Effects of experience on striatal sensory responses

Parallel associative processing in the dorsal striatum: segregation of stimulus-response and cognitive control subregions

Although evidence suggests that the dorsal striatum contributes to multiple learning and memory functions, there nevertheless remains considerable disagreement on the specific associative roles of different neuroanatomical subregions. We review evidence indicating that the dorsolateral striatum (DLS) is a substrate for stimulus-response habit formation - incremental strengthening of simple S-R bonds - via input from sensorimotor neocortex while the dorsomedial striatum (DMS) contributes to behavioral flexibility - the cognitive control of behavior - via prefrontal and limbic circuits engaged in relational and spatial information processing. The parallel circuits through dorsal striatum interact with incentive/affective motivational processing in the ventral striatum and portions of the prefrontal cortex leading to overt responding under specific testing conditions. Converging evidence obtained through a detailed task analysis and neurobehavioral assessment is beginning to illuminate striatal subregional interactions and relations to the rest of the mammalian brain.

Studies of the functional characteristics of central neurons of the brain in a behavioral experiment

The activity of central integrative brain neurons is associated with the overall assessment of functionally diverse signals of different sensory modalities which converge on these neurons via parallel inputs. Processing this information, these neurons take part in organizing the animal's various actions and in the mechanisms involved in switching from one action to another. Therefore, understanding of the functional characteristics of central brain neurons requires studies in which the dynamics of neuron activity are recorded continuously throughout a sequence of actions performed by an animal. Traditional methods of analyzing neuron activity, such as the construction of post- and peristimulus histograms and cross-correlation analysis, are inadequate for this purpose. These methods allow analysis to be applied to neuron spike activity only around each synchronization point Their use for studies of a developed program of animal actions unavoidably leads to a set of separate histograms providing no information on the dynamics of neuron activity corresponding to continuous behavior. A complex approach to studying the neuronal correlates of behavior is suggested, designed to overcome these difficulties. The method is based on the use of a developed behavioral program with recording of several neurons in parallel, with analysis of neuron activity using a relative time scale based on the duration of each sequentially performed action. Non-traditional methods of processing neuron spike activity were developed for analysis of the resulting data, including construction of relative histograms and multidimensional statistics methods. These approaches allowed us to study the dynamics of neuron activity continuously through all the stages of performance of a behavioral program and obtain data on the involvement of each group of those neurons which were studied in functionally different actions. This methodology was tested using studies of the functional characteristics of striatum neurons in monkeys. Comparable data were obtained on the individual responses of neurons and on the dynamics of their activity at different stages of the animals' performance of a multicomponent behavioral program. This revealed the lack of functional specialization in striatum neurons and different patterns of their involvement in motor and cognitive functions.

Response properties of neurons in the caudate-putamen and globus pallidus to noxious and non-noxious thermal stimulation in anesthetized rats

To investigate the possible mechanisms by which neurons in the caudate-putamen (CPu) and globus pallidus (GP) participate in pain and nociception, the present study characterized the response properties of CPu and GP neurons to non-noxious and noxious thermal stimuli in anesthetized rats. Nociceptive CPu and GP neurons were capable of encoding noxious thermal stimuli and 79% of these thermally responsive neurons also responded to noxious mechanical stimuli. Thermally responsive neurons were activated during the phasic rise and fall of the thermal shift in addition to the plateau temperature. The ability of CPu and GP neurons to encode noxious thermal stimulation intensity and respond during the dynamic phase of the stimulus suggests that these neurons may contribute to the behavioral response to minimize bodily harm.

Involvement of striatum (putamen) neurons in motor and nonmotor behavior fragments in monkeys

Putamen neuron spike activity associated with motor and nonmotor functions was studied in monkeys trained to behavioral programs consisting of a series of sequential actions. In general, each putamen neuron was activated during particular behavior fragments. The association of each individual neostriatal neuron with particular behavioral fragments was not constant. When the animal performed a different version of the same program (using different conditioned signals, right- or left-sided tasks, correct or erroneous performance), the neuron could lose its association with the animal's action and become involved in a different action to which it had previously produced no response. Thus, putamen neurons could demonstrate different functional modalities in different versions of the same actions. The use of additional versions of the given program always led to increases in the numbers of behavior fragments during which there were changes in the spike activity of the neurons of interest. This effect was significantly stronger in motor fragments of the program than in nonmotor fragments. These results show that putamen neurons do not have any defined specialization and have different functional modalities when the animal performs different versions of the same action. The nature of putamen neuron involvement in sensory-cognitive processes was more stable than in the organization of motor responses.