Classical Conditioning Procedure Research Articles

Role of the dopamine D3 receptor in reactivity to cocaine-associated cues in mice.

Environmental stimuli previously associated with drug effects can acquire secondary reinforcing properties, able to maintain drug-seeking behaviour or induce relapse. We have used a classical Pavlovian conditioning procedure to assess the role of the dopamine D3 receptor (D3R) in the expression of drug-conditioned responses. Mice repeatedly receiving cocaine in a particular environment distinct from home-cages displayed hyperlocomotion after subsequent exposure to the drug-paired environment. Cocaine-conditioned hyperactivity was inhibited by BP 897 or SB-277011-A, D3R-selective partial agonist and antagonist, respectively. D3R gene-targeted mice showed a trend towards an increase in cocaine cue-conditioned hyperactivity. BP 897 had no effect on reactivity to neutral or aversive cues. Cocaine-conditioned mice had increased levels of D3R mRNA and binding in the nucleus accumbens (NAc), and transcripts of brain-derived neurotrophic factor (BDNF), a factor controlling D3R expression, in the ventral tegmental area (VTA). Cocaine had no effects on D3R or BDNF genes when administered in home-cages. Cocaine cue-conditioned c-fos expression was found in cortical areas, notably in the somatosensory cortex, where it was inhibited by BP 897, and in several regions belonging or linked to the limbic system. In conditioned mice, BP 897 inhibited c-fos expression in VTA and activated it in amygdala. These results demonstrate a modulation of reactivity to cocaine cues by the D3R, the expression of which is elevated in the NAc by the repeated association of drug effects with a particular context, through a BDNF-dependent mechanism. D3R-selective partial agonist or antagonist inhibit cocaine cue-conditioned activity possibly by normalizing exacerbated D3R function in the NAc, but our results also point to a possible participation of a pathway involving the VTA, amygdala and somatosensory cortex.

Neural organization of eyelid responses.

A blink is a fast narrowing of the palpebral fissure, involving the activity of the orbicularis oculi muscle and, in those species with a nictitating membrane, of the retractor bulbi motor system and most extraocular eye muscles. Reflex blinks can be triggered by stimuli of different sensory modalities (trigeminal, visual, acoustic, and vestibular). Blinks are not exclusively related to corneal protection and wetting, but are also associated with some stages of visual processing and with the complex motor displays involved in the expression of emotional states. Lid movements also accompany eye displacements, as during vertical eye saccades and fixations. Moreover, eyelid movements can be easily evoked using classical conditioning procedures. 1‐9 Because of the technical facilities available for the quantitative evoking and recording of nictitating membrane and/or eyelid movements, 3 this motor system has become an excellent experimental model for the study of learned motor responses. In addition, available relevant information on this motor system can be used as a very useful tool for the understanding of the different pathologies related to facial kinematics and expression in humans.

Auditory frequency discrimination in the squirrel monkey.

Four squirrel monkeys (Saimiri sciureus) were tested for their frequency discrimination capacity using an eyeblink classical conditioning procedure, with air puff against the eye as unconditioned stimulus and 600-ms pure tones as conditioned stimuli. Absolute frequency difference thresholds showed a minimum (20-41 Hz, mean 30 Hz) at 4,000-8,000 Hz and increased towards higher as well as lower frequencies (70-90 Hz, mean 80 Hz at 300 Hz; 44-120 Hz, mean 82 Hz at 16,000 Hz). Relative frequency difference thresholds increased from higher to lower frequencies, with values as low as 0.3-0.8% (mean 0.5%) at 16,000 Hz and as large as 24-30% (mean 27%) at 300 Hz. The squirrel monkey's frequency discrimination function thus shows a severe deviation from Weber's law. The frequency difference thresholds are comparable to human's in the 4,000-8,000 Hz range, but are 65-80 times higher in the 500- to 300-Hz range. Individuals with high auditory thresholds do not necessarily also have high frequency difference thresholds.

