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RESEARCH ARTICLE
Intelligence-Augmented Rat Cyborgs in Maze
Solving
Yipeng Yu
1
, Gang Pan
1
*, Yongyue Gong
1
, Kedi Xu
2
, Nenggan Zheng
2
, Weidong Hua
1
,
Xiaoxiang Zheng
2
, Zhaohui Wu
1
1College of Computer Science and Technology, Zhejiang University, Hangzhou, Zhejiang, China, 2Qiushi
Academy for Advanced Studies, Zhejiang University, Hangzhou, Zhejiang, China
*gpan@zju.edu.cn
Abstract
Cyborg intelligence is an emerging kind of intelligence paradigm. It aims to deeply integrate
machine intelligence with biological intelligence by connecting machines and living beings
via neural interfaces, enhancing strength by combining the biological cognition capability
with the machine computational capability. Cyborg intelligence is considered to be a new
way to augment living beings with machine intelligence. In this paper, we build rat cyborgs
to demonstrate how they can expedite the maze escape task with integration of machine
intelligence. We compare the performance of maze solving by computer, by individual rats,
and by computer-aided rats (i.e. rat cyborgs). They were asked to find their way from a con-
stant entrance to a constant exit in fourteen diverse mazes. Performance of maze solving
was measured by steps, coverage rates, and time spent. The experimental results with six
rats and their intelligence-augmented rat cyborgs show that rat cyborgs have the best per-
formance in escaping from mazes. These results provide a proof-of-principle demonstration
for cyborg intelligence. In addition, our novel cyborg intelligent system (rat cyborg) has great
potential in various applications, such as search and rescue in complex terrains.
Introduction
Within the past two decades, bio-robots have been realized on different kinds of creatures,
such as cockroaches [1], moths [2], beetles [3], and rats [4–7]. They are expected to be superior
to traditional mechanical robots in mobility, perceptivity, adaptability, and energy consump-
tion [8–11]. Among them, rat robots are becoming popular for their good maneuverability. To
make a rat robot, a pair of micro electrodes are implanted into the medial forebrain bundle
(MFB) of the rat’s brain, and the other two pairs are implanted into the whisker barrel fields of
left and right somatosensory cortices (SI). After the rat recovers from the surgery, a wireless
micro-stimulator is mounted on the back of the rat to deliver electric stimuli into the brain
through the implanted electrodes. This allows a user, using a computer, to deliver stimulus
pulses to any of the implanted brain sites remotely. Stimulation in MFB can excite the rat robot
by increasing the level of dopamine in its brain, and stimulation in the left or right SI makes
the rat robot feel as if its whiskers are touching a barrier. Before a rat robot is used for
PLOS ONE | DOI:10.1371/journal.pone.0147754 February 9, 2016 1/18
OPEN ACCESS
Citation: Yu Y, Pan G, Gong Y, Xu K, Zheng N, Hua
W, et al. (2016) Intelligence-Augmented Rat Cyborgs
in Maze Solving. PLoS ONE 11(2): e0147754.
doi:10.1371/journal.pone.0147754
Editor: Nanyin Zhang, Penn State University,
UNITED STATES
Received: June 18, 2015
Accepted: January 7, 2016
Published: February 9, 2016
Copyright: © 2016 Yu et al. This is an open access
article distributed under the terms of the Creative
Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are
credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information files.
Funding: This work has been supported by National
Key Basic Research Program of China
(2013CB329504) (http://www.973.gov.cn/English/
Index.aspx), Zhejiang Provincial Natural Science
Foundation of China (LR15F020001) (http://www.
zjnsf.gov.cn/), and Program for New Century
Excellent Talents in University (NCET-13-0521)
(http://www.moe.gov.cn/). The funders had no role in
study design, data collection and analysis, decision to
publish, or preparation of the manuscript.
navigation, a training process is usually needed to reinforce the desired behaviors (i.e. moving
ahead, turning left and turning right). In this process, the MFB stimulation acts as a reward as
well as a cue to move ahead, and the left and right SI stimulation act as the cues to turn left and
turn right respectively. In order to get the reward, the rat robot will learn to do the correct
behaviors corresponding to the cues. The references [4,12,13] provide more details. After suf-
ficient navigation training, the rat robot will move ahead in response to the Forward cue, turn
left in response to the Left cue, and turn right in response to the Right cue. In this paper, the rat
robot is referred to as rat cyborg.
