Class I histone deacetylases inhibition reverses memory impairment induced by acute stress in mice.

While chronic stress induces learning and memory impairments, acute stress may facilitate or prevent memory consolidation depending on whether it occurs during the learning event or before it, respectively. On the other hand, it has been shown that histone acetylation regulates long-term memory formation. This study aimed to evaluate the effect of two inhibitors of class I histone deacetylases (HDACs), 4-phenylbutyrate (PB) and IN14 (100 mg/kg/day, ip for 2 days), on memory performance in mice exposed to a single 15-min forced swimming stress session. Plasma corticosterone levels were determined 30 minutes after acute swim stress in one group of mice. In another experimental series, independent groups of mice were trained in one of three different memory tasks: Object recognition test, Elevated T maze, and Buried food location test. Subsequently, the hippocampi were removed to perform ELISA assays for histone deacetylase 2 (HDAC2) expression. Acute stress induced an increase in plasma corticosterone levels, as well as hippocampal HDAC2 content, along with an impaired performance in memory tests. Moreover, PB and IN14 treatment prevented memory loss in stressed mice. These findings suggest that HDAC2 is involved in acute stress-induced cognitive impairment. None of the drugs improved memory in non-stressed animals, indicating that HDACs inhibitors are not cognitive boosters, but rather potentially useful drugs for mitigating memory deficits.

Inhibition of corticosterone synthesis impairs cued water maze consolidation, but it does not affect the expression of BDNF, CK2 and SGK1 genes in dorsal striatum.

Corticosterone (CORT) release during learning experiences is associated with strong memories and activity of the glucocorticoid receptor. It has been shown that lesions of the dorsal striatum (DS) of rats trained in the cued version of the Morris water maze impair memory, and that local injection of CORT improves its performance, suggesting that DS activity is involved in procedural memory which may be modulated by CORT. We trained rats in cued Morris water maze and analyzed the effect of CORT synthesis inhibition on performance, CORT levels, expression of plasticity-involved genes, such as the brain derived neurotrophic factor (BDNF), casein kinase 2 (CK2), and the serum/glucocorticoid regulated kinase 1 (SGK1), as well as the presence of phosphorylated nuclear glucocorticoid receptor in serine 232 (pGR-S232) in the DS. The inhibition of CORT synthesis by metyrapone reduced CORT levels in plasma, prevented its increment in DS and impaired the performance of cued water maze. Additionally, there was an increase of CK2 and SGK1 mRNAs expression in trained subjects, which was unrelated to CORT levels. Finally, we did not observe changes in nuclear pGR-S232 in any condition. Our findings agree with evidence demonstrating that decreasing CORT levels hinders acquisition and consolidation of the spatial version of the Morris water maze; these novel findings broaden our knowledge about the involvement of the DS in the mechanisms underlying procedural memory.

Intense inhibitory avoidance training increases nuclear-phosphorylated glucocorticoid receptors in neurons of CA1 of hippocampus and ventral caudate putamen.

Corticosterone (CORT), the principal glucocorticoid in rodents, is released after stressful experiences such as training with high foot-shock intensities in the inhibitory avoidance task (IA). CORT reaches the glucocorticoid receptor (GR) located in almost all brain cells; the GR is subsequently phosphorylated at serine 232 (pGRser232). This has been reported as an indicator of ligand-dependent activation of the GR, as well as a requirement for its translocation into the nucleus for its transcription factor activity. The GR is present in the hippocampus with a high concentration in CA1 and dentate gyrus (DG), and a smaller proportion in CA3, and sparsely present in the caudate putamen (CPu); both structures are involved in memory consolidation of IA. To study the participation of CORT in IA, we quantified the ratio of pGR-positive neurons in both dorsal hippocampus (CA1, CA3 and DG) and dorsal and ventral regions of CPu of rats trained in IA, using different foot-shock intensities. Brains were dissected 60 min after training for immunodetection of pGRser232 positive cells. The results show that the groups trained with 1.0 and 2.0 mA had higher retention latencies than the 0.0 mA or 0.5 mA groups. An increase in the ratio of pGR-positive neurons was found in CA1 and ventral region of CPu only for the 2.0 mA trained group. These findings suggest that activation of GRs in CA1 and ventral CPu is involved in the consolidation of a stronger memory of IA, possibly through the modulation of gene expression.

