DOES IT EXIST A LINK BETWEEN PERFORMANCE

AND PARIETAL CORTEX ACTIVITY IN SURGICAL TASKS?

G. Paggetti, Y.-C. Lin, G. Menegaz

Department of Computer Science, University of Verona, Verona, Italy

D. R. Leff, G.-Z. Yang

Biosurgery and Surgical Technology, Imperial College London, London, U.K.

Keywords:

Functional near infrared spectroscopy (fNIRS), Depth perception, Hand-eye coordination, da Vinci surgical

system, Posterior parietal cortex.

Abstract:

This pilot study would to explore the ideas of a possible correlation between the goodness of surgical per-

formance in robotic assisted minimally invasive surgery (MIS) and posterior parietal cortex (PPC) activity.

This cortical area is known to be involved in stereoscopic vision (Sakata et al., 1997), visual control of eye

movements and hand-eye co-ordination (Shikata et al., 1996). This issue is of great interest because robotic

assisted surgery provides the surgeon with a stereoscopic view of the operative ﬁeld combined with aligned

motor-visual axes and mechatronically controlled instruments. In this contribution, we conduct an exploratory

experiment aiming at investigating the hypothesis of a correlation between the performance in reached in a

surgically relevant task and the activation of PPC channels as revealed by the fNIRS measurements. First

results are very promising and suggest the occurrence of a link between performance and channel activation.

1 INTRODUCTION

The posterior parietal cortex (PPC) is known to be

involved in stereoscopic vision (Sakata et al., 1997;

Shikata et al., 1996), visual control of eye move-

ments and hand-eye co-ordination (Ferraina et al.,

2009; Kim and James, 2010). This brain region may

play an important role in robotic assisted interven-

tion which provides the surgeon with a stereoscopic

view of the operative ﬁeld combined with aligned

motor-visual axes and mechatronically controlled in-

struments. Theoretically, performers with superior

technical ability may demonstrate enhanced neuronal

efﬁciency compared to those who struggle in robotic

environments. This pilot study explores the link be-

tween technical ability and PPC activation during

depth perception and a hand-eye coordination task in

a robotic surgical environment. The PPC activation

was investigate both by a group analysis and by a

subject by subject analysis. Early results are promis-

ing and may suggest a link between technical perfor-

mance and PPC excitation.

2 MATERIALS AND METHODS

Four, right-handed, healthy subjects participated in

this study. Optical topography (OT) assessment was

conducted for two experiments involving monoscopic

and stereoscopic object depth perception and hand-

eye coordination tasks in a robotic surgical environ-

ment. The experiment was conducted using the da

Vinci Surgical System (Intuitive Surgical, Inc., USA).

In the ﬁrst experiment (object depth perception) sub-

jects were shown a platform of nine numbered spheres

of random size, positioned at different depths and

were asked to vocally indicate the nearest and far-

thest sphere. In the second experiment (hand-eye-

coordination) subjects were required to manipulate

the robotic arms to move elastic bands between pre-

deﬁned locations (cones) in the operative ﬁeld. Both

experiments were conducted using a block design

paradigm consisting of self paced stimuli and inter-

trial visuomotor rest (30s). Five blocks of trials were

performed using 2D visual stimulus rendering and

ﬁve using 3D. In each condition, randomization was

used to eliminate ordering effects. PPC activity was

indexed by changes in cortical haemodynamics mea-

381

Paggetti G., Lin Y., Menegaz G., R. Leff D. and Yang G..

DOES IT EXIST A LINK BETWEEN PERFORMANCE AND PARIETAL CORTEX ACTIVITY IN SURGICAL TASKS?.

DOI: 10.5220/0003114003810384

In Proceedings of the International Conference on Fuzzy Computation and 2nd International Conference on Neural Computation (ICNC-2010), pages

381-384

ISBN: 978-989-8425-32-4

 2010 SCITEPRESS (Science and Technology Publications, Lda.)

Figure 1: Illustration of the patterns of task-evoked changes in oxyhaemoglobin (HbO

), and deoxyhaemoglobin (HHb)

across depth perception (A) and hand-eye coordination (B) trials. HbO

increment and HHb decrement indicating activations

(red circles). HbO

decrement and HHb increment indicating deactivations (blue circles). Both Hb species increasing or

decreasing (yellow circles).