One of the reasons that researchers take interest in developing rat cyborgs is that rats have
outstanding spatial localization abilities. They can find a way in an environment by orienting
themselves in relation to a wide variety of cues, including distal cues, typically provided by
vision, audition, and olfaction, as well as proximal cues, typically provided by tactile, kines-
thetic, and inertial systems [14]. Rats even have a well-developed magnetic compass sense for
spatial orientation [15–17]. Rats do not build detailed geometrical representations of the envi-
ronment. They rely on the learnt associations between external perception and the pose belief
created from the self-motion cues. Studies of spatial orientation posit that rats use an “inner
GPS”in hippocampus and entorhinal cortex to create a cognitive map of the environment [18–
22]. Furthermore, RatSLAM, a navigation model which is inspired by rat’s brain, can perform
simultaneous localization and mapping in real time on a mechanical robot [23–25].
On the other hand, machines (or computers) are efficient in numerical computation, infor-
mation retrieval, statistical reasoning, and have almost unlimited storage. Different to rats,
machines have their own methods to explore and learn about the environment in spatial navi-
gation problems. They can capture many categories of information from the environment
through various sensors, such as range sensors, visual sensors, vibration sensors, acoustic sen-
sors, and location sensors. The information is saved and converted into a discrete and digital
form. Then the processed information will be synthesized to map the environment by different
paradigms [26,27]. Eventually, machines can choose various searching algorithms in path
planning, for example, flood-fill method, Dijkstra’s algorithm, Asearch algorithm, rapidly
exploring random tree, probabilistic roadmap. Machines run the sense process, map process,
and decision process in real time and in parallel. A typical demonstration of machine’s naviga-
tion abilities is the micromouse competition, in which a small rat-like mechanical robot
explores a 16×16 maze [28].
For a specific application, biological creatures and machines both have their own strengths
and weaknesses. In this paper, we ask the question: can biological intelligence be augmented
with the help of machine intelligence? To explore the question, a maze solving task was intro-
duced, in which three kinds of subjects (computer, rats and rat cyborgs) were asked to find
their ways from a predetermined starting position to a predetermined target position. It is a
challenge to embed the machine’s maze solving capability into their navigation. In our experi-
ments, the computer traversed the mazes based on an improved wall follower approach, six
rats traversed 14 mazes one by one all by themselves, and then traversed the 14 mazes again in
the same order with the assistance of the computer. Performance was measured by steps, cover-
age rates, and time spent, allowing for comparisons.
Materials and Methods
Subjects
Six rats (adult Sprague Dawley rats; 290 350 g) took part in the experiments over the course of
one month. All of the six rats (named DH12, SV15, SV17, MV12, M01 and M03) had already
gone through a sufficient navigation training process, which means they would turn left in
Rat Cyborgs in Maze Solving
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Competing Interests: The authors have declared
that no competing interests exist.
response to the Left stimulus, turn right in response to the Right stimulus, and move ahead in
response to the Forward stimulus. Note that in this study, Left and Right stimuli are used to
instruct the rat cyborgs to turn left and right, as well as to prevent them from moving into dead
roads. Forward stimulus is not used to instruct them to move ahead, but to reward them. In our
experiments, the six rats and the six rat cyborgs are the same rats. A rat solving mazes by itself is
called a rat, while the same rat solving mazes with the assistance of computer via its backpack
stimulator is called a rat cyborg. This study was approved by the Ethics Committee of Zhejiang
University (Agreement number: Zju201402-1-02-034). All of the rats used in these experiments
were well cared for by the animal keepers. All of the experiments were performed in accordance
with the guidelines issued by the Ethics Committee of Zhejiang University, and they complied
with the China Ministry of Health Guide for the Care and Use of Laboratory Animals.
Apparatus
The experimental system for maze solving is shown in Fig 1. The maze is made of wood, and
comprises 10×10 unit squares (15 cm×15 cm per unit square). Walls of this maze are also 15
cm high and the outside walls enclose the entire maze. The maze is covered with a piece of per-
spex on the top, which is used to prevent rats from climbing and escaping. The starting posi-
tion S is in the bottom-left cell of the maze, and target position G is in the top-right cell of the
maze. A notable feature of this maze is that the four walls of each cell can be inserted or
removed. Therefore we can change the layout of each maze, and set various paths from S to G.
In our experiments, we designed 14 mazes (maze 1 to maze 14, see S1 Fig) with different levels
of complexity. Furthermore, there were a box of peanut butter and a dish of water in the target
cell. The peanut butter was used as an odor source, and the water was used as a reward.