Dynamics of Dendritic Spines in Dorsal Striatum after Retrieval of Moderate and Strong Inhibitory Avoidance Learning.

In marked contrast to the ample literature showing that the dorsal striatum is engaged in memory consolidation, little is known about its involvement in memory retrieval. Recent findings demonstrated significant increments in dendritic spine density and mushroom spine counts in dorsal striatum after memory consolidation of moderate inhibitory avoidance (IA) training; further increments were found after strong training. Here, we provide evidence that in this region spine counts were also increased as a consequence of retrieval of moderate IA training, and even higher mushroom spine counts after retrieval of strong training; by contrast, there were fewer thin spines after retrieval. Similar changes in mushroom and thin spine populations were found in the ventral striatum (nucleus accumbens), but they were related to the aversive stimulation and not to memory retrieval. These results suggest that memory retrieval is a dynamic process which produces neuronal structural plasticity that might be necessary for maintaining or strengthening assemblies that encode stored information.

Corticosterone in the dorsolateral striatum facilitates the extinction of stimulus-response memory.

Glucocorticoid hormones are crucially involved in modulating mnemonic processing of stressful or emotionally arousing experiences. They are known to enhance the consolidation of new memories, including those that extinguish older memories. In this study, we investigated whether glucocorticoids facilitate the extinction of a striatum-dependent, and behaviorally more rigid, stimulus-response memory. For this, male rats were initially trained for six days on a stimulus-response task in a T-maze to obtain a reward after making an egocentric right-turn body response, regardless of the starting position in this maze. This training phase was followed by three extinction sessions in which right-turn body responses were not reinforced. Corticosterone administration into the dorsolateral region of the striatum after the first extinction session dose-dependently enhanced the consolidation of extinction memory: Rats administered the higher dose of corticosterone (30 ng), but not lower doses (5 or 10 ng), exhibited significantly fewer right-turn body responses and had longer latencies compared to vehicle-treated animals on the second and third extinction sessions. Co-administration of the glucocorticoid receptor antagonist RU 486 (10 ng) prevented the corticosterone effect, indicating that glucocorticoids enhance the extinction of stimulus-response memory via activation of the glucocorticoid receptor. Corticosterone administration into the dorsomedial striatum did not affect extinction memory. These findings indicate that stress-response mechanisms involving corticosterone actions in the dorsolateral striatum facilitate the extinction of stimulus-response memory that might allow for the development of an opportune behavioral strategy.

Imbalance in cerebral protein homeostasis: Effects on memory consolidation.

The long-standing hypothesis that memory consolidation is dependent upon de novo protein synthesis is based primarily on the amnestic effects of systemic administration of protein synthesis inhibitors (PSIs). Early experiments on mice showed that PSIs produced interference with memory consolidation that was dependent on the doses of PSIs, on the interval between drug injection and training, and, importantly, on the degree and duration of protein synthesis inhibition in the brain. Surprisingly, there is a conspicuous lack of information regarding the relationship between the duration of protein synthesis inhibition produced by PSIs and memory consolidation in the rat, one of the species most widely used to study memory processes. We found that, in the male rat, a single injection of cycloheximide, a commonly used PSI, produced a significant imbalance in protein homeostasis: an early inhibition of protein synthesis that lasted for at least one hour, followed by hyperproduction of proteins that lasted three days. We evaluated memory consolidation of inhibitory avoidance trained with either low or high intensity of foot-shock at the peaks of protein synthesis inhibition and protein hyperproduction. We found that, independent of the moment of training, the low-foot-shock groups showed amnesia, while the high-foot-shock groups displayed optimal memory performance. These results indicate that memory consolidation of relatively weak training is impaired by the inhibition or hyperproduction of protein synthesis, and that intense training overcomes this dysregulation of protein homeostasis allowing for memory formation probably through non-genomic mechanisms.