Training Captive‐Bred or Translocated Animals to Avoid Predators

Abstract:Animal reintroductions and translocations are potentially important interventions to save species from extinction, but most are unsuccessful. Mortality due to predation is a principal cause of failure. Animals that have been isolated from predators, either throughout their lifetime or over evolutionary time, may no longer express appropriate antipredator behavior. For this reason, conservation biologists are beginning to include antipredator training in pre‐release preparation procedures. We describe the evolutionary and ontogenetic circumstances under which antipredator behavior may degenerate or be lost, and we use principles from learning theory to predict which elements can be enhanced or recovered by training. The empirical literature demonstrates that training can improve antipredator skills, but the effectiveness of such interventions is influenced by a number of constraints. We predict that it will be easier to teach animals to cope with predators if they have experienced ontogenetic isolation than if they have undergone evolutionary isolation. Similarly, animals should learn more easily if they have been evolutionarily isolated from some rather than all predators. Training to a novel predator may be more successful if a species has effective responses to similar predators. In contrast, it may be difficult to teach proper avoidance behavior, or to introduce specialized predator‐specific responses, if appropriate motor patterns are not already present. We conclude that pre‐release training has the potential to enhance the expression of preexisting antipredator behavior. Potential training techniques involve classical conditioning procedures in which animals learn that model predators are predictors of aversive events. However, wildlife managers should be aware that problems, such as the emergence of inappropriate responses, may arise during such training.

Emergence of Conditional Stimulus Relations and Transfer of Respondent Eliciting Functions Among Compound Stimuli

Previous research has demonstrated that conditioned elicitation functions can transfer via stimulus equivalence classes. However, thus far investigations in this area have been limited to stimulus equivalence classes involving single element stimuli. This study attempted to demonstrate the transfer of eliciting functions via emergent relations involving compound stimuli. Eight college students participated in this study. Six of these participated in all experimental procedures, while the remaining two served as controls and did not receive some phases of the experiment. The experimental participants were first taught nine conditional relations of compound stimuli and unitary stimuli (AC-B & BC-A) using match-to-sample training. They were then tested for the emergence of untrained relations involving different combinations of the previously learne9 compound-single element relations and compound-compound relations (AC-AC or AB-AB or BC-BC). A classical conditioning procedure was then performed in which one compound stimulus from one class was paired with mild electric shock (1.0-2.0 mA) while two other compounds from two different classes were presented in the absence of shock. Participants were then presented with other compounds from the appropriate classes to assess whether the eliciting function had transferred to stimuli which were members of the same class as the originally conditioned stimulus. The control participants received the same procedures except for the initial conditional discrimination training of the compound-single relations and the testing for the emergence of compound-single relations. Four of thoe six experimental participants demonstrated transfer of the eliciting function. An analysis of the performance of both of the individuals who failed to demonstrate the transfer revealed that they may have failed to ° maintain the classes throughout the experiment. One participant discontinued the experiment before further procedures

Emotional modulation of attention orienting: A classical conditioning study

Emotional modulation of attention shifting was investigated in Posner’s (1980) spatial orienting task by conditioning the attention cue to an aversive white noise. Prior to the attention task, the Conditioning group received a 90dB white noise unconditioned stimulus (UCS) contingent upon the frame‐lit rectangle attention cue, while the Control group received non‐contingent presentations. The Conditioning group evidenced greater skin conductance responses to the frame‐lit rectangle in the conditioning phase, reflecting an electrodermal conditioned response. In the attention phase, the frame‐lit rectangle served as the attention cue in the spatial orienting task. The Conditioning group showed equally fast reaction times (RTs) to targets presented outside the location of the cue as to targets at the same location as the cue, reflecting elimination of the cognitive cost usually involved in shifting attention. The Control group evidenced the regular cost of shifting attention away from the location of the cue. The Conditioning group also evidenced a larger N1‐component with a parietal distribution of the event‐related brain potentials to the cue and a larger N1‐component at the frontal regions to targets presented outside the cued location. This suggests that both visual orienting to the cue and attention shifting from cue to target on invalid trials were amplified by the emotional salience attached to the cue through the classical conditioning procedure.