The whole experimental process was captured by a web camera. The camera we used could
capture video clips at a rate of 15 frames per second, with a resolution of 640 by 480 pixels. The
computer acquired the explored maze information and motion states of the rats in real time
with the assistance of the camera. The computer-aided maze solving system running on the
computer was implemented in C++ with a user-friendly interface. Left, Right and Forward
Fig 1. Experimental system for maze solving.
doi:10.1371/journal.pone.0147754.g001
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stimuli were sent to the backpack of a rat via Bluetooth. Left and Right stimuli were sent to
guide the rats only in the maze solving procedure by rat cyborgs. Forward stimulus acted as
another reward (like water) after the rats reached the target cell in maze solving procedures by
rats and by rat cyborgs.
Procedures
Maze Solving Training. In this procedure, in order to get the rewards in the target cell,
rats had to learn to find a path from the constant starting position to the constant target posi-
tion. We used double rewards to reinforce rat’s maze solving behavior: water reward and elec-
tric reward of MFB stimulation. Water is a natural reward, which is indispensable to rats. MFB
reward is a train of short-duration pulses, which can excite the rats. A combination of water
reward and MFB reward can accelerate this maze solving training procedure [29,30]. In addi-
tion, olfactory cues can be an aid for the rats in solving spatial problems [31–34]. In our experi-
ments, a box of peanut butter was placed in the target cell (see Fig 1), which was used to help
rats locate the target cell, and activate their odor tracking abilities.
The detailed training procedure is as follows. After water deprivation for 24 hours, six rats,
which had been well trained in the navigation training, proceeded to the maze solving training,
which consisted of 3 to 5 random mazes per day in consecutive days. The training time in each
day was 8-12 a.m. and 2-6 p.m. In each maze, at first the rat was placed in the constant starting
cell. It had to learn to find a path to the target cell by itself. After the rat arrived at the target cell
and drank a drop of water (0.15 ml) in a dish, five consecutive MFB rewards were sent. Each
rat ran each maze only one time, and each maze had a different layout. Once all of the six rats
finished a maze, they proceeded to training in the next maze. Each rat was offered only 6 ml
water after one day’s training. This amount of water was to meet the basic need, but not enough
to completely satisfy a rat. The rat still wanted to drink water on the next day. The entire train-
ing lasted 7 days. After this procedure, all of the six rats had a strong desire to run in the mazes
to search for the water and MFB rewards.
Maze Solving by Computer. Similar to rats, the computer had to find a path from the
start to the target with no knowledge of the mazes. There are a number of different maze solv-
ing algorithms, such as random mouse, wall follower, Pledge, and Tremaux’s algorithm [35,
36]. In this study, on the basis of dead road detection and unique road detection, two wall fol-
lower rules (left-hand and right-hand) were adopted to traverse the 14 mazes. Dead roads refer
to roads that can not lead to the target. There are two kinds of dead roads: visited dead road
and non-visited dead road. The dead road detection algorithm is listed in Algorithm A in S1
File. A unique road refers to the only way to the target. The detailed unique road detection
algorithm is listed in Algorithm B in S1 File. The complete maze solving algorithm is listed in
Algorithm 1. For left-hand rule, the traversal sequence is clockwise (left!front!right!back),
and for right-hand rule, the traversal sequence is anticlockwise (right!front!left!back). Fig
2shows two maze solving processes by our algorithm. Steps and coverage rates of maze solving
in the 14 mazes were recorded. We took the average steps and average coverage rates of the
left-hand rule and right-hand rule as the performance measures. Two demo videos of maze
solving by our algorithm are presented (Videos A and B in S2 File).
Algorithm 1: Maze solving by our algorithm (left-hand).
1while the current cell C is not the target cell do
2if there is a unique cell U which is accessible in the four adjacent cells
then
3 move to U;
4end
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5else if the left cell of C is accessible and not a dead cell then
6 move to the left cell;
7end
8else if the front cell of C is accessible and not a dead cell then
9 move to the front cell;
10 end
11 else if the right cell of C is accessible and not a dead cell then
12 move to the right cell;
13 end
14 else if the back cell of C is accessible and not a dead cell then
15 move to the back cell;
16 end
17 end
To ensure that our algorithm can reflect the computer’s maze solving capacity, we compare
its performance in 24 mazes (maze 1 to maze 24, see S1 Fig) with that of three classical maze
solving algorithms (i.e. wall follower, Pledge and Tremaux’s algorithm). The experimental
results are presented in Fig 3. We can see from the left column that both the steps and coverage
rates of our algorithm in most mazes are less than those of the other three algorithms. From
the right column, the average steps and average coverage rates of our algorithm are less than
those of the other three algorithms. The statistical analysis (two-tailed paired t-test) also shows
that there are significant differences of the steps and coverage rates between our algorithm and
the other three algorithms (p<0.001). The results indicate that our algorithm outperforms the
other three algorithms in maze solving. Thus we take the performance of our algorithm as
computer’s performance in maze solving, and compare it with that of rats and rat cyborgs.