Differential Phosphorylation of the Glucocorticoid Receptor in Hippocampal Subregions Induced by Contextual Fear Conditioning Training.

Aversive events induce the release of glucocorticoid stress hormones that facilitate long-term memory consolidation, an effect that depends on the activation of glucocorticoid receptors (GRs). GRs are distributed widely in the hippocampus. The dorsal region of the hippocampus has been related to cognitive functions and the ventral region to stress and emotion. GR acts as a transcription factor which after hormone binding becomes phosphorylated, affecting its cellular distribution and transcriptional activity. Two functionally well-described GR phosphorylation sites are serine 232 (pSer232), which enhances gene expression, and serine 246 (pSer246), having the opposite effect. Since gene expression is one of the plastic mechanisms needed for memory consolidation, we investigated if an aversive learning task would induce GR phosphorylation in the dorsal (DH) and the ventral (VH) hippocampus. We trained rats in contextual fear conditioning (CFC) using different foot-shock intensities (0.0, 0.5, or 1.5 mA). One subgroup of animals trained with each intensity was sacrificed 15 min after training and blood was collected to quantify corticosterone (CORT) levels in serum. Another subgroup was sacrificed 1 h after training and brains were collected to evaluate the immunoreactivity (IR) to GR, pSer232 and pSer246 by SDS-PAGE/Western blot in DH and VH, and by immunohistochemistry in dorsal and ventral CA1, CA2, CA3, and dentate gyrus (DG) hippocampal regions. The conditioned freezing response increased in animals trained with 0.5 and 1.5 mA during training and extinction sessions. The degree of retention and CORT levels were directly related to the intensity of the foot-shock. Although total GR-IR remained unaffected after conditioning, we observed a significant increase of pSer246-IR in the dorsal region of CA1 and in both dorsal and ventral DG. The only region in which pSer232-IR was significantly elevated was ventral CA3. Our results indicate that fear conditioning training is related to GR phosphorylation in specific subregions of the hippocampus, suggesting that its transcriptional activity for gene expression is favored in ventral CA3, whereas its repressor activity for gene-silencing is increased in dorsal CA1 and in both dorsal and ventral DG.

Morris water maze overtraining increases the density of thorny excrescences in the basal dendrites of CA3 pyramidal neurons.

The hippocampus plays a fundamental role in spatial learning and memory. Dentate gyrus (DG) granular neurons project mainly to proximal apical dendrites of neurons in the CA3 stratum lucidum and also, to some extent, to the basal dendrites of CA3 pyramidal cells in the stratum oriens. The terminal specializations of DG neurons are the mossy fibers (MF), and these huge axon terminals show expansion in the CA3 stratum oriens after the animals undergo overtraining in the Morris Water Maze task (MWM). However, to our knowledge there are no reports regarding the possible changes in density of post-synaptic targets of these terminals in the basal dendrites of CA3 neurons after overtraining in the MWM. The purpose of this work was to study the density of thorny excrescences (TE) and other dendritic spine types (stubby, thin, and mushroom) in the CA3 stratum oriens in animals overtrained in the MWM for three consecutive days and in animals trained for only one day. Seven days after MWM training, the animals were sacrificed, and their brains removed and processed for rapid Golgi staining to visualize the different types of dendritic protrusions. Our results revealed that the relative quantity of stubby, thin, and mushroom dendritic spines did not change, regardless of amount of training. However, a significant increase in the density of TE was detected in the overtrained animals. These results strongly suggest that spatial water maze overtraining induces an increased density of MF-TE connections, which might be functionally relevant for long-term spatial memory formation.