Separate Effects of a Classical Conditioning Procedure on Respiratory Pumping, Swimming, and Inking inAplysia fasciata

We examined whether swimming and inking, two defensive responses in Aplysia fasciata, are facilitated by a classical conditioning procedure that has been shown to facilitate a third defensive response, respiratory pumping. Training consisted of pairing a head shock (UCS) with a modified seawater (85%, 120%, or pH 7.0 seawater--CSs). Animals were tested by re-exposing them to the same altered seawater 1 hr after the training. For all three altered seawaters, only respiratory pumping is specifically increased by conditioning. Swimming is sensitized by shock, and inking is unaffected by training, indicating that the conditioning procedure is likely to affect a neural site that differentially controls respiratory pumping. Additional observations also indicate that the three defensive responses are differentially regulated. First, different noxious stimuli preferentially elicit different defensive responses. Second, the three defensive responses are differentially affected by shock. Inking is elicited only immediately following shock, whereas swimming and respiratory pumping are facilitated for a period of time following the shock. Third, swimming and respiratory pumping are differentially affected by noxious stimuli that are delivered in open versus closed environments. These data confirm that neural pathways exist that allow Aplysia to modulate separately each of the three defensive behaviors that were examined.

Are separate theories of conditioning and timing necessary?

Conditioning and timing studies have evolved under separate traditions, which is exemplified in both traditional theories (e.g. the Rescorla–Wagner model of conditioning vs. Scalar Timing Theory) and in a dual process model (Gibbon, J., Balsam, P., 1981. In: Autoshaping and Conditioning Theory. Academic Press, New York.). Other lines of theoretical development in both timing and conditioning fields have resulted in the emergence of ‘hybrid’ theories in which conditioning and timing processes are integrated. Simulations were conducted with a recent hybrid theory of timing (Machado, A., 1997. Psychol. Rev. 104, 241–265). The simulations were of classical conditioning procedures in which the local or global predictability of food was varied by manipulating the variability of the CS–US relationship, variability of the CS duration, and variability of the intertrial interval. The hybrid model provided good qualitative fits to indices of conditioning (discrimination ratios) and timing (local rates of responding), indicating that it may be possible to model both conditioning and timing results with a single process in which an internal representation of time and a strength of association are integrated. However, the failure of the model to provide good quantitative fits of the data indicates the need for a consideration of alternative perceptual representations of time and/or principles of association within the framework of the hybrid model.

Dissociation of consummatory and vocal components of feeding in squirrel monkeys treated with benzodiazepines and alcohol.

The primary aim of the current experiments was to develop methods that engender vocalizations associated with positive social situations comprising affiliative behavior and feeding that could be quantified under controlled laboratory conditions and were sensitive to anxiolytic drugs. Classical conditioning procedures were used to elicit vocalizations during presentation of stimulus lights (i.e., CS condition) previously paired with either preferred foods (e.g., grapes, peanuts, bananas) or standard foods (e.g., monkey chow) as well as during presentation of both food types (i.e., UCS condition). When compared to the period before stimulus light presentation (i.e., Pre-CS condition), the rate, duration and number of elemental units of food-related "twitter" vocalizations were increased during the CS conditions regardless of food type. Monkeys spent significantly more time oriented toward the food box during the light stimulus that preceded preferred food than for the light stimulus that preceded standard food. However, twitter vocalizations were higher for standard food regardless of the stimulus conditions (i.e., Pre-CS, CS and UCS). Administration of the benzodiazepine full agonist chlordiazepoxide (CDP, 1-10 mg/kg), the partial agonist bretazenil (BRZ, 1-10 mg/kg), the antagonist flumazenil (FLZ, 1-10 mg/kg) and ethyl alcohol (EtOH, 0.1-1.0 g/kg) differentially altered vocalizations. Although CDP and BRZ increased feeding of standard food, twitters were reduced across stimulus conditions. CDP and BRZ did not alter other social contact calls (i.e., "peeps"). FLZ also reduced twitters without altering peeps, but did not increase feeding. In contrast, EtOH did not increase feeding or peeps, but did increase food-related twitters. These results indicate that there is a dissociation between food-related behaviors, such as food consumption and orientation towards the food source, and vocal behaviors associated with group communication during feeding.

Changes in neurotransmitter release in the main olfactory bulb following an olfactory conditioning procedure in mice

Olfactory learning is associated with substantial neural changes at the level of the accessory and main olfactory bulb, during both pheromonal learning in mated mice and lamb odour recognition in post partum sheep. These forms of learning occur during “sensitive periods” and an important question is whether similar neural changes occur in the olfactory bulb at other times. We used a classical conditioning procedure to establish an olfactory discrimination in adult mice and then measured changes in neurotransmitter levels in the main olfactory bulb in response to the presentation of the conditioned odours. Presentation of the conditioned, but not the non-conditioned, odour resulted in significant increases in the levels of certain transmitters, including glutamate from the mitral/tufted cells, GABA from the granule and periglomerular cells and noradrenaline from the centrifugal projection from the locus coeruleus. Overall, there was a decrease in the ratio of excitatory to inhibitory neurotransmitters in the olfactory bulb in response to the conditioned, but not the non-conditioned odour. Moreover, the magnitude of the decrease in this ratio was correlated with the level of behavioural response to the conditioned odour. These findings support the hypothesis that changes in the gain of the reciprocal synapses between mitral/tufted neurons and their inhibitory interneurons are a general feature of olfactory learning.

