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DanceFloor by dynamic artist Jenny James. Copyright 2006 (used with permission)

Evidence That the Forebrain is Responsible for Strategic Actions

by David D. Olmsted (Copyright - 2000, 2006. Free to use for personal and educational purposes)
Last Revised September 4, 2006

Introduction

The forebrain (telencephalon) seems to have the purpose of motivating the animal to seek its ideal surroundings. While the hypothalamus motivates the animal based upon its internal state the forebrain via its septum and amygdala motivates the animal based upon its percieved external state. As such it governs the animal's strategic actions as opposed to its targeted tactical actions governed by the tectum region located at the other end of the hypothalamus.. With this purpose one can see the evolutionary pressures that lead to its further development into the primate neocortex and sub-cortical structures.

Removal of the Forebrain Affects Activity Levels and Strategic Learning

In 1912 Theodore Burnett at the University of California tested frogs with and without their forebrain (cerebral cortex, septum, amygdala) in the testing apparatus known as the labyrinth shown below in figure 1.

Figure 1
The Labyrinth (Burnett - 1912)

Burnett had this to say about these frogs (two Rana pipiens and one Rana boylii):

"Any one casually observing a decerebrate frog would say there was no difference between such a frog and a normal one. But if a normal and a decerebrate frog are observed at the same time it will be seen that there is a difference of degree. The decerebrate frog is somewhat less spontaneous. When a normal and a decerebrate frog were put in the labyrinth together the normal frog would at once start forward in his effort to escape. The decerebrate frog, however, would remain quiet for varying lengths of time before it would start forward. This was rather a drawback to the experiments in the labyrinth as it required constant stimulation to keep the decerebrate frogs moving."
"It was also noticed that the decerebrate frogs spent a great deal more time in the water than did the normal. On several occasions they were taken from the water and placed with the normal frogs. Sometimes they would jump back again without any apparent cause; at other times the slamming of a door or the jarring of the building would be followed by a "plump" as the decerebrate frogs jumped into the water. If a decerebrate frog happened to be 'sitting on the bank', so to speak, and one approached suddenly or made a sudden gesture it would immediately spring into the water, especially if oriented in that direction. If oriented in some other direction the frog might turn but more likely it would spring forward, come into contact with the wall of its habitat, turn, and take to the water. The normal frog, on the contrary, was just as likely to crouch and remain perfectly motionless."

While in the their cage these decerebrate frogs were not able to acquire sufficient food so everyday each one was placed in a glass jar along with many one winged flies and they remained there until all the flies had been eaten. While in a glass jar a decerebrate frog typically remained motionless until a fly came into its field of view. It then turned its head and if the fly kept moving the frog would spring and snap. If the fly stopped nothing would happen. 

The question which Burnett sought to answer was whether a decerebrate frog like a normal frog could learn a path of escape from an unpleasant situation in the labyrinth. The answer was that it could not as explained below:

"As soon as he (a normal frog) entered the labyrinth a drop of ether was let fall upon his back. The frog lost no time in moving on, but went in a straight line to the right side which was closed with glass. Single induction shocks were then sent through the wires, whereupon the frog whirled about and jumped off to the clear space. After sitting quietly for a few minutes he went to the open end and escaped. After about twenty trials this normal frog would make his escape with rarely an error. Occasionally he would make a mistake and go to the glass, but would correct the error on feeling the first shock. In order to be sure this was an association the labyrinth was reversed, the left opening being closed by a glass plate. The frog went straight to the left side as usual and finding his way blocked, tried to 'bore' through the glass. An induction shock was followed by violent efforts to escape through the glass until finally a sudden turn and jump sent him towards the rear end. After sitting for a short time the frog went to the rear end of the labyrinth whence he started. It was quite obvious that he was at a loss how to escape."
"The decerebrate frogs behaved in a very different manner. On entering the labyrinth they would jump forward when stimulated by the ether and generally landed on the wires in the middle of the passage. If the induction shock was weak they would either jump a short distance or crawl forward a short distance. If the current was strong they would give a spring forward and land at the glass, or if oriented toward the open end, as often happened, they would spring to the opening and escape. If stimulated at the glass end they would make frantic efforts to get through or over the glass, until falling backward, they would be oriented toward the rear of the labyrinth. They would then go to the rear end, only to be made uncomfortable by the ether, when back they would go again to the glass."

Over one hundred trails were made with Rana boylii with no improvement in its escape ability.

An Example of Strategic Behavior - Seeking Out Light so as to Catch Bugs

During the winter (October to February) 1902-03 Ellen Torelle at Bryn Mawr looked at the light responses of two species of frogs, Rana virescens and Rana clamata. The frogs were placed in boxes twelve inches long, five inches high, and nine inches wide having a glass window at one end and a door at the other. The inside of the box was painted black.