ured using Functional Near Infrared Spectroscopy

(fNIRS) based OT equipment (ETG-4000, Hitachi

Medical Corp, Japan). OT enables repeated non-

invasive assessments of oxygenated haemoglobin

(HbO

) and deoxygenated haemoglobin (HHb) in-

ferring brain function (increase in HbO

coupled to

decrease in HHb) during complex tasks in realistic

environments (Leff et al., 2008). This system was

used to acquire functional haemodynamic data from

24 locations (channels) across bilateral posterior pari-

etal lobes simultaneously. All trials were videotaped

to enable performance analysis. Performance in the

object depth perception experiment was assessed as

the percentage of correct depth identiﬁcation for each

sphere-set (%). Blinded error ratings by two inde-

pendent observers against operation speciﬁc check-

lists resulted in objective scores of technical skill in

the hand-eye coordination experiment. For each chan-

nel, haemodynamic data were block averaged. Then,

mean change (increase/ decrease) from baseline rest

in HbO

and HHb was calculated on a subject by sub-

ject basis. Changes in oxyhaemoglobin (HbO

), and

deoxyhaemoglobin (HHb) from rest were statistically

analysed using Wilcoxon Sign Rank Test (p<0.05) to

determine the location of activated channels (stimu-

lus evoked increase in HbO

coupled to a decrease in

HHb) in the group analysis. Additionally, the magni-

tude of ∆Hb values (Hb Stimulation Hb Rest) were

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382

Figure 2: Illustration of subject performance during depth perception (A) and hand-eye coordination tasks (B).

compared between 2D and 3D trials for each channel

to determine whether parietal activation was signiﬁ-

cantly greater during 3D trials versus 2D (Wilcoxon

Sign Rank Test, p<0.05). .

3 RESULTS

3.1 Group Analysis

Depth perception accuracy was signiﬁcantly better

during 3D versus 2D performance (% of spheres cor-

rectly identiﬁed). Hand eye-coordination was signiﬁ-

cantly better during 3D performance, with more tech-

nical errors being committed in 2D. The location of

activated channels was observed to be function of task

domain. Right PPC recruitment was required during

object depth perception without movement and dur-

ing visually guided manipulation of the robotic arms.

In contrast, left PPC activation occurred only during

the hand-eye coordination task and was not recruited

during object depth perception alone. The difference

in functional brain responses between 2D and 3D tri-

als was not manifested by a variation in the location

of activated channels but instead by the magnitude

of parietal excitation. The magnitude of ∆HbO

and

∆HHb was found to be greater during 3D versus 2D

trials in many parietal channels, for both experiments.

3.2 Subject by Subject Analysis

The results suggest that a link may exist between tech-

nical performance, depth perception capability and

PPC activation. As illustrated in Figures 1 and 2, Sub-

jects (e.g. Subj01) with poorer technical and depth

perception capability and appear to activate the bilat-

eral PPC more broadly than subjects (e.g. Subj02)

with superior visuospatial ability and technical skill.

Moreover, subjects reaching an intermediate level

of performance in both tasks demonstrate intermedi-

ate levels of bi-parietal activation.(e.g. Subj03 and

Subj04).

Additionally we measured the signal quality us-

ing the negative correlation (Cui et al., 2010) which

shows neurovascular coupling for each subject. Pair

t-test shows that for Subj03 (p < .001) and Subj04

(p < .001) there is signiﬁcant PPC activation in 2D

visual condition respect to 3D visual condition dur-

ing the hand-eye coordination task. Moreover, this

test shows that for Subj01 (p < .001), Subj02 (p <

.05) and Subj03 (p < .001) there is a statistically

signiﬁcant different activation between 3D and 2D

visual condition during depth perception task. The

PPC activation is statistically different between hand-

eye coordination and depth perception task for all the

subjects (two-sample t-test, p < .001). In general,

the concentration of oxyhemoglobin (HbO

) and to-

tal hemoglobin (HbT) is increased and the deoxyhe-

moglobin (HbR) is decreased in bilateral PPC pari-

etal cortex during both the tasks (depth perception

and hand-eye coordination) with respect to the rest-

ing state.

DOES IT EXIST A LINK BETWEEN PERFORMANCE AND PARIETAL CORTEX ACTIVITY IN SURGICAL

TASKS?

383

4 DISCUSSION

This paper raises interesting questions regarding the

possibility of a link between hand-eye coordina-

tion and depth perception capability during surgical

robotics. (i) May the right PPC function to visually

assess and judge an objects depth in space? (ii) May

the left PPC help to guide goal- directed complex vi-

suomotor behaviors? (iii) Are more skilled perform-

ers operating using enhanced PPC neuronal resources

compared to those with poorer technical ability and

error prone performance. (iv) Is the performance

improvement from 2D (traditional laparoscopy) ver-

sus 3D (stereoscopic robotics) secondary to improved

depth perception mediated cortically by the PPC at

the visual/parietal level? A far larger study cohort and

a more detailed analysis would be required to clarify

these ﬁndings.

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