The effect of frustrative nonreward on vocalisations and behaviour in the laying hen, Gallus gallus domesticus

Laying hens are thought to express an expectation of a rewarding event through a specific vocalisation, the gakel-call. It has been suggested that the gakel-call is related to frustration, i.e. the thwarting of behaviour. We investigated if frustrative nonreward (nonreinforcement in a situation that previously was consistently reinforcing) in laying hens is expressed through this gakel-call. Twenty hens of two commercial strains, ten ISA White Leghorn and ten ISA Brown Warren were subjected to a classical conditioning procedure. After 23 h of food-deprivation they were trained, in automated Skinnerboxes, to use red lights as a signal (unconditioned stimulus) for a food reward. After this the hens of each strain were equally divided into two groups of five. They were subjected to a control session (light as conditioned stimulus followed by food reward) and to a frustration session (conditioned stimulus followed by nonreward). Both during the frustration and control session behaviour and vocalisations were recorded. In the White Leghorn strain high levels of alarm-calls are found as indicators of anxiety. In the Brown Warren strain more gakel-calls and an increased locomotor activity are found after frustrative nonreward. In conclusion, both findings suggest that vocalisations could serve as indicators of a laying hen's welfare.

Multiple Sites of Associative Odor Learning as Revealed by Local Brain Microinjections of Octopamine in Honeybees

In a classical conditioning procedure, honeybees associate an odor with sucrose resulting in the capacity of the odor to evoke an appetitive response, the extension of the proboscis (PER). Here, we study the effects of pairing an odor with injections of octopamine (OA) as a substitute for sucrose into three putative brain sites of odor/sucrose convergence. OA injected into the mushroom body (MB) calyces or the antennal lobe but not the lateral protocerebral lobe produces a lasting, pairing-specific enhancement of PER. During pairings, OA injected into the MB calyces results in an additional pairing-specific effect, because it does not lead to an acquisition but a consolidation after conditioning. These results suggest that the neuromodulator OA has the capacity of inducing associative learning in an insect brain. Moreover, they suggest the antennal lobes and the calyces as at least partially independent sites of associating odors that may contribute differently to learning and memory consolidation.

The Persistence of Classically Conditioned Brand Attitudes

The researchers investigated the long-term effects of classically conditioned attitudes toward a brand. In two experiments, subjects were exposed to classical conditioning procedures in which favorable images were paired with a fictitious brand of mouthwash. Study 1, a within-subjects design, examined attitudes of a single subject pool immediately after exposure, after a one-week delay, and after a three-week delay. In study 2, the same methods and procedures were used to condition favorable responses to the test brand, but a between-subjects design was used to control for possible measurement effects. Measurements were taken immediately after exposure to conditioning trials for one group of subjects and three weeks after exposure to the trials for a second group. Results from both studies support the hypothesis that attitudes formulated through classical conditioning are enduring.

Extinction of enhanced latent inhibition

Hungry rats were used in a classical conditioning procedure in which visual stimuli were paired with food. Conditions in which nonreinforced exposure to a nontarget stimulus was followed by exposure to a simultaneous compound nontarget/target stimulus (a blocking procedure) resulted in enhanced latent inhibition to the target relative to exposure to the nontarget, followed by exposure to the target stimulus alone. A third phase of nonreinforced exposure training, in which the target was exposed alone following the compound, reduced levels of latent inhibition relative to results obtained with the blocking procedure. Experiments also suggested that this was not the result of restoration of associability by the omission of an expected presentation of the nontarget stimulus in the final preexposure phase. These results suggest that enhanced latent inhibition is due to summation of a direct-target-no-event association and a second-order association of these elements via target-nontarget and nontarget-no-event association. Exposure to the target after compound exposure extinguished the target-nontarget association and reduced the sources of no-event learning for the target.