Response to Diffuse Light at Laboratory Temperature

Frogs were placed at the dark end of the box with their heads pointed away from the light. They usually took 1/4 to 1 minute to reach the light after which they remained at that end looking out.

Response to Direct Light at Laboratory Temperature

"The sunlight fell into one end of the box only. In each case the response was immediate and positive. The animals moved directly to the illuminated end of the box, where they remained a variable length of time, from two to four minutes, when they moved backward, just outside the circle of bright illumination, where they remained until taken away, the median plane of the body being parallel to the incoming ray. In most cases, when the sun illuminated area was small, the head was not turned from the light during the retreat, which was accomplished by moving first one side of the body, then the other, sidewise and backward. In other cases the frogs turned at right angles to the light, hopped outside the area of intense illumination, and oriented themselves with their heads in the direction of the incoming ray."
"Since the retreat into the area of less intense illumination might have been caused by the heat of the sun's rays, the experiments were repeated, heat being cut off by placing a glass vessel ...filled with water close to the glass end of the box. In each case the result was practically the same as before."

Response to Direct Light Outside

Frogs were carried outside on a plate covered by by an opaque bell jar.

"It was deposited three yards from the shadow of the building, the bell jar removed and the frog left on the plate with its head turned away from the sun and from the shadow of the building. The frog first hopped forward, then stopped, turned in the direction of the sun, and hopped well into the shadow where it remained quietly for ten minutes. It was then moved into the sunshine in about its former position. Again it turned and hopped into the shadow. The results were very much the same in the case of each frog tried."

What one seems to have here is movement to the optimum area for catching bugs. Frogs in the shade are partly hidden and not subject to overheating and drying out. In contrast the bugs are illuminated by the sun and stand out with high contrast.

Orientation with One Eye Covered

A hood was attached to the head of a frog such that the left eye was covered and the frog placed in the dark end of the box.

"It immediately turned with its right eye directed toward the source of light, i.e. with its body oblique to the incoming ray. The angle of deviation from the direction of the incoming ray differed in different individuals. Five frogs were tried, but in no case was the orientation that observed when both eyes were covered."

The Effect of Increased Temperature

"A marked acceleration in time of response was noted in temperatures up to and including 25 degree C. The frog moved immediately and directly from the darker end of the box to the lighted end where it remained close to the glass. Between 25 and 30 degrees C the frog became restless and moved about much. Above 30 degrees C movements toward the darker end were as frequent as those toward the lighter end."

The Effect of Lowered Temperature

In a test box at 8 degrees C.

"When a frog was placed in its rear end, head turned from the light, it moved to the light at once, remained there for one-half minute, but retreated, turned away from the light, and remained in the rear of the box, either moving about, its head down as if it were trying to get under something, or quietly crouching, with the head down during the other nine and one-half minutes of the experiment. When returned to the aquarium (15 degrees C.), the above movements continued in the water, the frog remaining for several minutes on the floor of the aquarium. Five frogs were tried; three of these did not leave the rear end of the box at any time."

The normal response of frogs to low temperature is to find a hiding place, preferably under water, were it can rest until warmer temperatures return. The above experiment clearly shows the change in strategic actions due to lower temperatures.

Will this Type of Frog Burrow Under Sand During Cold Temperatures?

Several inches of sand was placed at the bottom of a large water filled jar.

"Twelve frogs were tried. When the temperature of the water in the jar became 10 degrees C. the frogs went down and remained down, with the body flat and limbs outspread, but no attempt was made to burrow. The crouching movements, together with the passing of the head over the surface of the sand as if exercising a sense of touch, continued with a lowering of the temperature to 4 degrees C, when they ceased. When a rock was lowered into the jar in such a way that a small space was formed between it and the wall of the jar, the frog crawled into this space and remained there. When a space was formed between the bottom of the jar and the rock, it crawled into that. This was tested several times."

How Does a Frog Recognize a Shadow?

"The side of a large wooden box was covered with black cloth and the frog placed near the black perpendicular surface. It hopped close to this remained but a couple of minutes, then moved tot he wall of the gray-colored building, where it remained at rest in the angle formed by the wall and the ground. When placed near the uncovered box ... there was no movement towards it. When the box was raised on one edge and propped so that the other edge was about four inches from the ground, the frog moved toward the shadow thus formed, crept well under the box, placed the body between its floor and the ground, where it remained with its head directed outward."
"A black cloth was fastened close to the ground in the center of a sun illuminated area, and a frog placed near it moved onto it, crept along the edge as if seeking cover, then hopped off. A second frog also hopped onto the cloth, but almost immediately moved off."
"Tests were also made at mid-day on a level tract of ground about two acres in extent which contained neither trees nor any object that could cast a shadow. Six frogs were tried. When freed, each moved indifferently toward any point of the compass, but usually kept on moving in the direction in which it began to move. In several trials no movement resulted: the frog crouched low between short bunches of grass, its head held close to the ground."

