Functional prefrontal reorganization accompanies learning-associated refinements in surgery: A manifold embedding approach

Figures & data

Figure 1. Schematic illustration demonstrating a surface NIR light emitter coupled to a low-light-sensitive detector. The cortical hemodynamic change from a banana-shaped volume of tissue between the emitter and detector is probed non-invasively. Application of a series of emitters and detectors results in hemodynamic recordings from multiple cortical sites (channels) simultaneously.

Figure 2. The experimental set-up. Schematic illustration of a study subject engaged in a knot-tying drill. The electromagnetic pulse emitter is shown on the table in front of the knot-tying jig and motion-tracking sensors are visible on the dorsum of the subject's hands. The figure illustrates the 3 × 3 arrangement of NIRS optodes and the relative positions of NIR emitters (red) and detectors (blue). Optode location is obtained by transferring topographic data from a representative subject to a 3D cortical surface image of a high-resolution T1-weighted MRI image. The two subplots illustrate the location of NIR channels (shaded circles) on the cortical surfaces. The approximate International 10-10 landmarks are highlighted (yellow boxes). [Color version available online.]

Figure 3. Schematic illustration demonstrating the application and flow of the FR-Isomap data embedding technique.

Table I.  Comparison of knot-tying performance according to expertise. Data are presented as median [range]. Significant p-values ≤ 0.001 are in bold.

Parameter	Consultants	Registrars	P	Consultants	Novices	P	Registrars	Novices	P
Time (sec)	12.1 [7.0 to 23.7]	12.3 [7.9 to 23.6]	0.499	12.1 [7.0 to 23.7]	45.5 [21.0 to 149.0]	0.000	12.3 [7.9 to 23.6]	45.5 [21.0 to 149.0]	0.000
TPL	5.2 [2.9 to 9.3]	4.7 [1.9 to 10.4]	0.289	5.2 [2.9 to 9.3]	15.0 [5.5 to 12.6]	0.000	4.7 [1.9 to 10.4]	15.0 [5.5 to 12.6]	0.000
TM	13.0 [2.9 to 9.3]	13.0 [6.0 to 23.0]	0.566	13.0 [2.9 to 9.3]	29.0 [10.0 to 91.0]	0.000	13.0 [6.0 to 23.0]	29.0 [10.0 to 91.0]	0.000

Table II.  Comparison of knot-tying performance in medical students before and after a week of practice. Data are presented as median [range]. Significant p-values ≤ 0.001 (Wilcoxon Sign Rank test) are in bold.

Parameter	1st session	2nd session	P-value
Time	40.0 [18.5 to 257]	17.3 [8.9 to 32.5]	0.000
Total pathlength	9.3 [3.4 to 111]	4.5 [2.9 to 8.5]	0.000
Total movement	21.0 [7.0 to 51.2]	14.0 [9.0 to 20.0]	0.000

Figure 4. (a) Graph depicting residual variance of the fixed references training set in FR-Isomap for fNIRS data from expert and novice surgeons. (b) Diagram of the manifold embedding results for study (A), illustrating the distribution of channel responses and how it varies along the first two principal dimensions for all subjects studied. Locations of the original signals (a–f) are marked on the embedded space, demonstrating the intrinsic trend captured by the embedding technique. (Originally published in reference [12]. Reprinted with permission from Springer Science and Business Media.) (c) The intensity plot of change in total hemoglobin (HbT) demonstrates regions of the embedding most likely to represent brain activation. [Color version available online.]

Figure 5. Manifold embedding results depicting practice-dependent reorganization of cortical behavior in surgical novices. Data represents 74-D trial HbO₂ and HHb values for a given channel and subject. Trajectories illustrate the transition between first-session data (pink crosses) and second-session data (green circles).

Figure 6. Using the k-means algorithm, the central point (centroid) for each group was located in the embedded space. The average distance between each centroid and all other points for that group was calculated (colored spheres), and the distance to the farthest point (cross) is shown as a solid line. [Color version available online.]

Figure 7. (a) Between-group Earth Mover's Distance (EMD) results for study (A); and (b) comparison between studies (A) and (B). [Color version available online.]

Table III.  Results of a random effect model for learning-related changes in (a) ΔHbO₂, (b) ΔHHb and (c) ΔHbT in surgical novices. s.e = standard error. Significant p-values < 0.01 are in bold, and significant values < 0.001 are in bold italics.

		Coefficient	s.e.	z	P > |z|	95% CI
(a) ΔHbO2
	Session	−4.6815	0.6781	−6.90	<0.001	−6.0101 to −3.3524
	Channel	−0.1199	0.0471	−2.54	<0.01	−0.2123 to −0.0275
	Constant	15.2682	1.7404	8.77	<0.001	11.8569 to 18.6794
	σu	5.3868
	σe	8.7670
	rho (fraction of variance due to uj)	0.27407
(b) ΔHHb
	Session	0.8192	0.3074	2.66	<0.01	0.2167 to 1.4217
	Channel	−0.0728	0.0215	−3.39	<0.001	−0.1148 to −0.0307
	Constant	1.4402	0.6783	2.12	0.034	0.1109 to 2.7696
	σu	1.6899
	σe	3.9842
	rho (fraction of variance due to uj)	0.1525
(c) ΔHbT
	Session	−3.8252	0.8353	−4.58	<0.001	−5.4624 to −2.1881
	Channel	−0.1924	0.5813	−3.31	<0.001	−0.3064 to −0.0785
	Constant	16.6534	2.0240	8.23	<0.001	12.6863 to 20.6204
	σu	5.8764
	σe	10.8153
	rho (fraction of variance due to uj)	0.2279

Leff DR, Orihuela-Espina F, Atallah L, Darzi A, Yang GZ. Functional near infrared spectroscopy in novice and expert surgeons–a manifold embedding approach. Proceedings of the 10th International Conference on Medical Image Computing and Computer-Assisted Intervention (MICCAI 2007), N Ayache, S Ourselin, A Maeder. Brisbane, Australia, October 2007. Part II. Lecture Notes in Computer Science 4792., Springer, Berlin 2007; 270–277

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