobules, and the precuneus (most anterior y = -20, most posterior y = -77,
most cranial z = 75, most caudal z = 22). The anatomical ROIs were converted into
volumes-of-interest that were used as masks in conventional GLM-analyses.
Although most neuroimaging studies on tool use applied uncorrected thresholds of
p<.001, this study uses a threshold of p < .05 corrected for multiple comparisons
using False Rate Discovery (FDR) correction (Genovese et al., 2002). As some
conditions differ more or differ less from others, contrasts will lead to activation
patterns of diverse strength. Most contrasts in this study can be adequately described
with the p<.05 FDR-corrected threshold, but in some cases this threshold required
adaptation (strengthening as well as weakening) to be able to describe both robust and
subtle differences. If statistical thresholds were adapted, this is always made explicit
in the text, table, or figure.
Results
Behavioral data
Tool ratings
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The scanned volunteers considered the unfamiliar tools just as graspable as familiar
tools (M = 4.47 (SD = .38) versus 4.48 (SD = .40) respectively, no significant
difference), but (as expected) rated them significantly lower on functional knowledge
(M = 1.50 (SD = .32) versus 4.46 (SD = .35), p<0.001) and hands-on experience (M =
1.12 (SD = .14) versus 3.87 (SD = .43), p<0.001). Neutral shapes were rated
somewhat less graspable than tools (M = 4.26 (SD = .52), a significant difference
compared to familiar tools (p = 0.028) and close to significance compared to
unfamiliar tools (p = 0.053). No significant differences in tool ratings were found
between the scanned participants and the normative sample, with the exception that
the former rated the familiar tools somewhat lower on functional knowledge than the
latter (M = 4.46 (SD = .35) versus 4.73 (SD = .27), p=0.003). The low standard
deviations of both functional knowledge and hands-on experience ratings reflect the
high level of consensus between participants regarding their score on these
dimensions. Closer inspection of the ratings showed that this was the case for each
and every tool, and that no one individual stood out regarding tool knowledge or
experience.
Imagery performance
The participants’ mean sum scores on the revised Movement Imagery Questionnaire
for the kinesthetic and visual subscales measured 18.67 (SD = 5.0) and 24.20 (SD =
4.7) respectively. These scores are very similar to the normative data provided in the
literature (Hall and Martin, 1997) (18.66 and 24.58 respectively, n = 50), as was the
finding that visual imagery ability is generally better than kinesthetic imagery ability
(t(14) = -3.12, p = 0.007). On a scale of 1 (very hard to see/feel) to 7 (very easy to
see/feel), participants’ mean single visual subscale score was 6.05 (SD = 1.14) (= easy
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to see) and their mean single kinesthetic subscale score was 4.67 (SD = 1.26) (=
between somewhat easy to feel and neutral = neither easy nor hard to feel)). Low
standard deviations suggest little variability for these subjective ratings between
subjects.
Mean time-to-touch values were calculated for each participant within each
experimental condition. RTs greater than 4500 ms (time outs) or less than 500 ms
(anticipations) were removed from the data set. These exclusions represented 0.76%
of all trials.
The mean time-to-touch values were submitted to a repeated measures
analysis of variance with 2 (orientation: canonical or non-canonical orientation) × 9
(conditions) as within-subjects factors (Figure 2). The analysis showed a significant
main effect of orientation, such that responses toward non-canonically oriented
objects were slowest (M=2228 ms, SD=622) and those toward canonically oriented
objects were fastest (M=2166 ms, SD=615), F(1, 14) =13.65; p = .002. A significant
main effect for condition was also obtained, such that shapes in general elicited faster
responses than tools and that the imagining of moving objects elicited faster responses
than that of pointing, grasping, or using, F(8,7)=4.95, p=.024. We found no
significant orientation by condition interaction effect, F(8,7)=2.66, p=.11.
Imaging data
Imaging transitive movements
To evaluate cerebral activation elicited by imagined transitive movements as opposed
to imagined pointing, we compare imagined use, functional grasping, and mechanical
grasping of familiar tools with imagined pointing to the same objects (random effects
alpha(FDR) < 0.005, whole brain analysis). As illustrated in Figure 1B, imagining
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