Inhibition of transcription and translation in dorsal hippocampus does not interfere with consolidation of memory of intense training.

Findings of several experiments indicate that many treatments that typically interfere with memory consolidation are ineffective in preventing or attenuating memory induced by intense training. As extensive evidence suggests that the consolidation of newly acquired memories requires gene expression and de novo protein synthesis the present study investigated whether intense training prevents consolidation impairment induced by blockers of mRNA and protein synthesis. Rats were given a single inhibitory training trial using a moderate (1.0 mA) or a relatively intense (2.0 mA) foot-shock. Bilateral hippocampal infusions of the mRNA synthesis blocker DRB (10, 40 or 80 ng/0.5 µL/hemisphere) or the protein synthesis inhibitor anisomycin (ANI), an inhibitor de novo protein synthesis (15.62, 31.25, or 62.50 µg/0.5 µL/hemisphere) were administered 15 min prior to training. Retention was measured at 30 min or 48 h following training. DRB and ANI impaired memory of moderate training in a dose-dependent manner without affecting short-term memory. In contrast, memory consolidation was not impaired in the groups trained with 2.0 mA. The findings showed that: (1) inhibitors of transcription and translation in the hippocampus impair the consolidation of memory of inhibitory avoidance learning induced by moderate levels of aversive stimulation and (2) blocking of mRNA and protein synthesis does not prevent the consolidation of memory induced by relatively high levels of aversive stimulation. These findings do not support the hypothesis that gene expression and de novo protein synthesis are necessary steps for long-term memory formation as memory was not impaired if intense foot-shock was used in training.

Effects of anisomycin infusions into the dorsal striatum on memory consolidation of intense training and neurotransmitter activity.

The most influential hypothesis about the neurobiological basis of memory consolidation posits that this process is dependent upon de novo protein synthesis. Strong support for this proposition has been provided by a multitude of experiments showing that protein synthesis inhibitors (PSIs) interfere with consolidation. However, this hypothesis has been challenged by the results of studies showing that PSIs also produce a host of side effects that, by themselves, could account for their amnestic effects. It has been demonstrated that amnestic treatments become innocuous when administered to animals that have been subjected to intense training in a variety of learning tasks. We now report that while infusion of anisomycin (ANI), a PSI, into the dorsal striatum (DS) impairs memory consolidation of inhibitory avoidance learning in response to moderate aversive stimuli, such impairment by ANI is overcome by application of an intense stimulus. We also confirmed that ANI induces inhibition of protein synthesis in the DS, as evidenced by a reduction of the activity-regulated cytoskeletal associated protein (Arc). We found, for the first time, that ANI also induces an increased concentration of serotonin in the DS, which, by itself, may account for the interference with memory consolidation. These findings suggest that de novo protein synthesis in the dorsal striatum is not necessary for the consolidation of intense emotionally arousing experiences. The possibility of a non-genomic-dependent mechanism of memory consolidation is discussed.

Glucocorticoid interactions with the dorsal striatal endocannabinoid system in regulating inhibitory avoidance memory.

The endocannabinoid (eCB) system is highly stress sensitive and known to modulate memory formation of emotionally arousing experiences across different corticolimbic structures. eCB signaling within these circuits is also essentially involved in regulating non-genomically mediated glucocorticoid hormone effects on memory. It has long been thought that the dorsal striatum, which plays a major role in procedural memory and habit formation, is considerably less impacted by stressful experiences; however, recent findings indicate that stress and glucocorticoids also affect striatal-dependent memory processes. Yet, to what extent eCB signaling within the dorsal striatum may mediate such glucocorticoid effects on memory consolidation is currently unknown. Here we show, in male Wistar rats, that the cannabinoid agonist WIN55,212-2 administered into the dorsal striatum immediately after an inhibitory avoidance training experience dose-dependently enhanced 48-h retention performance. Conversely, the cannabinoid type 1 receptor (CB1R) antagonist AM251 impaired retention when administered into the dorsal striatum after inhibitory avoidance training. Most importantly, antagonism of striatal CB1R activity with AM251 completely abolished the effect of corticosterone or of the membrane-impermeable ligand corticosterone:BSA administered posttraining into the dorsal striatum or injected systemically on enhancement of inhibitory avoidance memory. Further, suppression of glucocorticoid signaling by systemic injection of the corticosterone-synthesis inhibitor metyrapone also impaired the memory-enhancing effect of intra-striatal WIN55, 212-2 administration. These findings indicate that the eCB system, in close interaction with glucocorticoid signaling, is involved in modulating plasticity changes underlying memory consolidation not only in corticolimbic structures but also within the dorsal striatum.