Maze Solving by Rats. After the maze solving training, the entire maze was washed and
dried, and then the six rats proceeded to this formal maze solving procedure. In this procedure,
the rats solved 14 mazes one by one using their own spatial learning abilities. Details of this
procedure are similar to the maze solving training procedure. The experimental time in each
day was 8-12 a.m. and 2-6 p.m. Each rat ran each maze only one time. In each maze, at first the
rat was placed in the constant starting cell. After the rat arrived at the target cell and drank a
Fig 2. Maze solving by our algorithm. The yellow cell is the current position of the explorer. Blue cells
indicate a unique road to the target. Cyan cells are cells which have not been explored, and walls of these
cells now are unknown to the explorer. Pink slash (“n”) denotes the non-visited dead road, red cross (“×”)
denotes the visited dead road. (a) Left-hand. (b)Right-hand.
doi:10.1371/journal.pone.0147754.g002
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drop of water (0.15 ml) in a dish, five consecutive MFB rewards were sent. Once all of the six
rats finished a maze, they proceeded to solve the next maze. Each rat was offered 6 ml water at
the end of one day’s experiment. Steps, coverage rates and time spent of maze solving by the
rats in the 14 mazes were analysed. Additionally, we observed that the strategy rats took to
solve the mazes was not easily understood (in other words, it was not perfect). They revisited
the visited cells, explored the dead roads which could be easily detected by the computer, and
even returned to the starting cell when they were confused. This offered an opportunity to the
computer to help rats in maze solving. A demo video of this procedure is shown in Video C in
S2 File.
Maze Solving by Rat Cyborgs. A rat cyborg is a computer-aided rat, which is a combina-
tion of a rat and machines. After the procedure of maze solving by rats, the entire maze was
washed and dried, and then the same six rats traversed the 14 mazes in the same order with the
computer’s help. Details of this procedure are similar to the procedure of maze solving by rats,
except that the rats have the help of the computer to solve the mazes. Fig 4 shows two maze
solving processes by rat cyborgs. With the motivation to help rats solve the mazes, the com-
puter tracked the rats, analyzed the explored maze information, and decided when and how to
intervene. The computer aided the rats under three rules: (1) if there was a path to the unique
road, the computer would find the shortest path, then Left and Right commands would be sent
to navigate the rat to the unique road; (2) if the rat was going to enter a dead cell, Left or Right
Fig 3. Steps and coverage rates of maze solving by our algorithm, wall follower, Pledge and Tremaux’s algorithm. Results are presented as mean±s.
e.m. on the right. *p<0.05, **p<0.01, ***p<0.001.
doi:10.1371/journal.pone.0147754.g003
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commands would be sent to prevent such a move; (3) if the rat was in a loop (detected by Algo-
rithm C in S1 File), the computer would find the shortest path to the current destination, then
Left and Right commands would be sent to navigate the rat to follow the path. In this experi-
ment, the computer automatically analyzed the dead roads, unique roads, loop roads and
shortest roads in real time, and generated the guiding information to overlay on the live video,
which is playing on the screen of the computer. At the same time, an expert was watching the
guiding information shown on the screen and sent the Left and Right commands to direct the
rat under the three rules. The sent Left and Right commands were also shown simultaneously
in the video. Please note that the expert was not directly involved in the maze solving, his/her
operations to send the Left and Right commands under the guidance of the computer is just a
simple replacement of the computer’s execution (action), not an augmentation or a diminution
of the intelligence, since all the path detection are performed by the computer. Apart from the
above three rules, rats solved the mazes of their own free will. We did not treat rats as machines
which were totally controlled by the computer. Steps, coverage rates and time spent of maze
solving by the rat cyborgs in the 14 mazes were analysed. A demo video of this procedure is
shown in Video D in S2 File.
Algorithm 2: Rat cyborg tracking algorithm.