"Playing Dead" as another Type of Strategic Action

Curtis Riley (1913) at the University of Illinois reported that the toads (Bufo Americanus) with which he was working exhibited a "playing dead" response to rough handling. This response may be triggered by the motion sensors of the inner ear. He describes it this way (page 201):

"The legs are drawn up closely against the body and they assume a more or less rigid condition, the animal remaining motionless. Sometimes a toad lies so absolutely quiet that even the respiratory movements are unobserved, and the eyes may be closed. A young toad may be made to feign death by being placed on its back in the hand or on the laboratory table, and held in that position for a few seconds."
"There is considerable variation among different individuals regarding the length of time of the death-feigning response. Some feign death for a few seconds only, while others retain the death-feigning posture for a minute and occasionally even for a longer time."

Mature specimens of Bufo americanus will also feign death if they are held upside down for approximately 30 seconds, a longer amount of time than is needed for young toads. The frog Rana pipiens can also be made to feign death.

Minimizing Aversive Cost

If a frog is given a light cue it can learn to avoid responding (jumping) to a mild shock while still responding to a large shock. This is significant for in classical conditioning learning an animal would use the light cue to initiate an escape before the shock occurred. The extent of this light inhibition is described by Robert Yerkes (1904 - page 127):

"The inhibitory influence of light in this case depends upon the intensity of the electric stimulus. Even a very strong light will not cause much retardation to a 3 or 4 cell current. As the strength of the electric stimulus decreases the delay of reaction increases, until finally there is complete inhibition. At this point an electric stimulus to which the frog would react almost invariably when there is no disturbing condition will fail to cause reaction in the presence of a sudden increase in light intensity."

(If the battery cells back then are similar to the cells of today each one produces 1.5 volts so 3 to 4 cells connected in series would produce 4.5 to 6 volts)

Table 1 shows how one frog learned to stop responding to the mild shock. The learning was quick yet the frog still occasionally tested whether the shock still occurred by temporarily "forgetting" the association. Table 2 shows the reactions of the same frog a half hour later. It still responds to mild shocks when no preceding light cue is provided but immediately stops when the cue is provided once again. Notice the wide variation in response times. (One wonders if this wide variation would hold with stronger shocks.)

Significantly, the frogs tested by Yerkes were not able to use the sound from an electric bell as a cue indicating that frog brains are not "wired" to make this association.

The frogs in this series of experiments seem to be comparing the aversiveness of its jumping reaction to the aversiveness of the shock. If the shock is mild enough the frog ceases to respond. This minimization of aversive cost is most likely the function of the forebtain’s septum and amgdala. ( A great experiment would be to remove the brain regions and then determine if the shock response can still be inhibited).

Reaction Time of Frog to One Celled Electric Shock Preceded by a Light Cue 2 Seconds Before Shock
Trial NumberReaction Time (ms)
1144
2192
3587
4No Reaction
5No Reaction
6Reaction to 2nd Stimulus
7No Reaction
8No Reaction
9177
10No Reaction
11No Reaction
12No Reaction
131190
14No Reaction
Table 1
Reaction Time of Light Trained Frog to One Celled Electric Shock
Trial Number with no Light CueReaction Time (ms)
1152
2145
3221
4327
5263
6271
7329
8215
9225
10216
11No Reaction
Trial Number with Light Cue -----
11No Reaction
12No Reaction
13No Reaction
14No Reaction
15No Reaction
Trial Number with no Light Cue-----
16216
Table 2

References

Burnett, Theodore C. (1912) Some Observations of Decerebrate Frogs with Special Reference to the Formation of Associations, American Journal of Physiology 30:80-87

Riley, C.F. Curtis (1913) Responses of Young Toads to Light and Contact. The Journal of Animal Behavior 3:179-214

Shaeffer, Asa A. (1911) Habit Formation in Frogs. Journal of Animal Behavior. Vol.1, No. 5, pages 309-355

Torelle, Ellen (1903) The Response of the Frog to Light. American Journal of Physiology. Vol.9, No. 6, Pages 466-488

Yerkes, R.M. (1904) Inhibition and Reinforcement of Reactions in the Frog Rana clamitans. J. Comparative Neurology and Psychology 14:124-137



Web site by David D. Olmsted. He can be contacted at brainsim1-contact at yahoo dot com (this is an anti-spam tactic. Type the address as normal). Original site established August 21, 1998 by David D. Olmsted. New home page published August 25, 2006

Information compiled by David D. Olmsted © 1998 to 2006 (Free to use for personal and educational use)