The transfer of avoidance evoking functions through stimulus equivalence classes

Recent research in the area of stimulus equivalence suggests that transfer of function via members of stimulus equivalence classes may have relevance to human emotional responding and the development and generalization of certain psychological disorders. This study investigated the transfer of avoidance evoking functions through equivalence classes. Eight subjects were trained in the necessary relations for two-four member stimulus equivalence classes to emerge. Next, using an on-baseline classical conditioning procedure, one member of one class was paired with shock while one member of the other class was presented without shock. Then, while subjects engaged a key-press task, a differential, signalled avoidance task was introduced wherein shock was avoided if a response occurred to the stimulus previously associated with shock. The remaining stimuli from both classes were then presented. The behavior of all eight subjects showed the differential transfer of the avoidance evoking function. The clinical and theoretical implications of the results are discussed.

Discrimination of oilseed rape volatiles by the honeybee: combined chemical and biological approaches

AbstractHoneybees (Apis mellifera L.) were individually subjected to a classical conditioning procedure in order to obtain an olfactory conditioned proboscis extension response. To relate the behavioural response directly to antennal detection abilities, a technique was developped for coupling proboscis extension responses and electroantennogram recordings, with the stimulation being provided by the effluent of a gas chromatograph (GC). Bees were conditioned with a six‐component mixture being part of oilseed rape (Brassica napus L.) floral volatiles, and tested with the individual components separated by GC. Responses of the conditioned bees were compared to those of unconditioned bees. No behavioural response was obtained in the control group, neither to the individual components nor to the mixture. Conditioning induced behavioural responses for three components, and an increase of electroantennogram responses for all components. A second experiment was conducted with an air entrainment extract of oilseed rape flower volatiles. Behavioural responses of conditioned and unconditioned bees were recorded. Responses obtained from conditioned bees tested with the air entrainment extract showed six groups of behaviourally active GC peaks. Unconditioned bees showed the same pattern of responses but at a lower level. The coupled technique described here appears to be a reliable tool for locating active components in a synthetic as well as in a natural mixture of floral volatiles. The effects of conditioning on odour discrimination and on its sensory correlates are discussed.

The Effect of Loss of Predictability and Controllability of Reward During Frustration On Behaviour in Two Strains of Laying Hens, Gallus Gallus Domesticus

In order to keep a high level of welfare an animal has to interact with the environment. Predictability and controllability of environmental stimuli seem to be of major importance. Loss of predictability and loss of controllability have a detrimental effect on animals. We hypothesised that both loss of predictability and loss of controllability would, among other behavioural effects of frustration, lead to an increase in the number of gakel-calls in laying hens. The gakel-call, expressed during the thwarting of behaviour, presumably is an indicator of frustration in laying hens. Predictability of reward was offered by a classical conditioning procedure, controllability of reward by operant conditioning. Assuming that controllability is predictability plus added control we also hypothesised that loss of controllability would lead to higher levels of gakel-calls than loss of predictability. Twenty hens of two commercial strains of laying hens, 10 ISA Brown Warrens and 10 ISA White Leghorns, were used. These strains of hens are known to differ in their reaction to frustration. They were subjected to frustration during a classical and an operant conditioning situation in a counterbalanced design. We found that in both conditioning situations the hens gave more gakel-calls in the frustration treatment than in the control treatment. No difference in levels of gakel-calls during frustration between classical and operant conditioning was found. Both loss of predictability and loss of controllability seem to impair a laying hen's welfare. The results suggest that the strains differ in behavioural strategy during frustration. When using the gakel-call as measure for welfare this difference in behavioural strategy should be taken into account.

Dendritic excitability microzones and occluded long-term depression after classical conditioning of the rabbit's nictitating membrane response.