1 Save a background image to I
a
;
2while the rat cyborg has not reached the target cell G do
3 pick an image I
b
from the camera;
4 use cvAbsDiff to subtract I
a
from I
b
, write the difference to I
c
;
5 use cvThreshold to get a binary image I
d
from I
c
;
6 use cvFindContours to find all of the contours C
o
in I
d
;
7 search the largest contour C
max
in C
o
;
8 calculate the centroid of pixels in C
max
, write it to the body position R
b
;
Fig 4. Maze solving by rat cyborgs. The red point is the body position, the black point is the head position,
and the blue line is the heading direction of the rat cyborg. Our rat cyborg tracking method (see Algorithm 2) is
implemented by OpenCV. Blue cells indicate a unique road to the target. Red cells are cells which have not
been explored, and walls of these cells now are unknown to the rat cyborg. The pink slash (“n”) denotes the
non-visited dead road, the red cross (“×”) denotes the visited dead road, and the yellow “g”denotes entrances
to the unexplored area. Consecutive blue points indicate the shortest path to the current destination. The
shortest path is detected by A*algorithm [37].
doi:10.1371/journal.pone.0147754.g004
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9 use cvGoodFeaturesToTrack to detect corners in C
max
find a 40×40 square
S
o
in C
max
;
10 find a 40×40 square S
o
in C
max
, which has the most corners;
11 calculate the centroid of corners in S
o
, write it to the head position R
h
;
12 end
Results
In this section, the experimental results of maze solving by computer, by rats and by rat cyborgs
are presented. We first compare steps and coverage rates of maze solving among them. Then
we compare time spent of maze solving between rats and rat cyborgs. Finally, correlation
between the steps and correlation between the coverage rates are analyzed.
Steps
Steps are the sum of times visiting each cell. A cell can be visited multiple times. Steps of maze
solving by the six rats/rat cyborgs are presented with those by the computer in Fig 5. We can
see from the left column that the steps of rat cyborgs in most mazes are less than those of rats,
and may be equivalent to those of the computer. From the right column, the average steps of
each rat cyborg are less than that of each corresponding rat: DH12 (from 117.71±25.70 to
78.64±14.94), SV15 (from 92.57±15.28 to 64.43±9.12), SV17 (from 80.43±12.92 to 67.36
±8.41), MV12 (from 112.86±8.74 to 82.86±4.96), M01 (from 134.00±21.53 to 69.29±9.88), and
M03 (from 156.43±33.92 to 64.57±10.06); and the average steps of the computer (77.79±4.90)
are also less than that of each rat. The two-tailed paired t-test shows that between computer
and rats, there are three rats (i.e. MV12, M01 and M03) that performed worse than the com-
puter; between computer and rat cyborgs, there are no statistically significant differences; and
between rats and rat cyborgs, there are five rats (i.e. DH12, SV15, MV12, M01 and M03) that
performed better with the assistance of the computer. These results suggest that in maze solv-
ing, based on the steps, the performance of rat cyborgs is better than that of individual rats, and
comparable to that of individual computer.
Coverage Rates
Coverage rate is the number of visited cells. Every visited cell is counted only one time, so the
maximum value of the coverage rate is 100. The larger the coverage rate is, the less efficient the
maze solving is. It can evaluate the performance of the explorer in maze solving from another
point of view. Coverage rates of maze solving by the six rats/rat cyborgs are presented with
those by the computer in Fig 6. We can see from the left column that the coverage rates of rat
cyborgs in most mazes are less than those of the computer and those of the rats. From the right
column, the average coverage rates of each rat cyborg are less than that of each corresponding
rat: DH12 (from 58.71±6.59 to 52.21±6.89), SV15 (from 55.36±6.26 to 51.71±6.84), SV17
(from 53.57±7.06 to 51.64±6.35), MV12 (from 60.36±5.25 to 54.57±5.20), M01 (from 65.07
±5.86 to 52.71±6.92), and M03 (from 64.86±7.27 to 51.07±6.92); and the average coverage
rates of each rat cyborg are also less than that of the computer (60.50±5.13). The two-tailed
paired t-test shows that between computer and rats, there are no statistically significant differ-
ences; between computer and rat cyborgs, all of the six rat cyborgs performed better than the
computer; and between rats and rat cyborgs, there are four rats (i.e. DH12, MV12, M01 and
M03) that performed better with the assistance of the computer. These results suggest that in
maze solving, based on the coverage rates, the performance of rat cyborgs is better than that of
individual computer and that of individual rats.
