Electrographic correlates of "inner states" caused by positive conditioned stimuli in the course of instrumental conditioning in dogs

Energy characteristics (power spectra) of short-term (less than 1 s) EEG-reactions were studied in dogs in the course of instrumental conditioning. These reactions were observed in different areas of the cortex during selective attention in response to positive conditioned stimuli. They immediately preceded strong blow with a paw on the pedal of feeding cup and taking the reward. The EEG power at these moments was 1.5-3 times higher than the baseline EEG power level in a prestimulus period. The high-frequency structure of corresponding EEG reactions comprised discrete individual spectral peaks both in traditional (1-30 Hz) and gamma (30-80 Hz) ranges and higher-frequency components (80-200 Hz) as well. In some cases, the higher-frequency components (80-200 Hz) were most pronounced.     

Neuronal responses in the cat substantia innominata during instrumental conditioned reflex

Neuronal spike activity in the substantia innominata was investigated when establishing the instrumental conditioned reflex of lever-pressing with food reinforcement during chronic experiments on cats. Spike activity changed in 44.3% of neurons during this process; 24.3% responded directly to conditioned acoustic stimulation. Reactions associated with conditioned reflex movement were less pronounced. Response of peak intensity and duration was observed during food reinforcement, when the reaction occasionally occurred 500 msec in advance of the reinforcement provided. Involvement of cholinergic substantia innominata neurons in reinforcement is thought to be responsible for the persistence of residual effects in neocortical neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 796–804, November–December, 1989.     

Neuronal correlates of an alimentary instrumental conditioned reflex in rats

Elaboration of an instrumental reaction of getting the food from a narrow tube with a defnite forepaw (handedness) brings about a distinct re-distribution of cellular activity in the motor cortex and in the caudate nucleus, contralateral to the instrumental paw. The changes were observed at a 250 msec. interval before and 512 msec. interval after the beginning of the movement. Two types of cellular discharge changes were recorded: phasic and tonic. The phasic reactions (both inhibitory and activating) were grouped around the beginning of movement, with an average duration of about 100 msec. The tonic reactions lasted a few hundred milliseconds.     

Excitability cycles of direct cortical responses during elaboration of conditioned defense reflexes in dogs]

Direct cortical responses (DCRs) to paired stimuli were studied in chronic experiments in dogs during elaboration of classical and instrumental defensive conditioned reflexes. The DCRs were recorded with 20 to 250 ms intervals between stimuli. Paired and single electrical stimulations of the middle suprasylvian gyrus given with a frequency of one per second were used as conditioned stimuli and were reinforced in a similar way. During electrical cutaneous stimulation of the dog's paw and to an even greater extent during isolated action of the conditioned stimulus the initial negativity of the testing DCR became shorter and the degree of its depression diminished. In the case of a following period of facilitation, its degree became greater. It was higher at a distance of 4 to 5 mm from the point of stimulation than at a distance of 2 to 3 mm. During isolated action of the conditioned stimulus, the degree of facilitation was higher than at the period of the possible action of the unconditioned stimulus. The greatest shorterning of the DCR excitability cycle was observed immediately before and during the conditioned lifting of the dog's paw. Excitability cycles of DCR, and possibly of other evoked potentials as well, are a more sensitive indicator of the function state of the cerebral cortex than responses to single stimuli. For this reason it appears promising to use them in studying conditioned reflexes.     

Responses of limbic cortical neurons during instrumental conditioned reflexes in cats

Unit activity in cortical areas 24 and 32 was studied during conditioned placing reflex formation in cats. Neuronal responses in the limbic cortex of trained animals correlated with acoustic stimulation, the motor response, and also with the presentation of food reinforcement. In untrained animals 16% of neurons responded to acoustic stimulation. After training the number of neurons responding to sound in area 32 increased to 51.3%. Of the total number of neurons, 34.6% responded by initial excitation and 26.7% by inhibition of spike activity. The latent period of these responses was about 50 msec and their duration up to 200 msec. Similar but weaker responses were observed in area 24. Short-latency activation responses to conditioned and differential stimulation were similar in character. It is suggested that after training processes taking place in the limbic cortex may contribute to better perception of both conditioned and differential acoustic stimuli, irrespective of their functional significance.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 201–208, March–April, 1984.     