We made intradendritic recordings in Purkinje cells (n = 164) from parasaggital slices of cerebellar lobule HVI obtained from rabbits given paired presentations of tone and periorbital electrical stimulation (classical conditioning, n = 27) or explicitly unpaired presentations of tone and periorbital stimulation (control, n = 16). Purkinje cell dendritic membrane excitability, assessed by the current required to elicit local dendritic calcium spikes, increased significantly in slices from animals that received classical conditioning. In contrast, membrane potential, input resistance, and amplitude of somatic and dendritic spikes were not different in slices from animals given paired or explicitly unpaired stimulus presentations. The location of cells with low thresholds for local dendritic calcium spikes suggested that there are specific sites for learning-related changes within lobule HVI. These areas may correspond to learning "microzones" and are consistent with locations of learning-related in vivo changes in Purkinje cell activity. Application of 4-aminopyridine, an antagonist of the rapidly inactivating potassium current IA, reduced the threshold for dendritic spikes in slices from naive animals to levels found in slices from trained animals. In cells where thresholds for eliciting parallel fiber-stimulated Purkinje cell excitatory postsynaptic potentials (EPSPs) were measured, levels of parallel fiber stimulation required to elicit a 6-mV EPSP as well as a 4-mV EPSP (n = 30) and a Purkinje cell spike (n = 56) were found to be significantly lower in slices from paired animals than unpaired controls. A classical conditioning procedure was simulated in slices of lobule HVI by pairing a brief, high-frequency train of parallel fiber stimulation (8 pulses, 100 Hz) with a brief, lower frequency train of climbing fiber stimulation (3 pulses, 20 Hz) to the same Purkinje cell. Following paired stimulation of the parallel and climbing fibers, Purkinje cell EPSPs underwent a long-term (> 20 min) reduction in peak amplitude (-24%) in cells (n = 12) from animals given unpaired stimulus presentations but to a far less extent (-9%) in cells (n = 20) from animals given in vivo paired training. Whereas 92% of cells from unpaired animals showed pairing-specific depression, 50% of cells from paired animals showed no depression and in several cases showed potentiation. Our data establish that there are localized learning-specific changes in membrane and synaptic excitability of Purkinje cells in rabbit lobule HVI that can be detected in slices 24 h after classical conditioning. Long-term changes within Purkinje cells that effect this enhanced excitability may occlude pairing-specific long-term depression.

Conditioned response timing and integration in the cerebellum.

Classical conditioning procedures instill knowledge about the temporal relationships between events. The unconditioned stimulus (US) is the event to be timed. The conditioned response (CR) is viewed as a prediction of the imminence of the US. Knowledge of the elapsed time between conditioned stimuli (CSs) and US delivery is expressed in the topological features of the CR. The peak amplitude of the CR coincides with the timing of the US. A simple connectionist network based on Sutton and Barto's Time Derivative (TD) Model of Pavlovian Reinforcement provides a mechanism that can account for and simulate CR timing in a variety of protocols. This article describes extensions of the model to predictive timing under temporal uncertainty. The model is expressed in terms of equations that operate in real time according to a competitive learning rule. The unfolding of time from the onsets and offsets of events such as CSs is represented by the propagation of activity along a sequence of time-tagged elements. The model can be aligned with anatomical circuits of the cerebellum and brain stem that are essential for learning and performance of conditioned eye-blink responses.

Injury- and use-related plasticity in the primary sensory cortex of adult mammals: possible relationship to perceptual learning.

1. Restricted cochlear lesions in adult animals result in a reorganization of auditory cortex such that the cortical region deprived of its normal input by the lesion is occupied by expanded representations of adjacent cochlear loci (and thus of the frequencies represented at those loci). Analogous injury-induced reorganization is seen in somatosensory, visual and motor cortices of adult animals after restricted peripheral lesions. 2. Rather than constituting a central compensation for the peripheral loss, such reorganization appears to be an extreme form of changes in cortical organization that occur as a consequence of altered patterns of input such as arise from differential use of restricted regions of receptor surfaces ('use-related' reorganization). Thus, the frequency organization of auditory cortex is modified in animals trained to perform a frequency discrimination task and analogous changes in the frequency selectivity of cortical neurons are produced by classical conditioning procedures. 3. Recent evidence from the visual system suggests that changes similar to those involved in injury- and use-related cortical reorganization may underlie some forms of what has been called 'perceptual learning', the improvement in sensory/ perceptual discriminative performance with practice. Some forms of such learning are highly specific to the particular stimuli used in training (i.e. do not generalize to other stimuli), suggesting that the improved performance reflects a change in neural circuitry at a relatively early level of sensory processing. The limited available evidence supports the occurrence of such learning in the auditory system. 4. Recent studies using functional imaging and related techniques indicate that injury- and use-related reorganization occurs in human sensory and motor cortex.