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Time Spent
Time spent measures the period between a rat/rat cyborg starts to move at S and the rat/rat
cyborg reaches G. Besides steps and coverage rates, we further compare the time spent of the
rats in the 14 mazes with those of the rat cyborgs. Time spent of maze solving by the six rats/
rat cyborgs are presented in Fig 7. As we can see from the left column that the time spent of rat
cyborgs in most mazes are less than those of rats. From the right column, the average time
spent of each rat cyborg is less than that of each corresponding rat: DH12 (from 168.07±44.95
to 129.36±32.74), SV15 (from 347.43±68.68 to 125.00±31.48), SV17 (from 328.50±40.19 to
253.43±31.69), MV12 (from 588.43±106.85 to 333.07±61.58), M01 (from 156.14±33.13 to
Fig 5. Steps of maze solving by computer, rats and rat cyborgs. The steps of maze solving by DH12, SV15, SV17, MV12, M01 and M03 are shown from
the top to the bottom, respectively. Data are presented as mean±s.e.m. on the right. *p<0.05, **p<0.01, ***p<0.001.
doi:10.1371/journal.pone.0147754.g005
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70.50±8.82), and M03 (from 144.36±36.35 to 45.14±13.96). The two-tailed paired t-test shows
that there are four rats (i.e. SV15, MV12, M01 and M03) that performed better with the assis-
tance of the computer. These results suggest that in maze solving, based on the time spent, the
performance of rat cyborgs is better than that of individual rats.
Fig 6. Coverage rates of maze solving by computer, rats and rat cyborgs. The coverage rates of maze solving by DH12, SV15, SV17, MV12, M01 and
M03 are shown from the top to the bottom, respectively. Data are presented as mean±s.e.m. on the right. *p<0.05, **p<0.01, ***p<0.001.
doi:10.1371/journal.pone.0147754.g006
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Correlation
The 14 mazes have different levels of complexity from the human perspective, and the more
complicated mazes should consume more steps to solve. Maze 11 was supposed to be the most
complicated maze among the 14 mazes, and it took the rats exceptionally many more steps (see
Fig 5). Firstly, we analyze the Pearson’s correlation coefficients of steps and coverage rates
Fig 7. Time spent of maze solving by rats and rat cyborgs. The time spent of maze solving by DH12, SV15, SV17, MV12, M01 and M03 are shown from
the top to the bottom, respectively. Data are presented as mean±s.e.m. on the right. *p<0.05, **p<0.01, ***p<0.001.
doi:10.1371/journal.pone.0147754.g007
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between each other within the six rats/rat cyborgs (see Fig 8). In terms of steps, except MV12,
the other five rats/rat cyborgs have a positive correlation between each other in maze solving.
In terms of coverage rates, all of the six rats/rat cyborgs have a positive correlation between
each other in maze solving. These results indicate that a maze that is difficult for a rat/rat
Fig 8. The Pearson’s correlation coefficients of steps and coverage rates between each other within the six rats/rat cyborgs. (a) Correlation
coefficients of steps within the six rats. (b) Correlation coefficients of steps within the six rat cyborgs. (c) Correlation coefficients of coverage rates within the
six rats. (d) Correlation coefficients of coverage rates within the six rat cyborgs.
doi:10.1371/journal.pone.0147754.g008
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cyborg should be difficult for other rats/rat cyborgs as well. Secondly, we further analyze the
Pearson’s correlation coefficients of steps and coverage rates between computer and rats, com-
puter and rat cyborgs, and rats and the corresponding rat cyborgs (see Table 1). In terms of
steps, all of the correlation coefficients are strong positive, except those between MV12 and the
computer. In terms of coverage rates, all of the correlation coefficients are strong positive.
These results indicate that a maze which is difficult for a rat should be difficult for the corre-
sponding rat cyborg and computer as well, and vice versa.
Discussion
The experimental results show that, in terms of steps, coverage rates and time spent, rat
cyborgs performed better than rats in maze solving. However, in terms of steps, performance
of rat cyborgs did not show remarkable advantages over that of computer. Actually, rats did
not strive to reach the destination in the least number of steps. They sometimes would revisit
visited cells again and again, and wander between adjacent cells. Nonetheless, all of the six rat
cyborgs outperformed the computer in terms of the coverage rates. Moreover, the rat cyborgs
are agile in different types of terrain (see S1 Video), and have the potential to solve unantici-
pated problems relying on instinct [38].
Because the six rats and the six rat cyborgs were the same rats, the possible interference
should be carefully prevented. In our experiments, we took four measures to avoid interference:
(1) for a rat and its rat cyborg, the layout of each maze was the same, while the physical walls of
each maze cell were changed; (2) a maze solved by a rat would be solved by its rat cyborg at
least 4 days later, not in the following day; (3) in the interval, the rat would be asked to carry
out experiments with other mazes to further weaken its memory of the previous maze; (4)
between the procedure of maze solving by rats and the procedure of maze solving by rat
cyborgs, the entire maze was washed and dried to remove the possible odor interference. In
order to verify that the performance enhancement of the rat cyborgs in maze solving was not
attributed to what the rats had experienced, we conducted two supplemental experiments.
