Hippocampus, theta waves and movement IV

In part III I brought some of the info from Vanderwolf's book to do with movement, types of movement, and their association with hippocampal wave function. On p. 16 he says:

".. in 1962 (we) had shown that rhythmical waves could occur in the thalamus and hippocampus slightly in advance of overt motor activity. ...I had no accurate means of determining the precise instant of movement onset and.. spontaneous movements do not have an abrupt onset. Spontaneous walking, for example, is usually preceded by small head movements and adjustments in posture (intention movements). What was need was an abrupt transition from complete immobility to vigorous gross movement of the type that is consistently accompanied by hippocampal waves."

To solve this problem he designed a box with a metal floor into which a rat could be placed and a small shock delivered to its feet, part of a training process teaching them to jump out of the box; i.e., shock was not part of the experimental design, just the jump-from-inside-the-box training.

"..a trained rat could be placed gently on the floor, standing on its hind legs. After a delay of several seconds during which the rat stood motionless, the hind legs would extend suddenly, propelling the rat to the top of the box. A movement-sensing device mounted on the box recorded the onset of this jump with an accuracy of a few milliseconds."

Vanderwolf found that rhythmical waves of 6-7 Hz could occur several seconds prior to the jump. Beginning about a second before the jump the frequency increased to 8-12 Hz, peaking at jump initiation, continuing until the rat landed on the "safe" shelf.

"The data from this experiment suggested that the hippocampus might have some role in both planning and the performance of a motor pattern. It also suggested a problem which subsequently became a major focus of my research. If the rhythmical waves of the hippocampus are related to motor activity, how is it possible that these waves can be present during relatively long intervals (several seconds) when a rat is absolutely motionless?"

Meanwhile, in a nearby lab the hippocampus of New Zealand white rabbits showed rhythmical activity being elicited with visual and auditory input only, no visible motor activity, something not noted in rats.

REM sleep presented another exception to the idea that hippocampal rhythmical activity was associated with movement, and was noted by Vanderwolf in the late 60's.

"The onset of REM sleep in a rat is always associated with an utter collapse of any pre-existing muscle tone. Thus, if a rat falls asleep in a crouched sitting posture, as they sometimes do, the onset of REM sleep is associated with the body slumping down limply on the floor. Despite this, bursts of muscular twitches occur periodically in the limbs, trunk, and especially in the vibrissae. Rhythmical slow waves occurred in the hippocampus throughout an episode of REM sleep, with higher frequency waves occurring during the muscular twitches than during the inter-twitch intervals. An interpretation of this curious phenomenon was suggested by research originating with Otto Pompeiano of the University of Pisa.It appears that brain motor systems generally are in a state of high activity during REM sleep but that overt expression of this activity is blocked by a powerful inhibition of spinal motor neurons and of reflex afferents to those neurons. Consequently, instead of running, jumping, etc. the animal lies limply on the floor, twitching slightly. The hippocampal record then is related to motor activity during REM sleep as well as during waking."

At this point Vanderwolf teamed with Bob Sainsbury and two students, Brian Bland and Ian Whishaw, to continue the work at U. of Western Ont.

Next: hippocampal slow waves, learning and instinctive behavior.

Hippocampus, theta waves and movement III

A description of the following rat behaviors and accompanying rhythms appears next.


Sleep to waking:

1. Sleep: neocortex waves went from low voltage fast activity to large amplitude, irregular slow waves.

2. Startle out of sleep with a noise: rat

"would leap to its feet, startled, its head up, eyes wide open, then stand motionless."

Large slow waves of the neocortex were replaced by low voltage higher frequency record (neocortical activation) but no rhythmical waves from hippocampus, instead a pattern of irregular waves with low amplitude.

From this Vanderwolf concluded that

"the rhythmical hippocampal waves had nothing to do with arousal or alerting; they were specifically related to a class of movements that did not include the startle response."

During movement:

3. In the waking rat: sensory stimuli generally elicited hippocampal rhythmical slow activity only if they also elicited a certain type of motor activity.

".. a great variety of visual, auditory, tactile and olfactory stimuli elicited both hippocampal rhythmical slow activity and a behavioral response that included head movements, stepping and locomotion."

4. Rats hung vertically by their front paws: No hippocampal activity was recorded while they just hung there, front paws clutched over the top of a vertical board.

"Rhythmical waves always appeared, however, when a rat pulled itself up, climbing to the top of the board."

Vanderwolf concluded that rhythmical hippocampal waves accompany certain phasic movements not static muscular exertion. Furthermore, maintenance of an immobile standing posture on two legs or four, was not associated with rhythmical slow hippocampal activity.


Grooming:

5. Grooming: Rat sits up on hind legs and uses front paws to rub its mouth, face, eyes and whiskers, followed by nibbling of own flanks, hind legs, abdomen. Movements are vigorous, but generally not accompanied by rhythmical hippocampal waves. By contrast, while resting, even just a small movement of one forepaw was regularly accompanied by rhythmical hippocampal waves.

Conclusion: two qualitatively distinct classes of behavior: one accompanied by waves and one not.

6. Grooming: occasional bursts of clear rhythmical waves lasting a second or two at most, occurred during long grooming sessions. They were accompanied by changes in posture, transitions from the rat paying attention to/grooming one area of the body, to paying attention to/grooming another area.

Conclusion: rat grooming behavior consists of two kinds of movement, 1) stereotyped licking, biting fur, rubbing of forepaws over face, without hippocampal slow wave; 2) changes in posture, accompanied by rhythmical slow activity in the hippocampus.

7. Grooming behavior, plus startle: Two possible reactions: rat becomes immobile (freezing behavior) without hippocampal slow wave accompaniment, however, if head movements or locomotion were chosen by the rat, rhythmical waves would appear.


Eating and drinking:

8. Approach to food, snatching it, running off with it: continuous rhythmical waves were recorded.

9. During chewing and handling of food with forepaws: Rhythmical hippocampal activity was present at the onset of eating a large food pellet, but as the pellet got smaller so did the hippocampal activity.

10. Sniffing behavior: vigorous sniffs with small head movements - no associated slow rhythmical wave from hippocampus associated.

11. Approach to/retreat from water dish was accompanied by rhythmical hippocampal waves but not the act of drinking itself.


Exploratory:
12. Rhythmical hippocampal waves were found to have no specific relation to exploratory behavior in general sense. On the other hand, changing posture of head while eating or changing posture while grooming are well-practiced and are accompanied by slow wave activity.

Next, Vanderwolf looked deeper at premotor activity.