Activity of neurons in the pedunculopontine nucleus during defensive instrumental conditioning

The activity of 109 neurons in the compact and diffuse parts of the pedunculopontine tegmental nucleus (PPTg) was recorded in freely moving rabbits during the acquisition and actualization of the defensive instrumental conditioned reflex. It was found that 47% of the recorded neurons responded to a conditioned stimulus (CS). This finding suggests the involvement of the PPTg in the instrumental conditioning. A significant prevalence of the excitatory conditioned responses to the CS suggests the predominantly activating influence of the PPTg on its projection structures during conditioning. The neuronal responses to the CS were classified into several basic patterns reflecting stimulus effects, the structure of the behavioral act, and the nature of the reinforcement. They indicated the involvement of the PPTg in attention, motor learning, and reinforcement. A significant decrease in the reactivity of the CS of the PPTg neurons as a result of learning specialization was shown. The revealed differences in the associative and reactive properties (with respect to CS) between the neurons of the compact and diffuse PPTg parts testify to the functional heterogeneity of this structure and suggest the leading role of the cholinergic compact part of the PPTg in the instrumental defensive conditioning. Thus, the obtained evidence suggests the involvement of the PPTg in the mechanisms of attention and acquisition of the active defensive motor conditioning.     

Generalization of an instrumental defensive conditioned reflex elaborated to electric stimulation of the hypothalamus in dogs

Generalization of defensive conditioned reflexes elaborated to electrical stimulation of the lateral hypothalamus (LH) was studied in four dogs with electrodes implanted in various structures of the limbic system. Electrocutaneous stimulation was switched off when the dog lifted the foreleg to a definite level. Generalization of the conditioned reflex was manifested in different degrees when testing different formations of the limbic system, or testing one and the same structure, but at different stages of conditioning. Two types of generalization were found: the first one--a well pronounced motor reaction, by its latency, level and duration of lifting the foreleg similar to movements appearing in response to the conditioned stimulus; and the second one--low amplitude or short-term movements differing from conditioned ones. The first type of generalization was observed in response to stimulation of LH, contralateral to the point of signal stimulation, of the ventromedial hypothalamic nucleus, the mammillary bodies and the basal, lateral and to a lesser degree, the central nucleus of the amygdaloid complex; the second type--in response to stimulation of the ventral hippocampus, the medial and lateral septum nuclei.     

The role of signal and motivational links of a conditioned reflex in the initiation of instrumental movements in dogs

Alimentary instrumental conditioned reflex (CR) was elaborated in dogs to light flashes (I series), electrostimulation (ES) of the hippocampus (II series) and the hypothalamus (III series). Nonreinforced ES of the hypothalamus, amygdala, hippocampus and septum reproduced pressings on the pedal to the least extent in the I series (17-40% of trials), increasing in the II-nd one up to 40-87% during stimulation of the lateral hypothalamus, medial amygdala and contralateral hippocampus. In the III-rd series the number of pressings increased statistically significantly in comparison with the I-st series for most structures. Probably, besides the artificial increase of motivation during ES of the limbic structures which took place in all series, in the II-nd and III-rd series significance for movement reproduction was acquired by CR generalization appearing due to close interconnection of the structures. In this phenomenon connections (evaluated by the EPs) from the tested structures to the initially signal one are important.     

Amphetamine effects on unconditional and conditional instrumental responses with alimentary and social rewards in dogs

The effect of amphetamine dose (0.5 mg per 1 kg) on conditional and unconditional responses based on alimentary and social motivation was investigated in two groups of dogs. Amphetamine resulted in a significant decrease of conditional instrumental responses (CRs) in both groups but did not attenuate significantly the dogs' need for food or petting. On the contrary, the drug drastically increased the dogs' need for petting, and its anorectic effect was mild. The deteriorating effect of amphetamine on mnemonic processes and its facilitatory effect on behaviors directed to get more than the usual amount of pleasant tactile stimulation might underlie the behavioral changes described in this study.