In supplemental experiment 1, two rats (i.e. M01 and M03) first traversed 5 mazes (maze 15
to maze 19, see S1 Fig) one by one with the assistance of the computer, and then traversed the 5
mazes again in the same order all by themselves. If a strong memory of the mazes has been
gained by the rat cyborgs, it will then benefit the performance of the rats. The experimental
results are shown in Fig 9. As we can see, the steps of each rat cyborg are less than that of the
corresponding rat in each maze. The coverage rates of each rat cyborg are less than that of the
corresponding rat except in maze 17 of M03, the coverage rates of each rat cyborg are less than
that of the computer except in maze 18, and the average coverage rates of each rat cyborg
(M01: 49.40±7.72, M03: 49.20±7.51) are less than that of the corresponding rat(M01: 59.80
±9.68, M03: 56.60±8.35) and the computer (60.00±2.57). Besides, M01 spent less time in maze
Table 1. The Pearson’s correlation coefficients of steps and coverage rates between computer and rats, computer and rat cyborgs, and rats and
rat cyborgs.
DH12 SV15 SV17 MV12 M01 M03
scscsc s cscsc
Computer vs Rats 0.5610 0.8822 0.6524 0.9141 0.4984 0.8951 −0.1137 0.7724 0.5784 0.7966 0.6979 0.7970
Computer vs Rat cyborgs 0.5696 0.9018 0.6653 0.9022 0.6034 0.9059 -0.2160 0.8667 0.7198 0.9399 0.6548 0.9376
Rats vs Rat cyborgs 0.9254 0.9224 0.5469 0.9450 0.7024 0.9005 0.7004 0.9123 0.6302 0.7881 0.5639 0.7350
s is an abbreviation for steps, c is an abbreviation for coverage rates.
doi:10.1371/journal.pone.0147754.t001
Rat Cyborgs in Maze Solving
PLOS ONE | DOI:10.1371/journal.pone.0147754 February 9, 2016 13 / 18
solving with the assistance of the computer except in maze 17. These results show that rat
cyborgs have a better performance than rats. This is consistent with the conclusion of the previ-
ous experiments, and demonstrates that the performance enhancement of the rat cyborgs in
maze solving should not be attributed to what the rats had experienced.
In supplemental experiment 2, two rats (i.e. M01 and M03) first traversed other 5 mazes
(maze 20 to maze 24) one by one all by themselves. Then these 5 mazes were flipped along the
diagonal axis from the entrance to the exit, and traversed by the two rats in the same order
with the assistance of the computer. Note that each pair of the flipped maze and the original
one (see S1 Fig) have the same complexity but different space layouts. In this way, a rat’s mem-
ory of the original maze can hardly help the counterpart rat cyborg solve the flipped maze. The
experimental results are shown in Fig 10. As we can see, the steps of each rat cyborg are less
than that of the corresponding rat in each maze. The coverage rates of each rat cyborg are less
than that of the computer except in maze 24 of M01, and the average coverage rates of each rat
cyborg (M01: 46.00±8.92, M03: 36.40±3.36) are less than that of the corresponding rat(M01:
52.40±7.52, M03: 40.80±7.22) and the computer (56.60±2.96). Besides, M03 spent less time in
maze solving with the assistance of the computer except in maze 21. These results show that rat
cyborgs have a better performance than rats. This is consistent with the conclusion of the
Fig 9. Steps, coverage rates and time spent of maze solving bycomputer, M01 and M03 in maze 15 to maze 19. (a) Steps of maze solving by computer
and M01. (b) Steps of maze solving by computer and M03. (c) Coverage rates of maze solving by computer and M01. (d) Coverage rates of maze solving by
computer and M03. (e) Time spent of maze solving by computer and M01. (f) Time spent of maze solving by computer and M03.
doi:10.1371/journal.pone.0147754.g009
Rat Cyborgs in Maze Solving
PLOS ONE | DOI:10.1371/journal.pone.0147754 February 9, 2016 14 / 18
previous experiments, and also demonstrates that the performance enhancement of the rat
cyborgs in maze solving should not be attributed to what the rats had experienced.
Thanks to the rapid advance of brain-machine interfaces (BMIs), the connection and inter-
action between the organic components and computing components of the cyborg intelligent
systems are becoming deeper and better [39–43]. Based on such kinds of symbiotic bio-
machine systems, a new type of intelligence, which we refer to as cyborg intelligence, will play
an increasingly crucial role. Cyborg intelligence is a convergence of machine and biological
intelligence, which is capable of integrating the two heterogeneous intelligences at multiple lev-
els [44,45]. It has the potential to deliver tremendous benefits to society, such as in search and
rescue, health care, and entertainment. In this work, the mobility, perceptibility and cognition
capability of the rats were combined with the sensing and computing power of the machines in
the rat cyborg system. The experimental results of the rat cyborg system in maze solving pro-
vide a proof-of-principle demonstration for cyborg intelligence.
Conclusions and Future Work
In this paper, we build intelligence-augmented rat cyborgs and present a comparative study of
maze solving by computer, by rats, and by rat cyborgs. Computer aids rats in dead road detec-
tion, unique road detection, loop detection, and shortest path detection. In terms of steps, cov-
erage rates and time spent, the rat cyborgs have a better performance than the individual rats
in maze solving; in terms of coverage rates, the rat cyborgs have a better performance than the
Fig 10. Steps, coverage rates and time spent of maze solving bycomputer, M01 and M03 in maze 20 to maze 24. (a) Steps of maze solving by
computer and M01. (b) Steps of maze solving by computer and M03. (c) Coverage rates of maze solving by computer and M01. (d) Coverage rates of maze
solving by computer and M03. (e) Time spent of maze solving by computer and M01. (f) Time spent of maze solving by computer and M03.
doi:10.1371/journal.pone.0147754.g010
Rat Cyborgs in Maze Solving
PLOS ONE | DOI:10.1371/journal.pone.0147754 February 9, 2016 15 / 18
individual computer in maze solving. From the systematic perspective, the rat’s capability of
maze solving has been augmented by the computer.
In future work, more tasks will be introduced, and the complexity of tasks will be quantified.
To avoid excessive intervention with the rats, the strength of the computer’s assistance will be
graded. In addition, more practical rat cyborgs will be investigated: the web camera will be
replaced by sensors mounted on rats, such as tiny camera, ultrasonic sensors, infrared sensors,
electric compass, and so on, to perceive the real unknown environment in real time; and the
computer-aided algorithms can be housed on a wireless backpack stimulator instead of in the
computer.
Supporting Information
S1 Fig. Maps of the 24 mazes solved in our experiments. The start is in the bottom-left cell of
each maze, and the target is in the top right-cell of each maze.
(PDF)
S1 File. Dead road detection (Algorithm A). Unique road detection (Algorithm B). Loop
detection (Algorithm C).
(ZIP)
S2 File. Maze solving by computer, rats and rat cyborgs. Computer solved maze 5 by our
algorithm under the left-hand rule (Video A). Computer solved maze 5 by our algorithm
under the right-hand rule (Video B). DH12 solved maze 5 by itself (Video C). DH12 solved
maze 5 with the assistance of the computer (Video D).
(ZIP)
S1 Video. A rat cyborg traversing complex terrain.
(MP4)
S1 Table. Experimental data of maze solving in the 24 mazes (maze 1 to maze 24) by our
algorithm, wall follower, Pledge and Tremaux’s algorithm.
(XLS)
S2 Table. Experimental data of maze solving in the 14 mazes (maze 1 to maze 14) by the
computer and 6 rats/rat cyborgs.
(XLS)
S3 Table. Experimental data of maze solving in the 10 mazes (maze 15 to maze 24) by the
computer and 2 rats/rat cyborgs.
(XLS)
S4 Table. Stimulus parameters of the 6 rats/rat cyborgs.
(XLS)
Acknowledgments
This work is supported by National Key Basic Research Program of China (2013CB329504),
Zhejiang Provincial Natural Science Foundation of China (LR15F020001), and Program for
New Century Excellent Talents in University (NCET-13-0521). The authors are grateful to the
editor and reviewers for their insightful comments. They also are pleased to thank Liqiang
Gao, Liujing Zhuang, Shengzhang Lai for technical support and Chaonan Yu for the rat
surgery.
Rat Cyborgs in Maze Solving
PLOS ONE | DOI:10.1371/journal.pone.0147754 February 9, 2016 16 / 18
Author Contributions
Conceived and designed the experiments: YY GP KX ZW. Performed the experiments: YY
WH YG. Analyzed the data: YY GP YG. Contributed reagents/materials/analysis tools: YY GP
KX NZ XZ. Wrote the paper: YY GP.
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