Retrieval of Inhibitory Avoidance Memory Induces Differential Transcription of arc in Striatum, Hippocampus, and Amygdala.

Similar to the hippocampus and amygdala, the dorsal striatum is involved in memory retrieval of inhibitory avoidance, a task commonly used to study memory processes. It has been reported that memory retrieval of fear conditioning regulates gene expression of arc and zif268 in the amygdala and the hippocampus, and it is surprising that only limited effort has been made to study the molecular events caused by retrieval in the striatum. To further explore the involvement of immediate early genes in retrieval, we used real-time PCR to analyze arc and zif268 transcription in dorsal striatum, dorsal hippocampus, and amygdala at different time intervals after retrieval of step-through inhibitory avoidance memory. We found that arc expression in the striatum increased 30 min after retrieval while no changes were observed in zif268 in this region. Expression of arc and zif268 also increased in the dorsal hippocampus but the changes were attributed to context re-exposure. Control procedures indicated that in the amygdala, arc and zif268 expression was not dependent on retrieval. Our data indicate that memory retrieval of inhibitory avoidance induces arc gene expression in the dorsal striatum, caused, very likely, by the instrumental component of the task. Striatal arc expression after retrieval may induce structural and functional changes in the neurons involved in this process.

Differential Effects of Inactivation of Discrete Regions of Medial Prefrontal Cortex on Memory Consolidation of Moderate and Intense Inhibitory Avoidance Training.

It has been found that the medial prefrontal cortex (mPFC) is involved in memory encoding of aversive events, such as inhibitory avoidance (IA) training. Dissociable roles have been described for different mPFC subregions regarding various memory processes, wherein the anterior cingulate cortex (ACC), prelimbic cortex (PL), and infralimbic cortex (IL) are involved in acquisition, retrieval, and extinction of aversive events, respectively. On the other hand, it has been demonstrated that intense training impedes the effects on memory of treatments that typically interfere with memory consolidation. The aim of this work was to determine if there are differential effects on memory induced by reversible inactivation of neural activity of ACC, PL, or IL produced by tetrodotoxin (TTX) in rats trained in IA using moderate (1.0 mA) and intense (3.0 mA) foot-shocks. We found that inactivation of ACC has no effects on memory consolidation, regardless of intensity of training. PL inactivation impairs memory consolidation in the 1.0 mA group, while no effect on consolidation was produced in the 3.0 mA group. In the case of IL, a remarkable amnestic effect in LTM was observed in both training conditions. However, state-dependency can explain the amnestic effect of TTX found in the 3.0 mA IL group. In order to circumvent this effect, TTX was injected into IL immediately after training (thus avoiding state-dependency). The behavioral results are equivalent to those found after PL inactivation. Therefore, these findings provide evidence that PL and IL, but not ACC, mediate LTM of IA only in moderate training.

Glucocorticoid administration into the dorsolateral but not dorsomedial striatum accelerates the shift from a spatial toward procedural memory.

Glucocorticoid stress hormones are known to enhance the consolidation of hippocampus-dependent spatial and contextual memory. Recent findings indicate that glucocorticoids also enhance the consolidation of procedural memory that relies on the dorsal striatum. The dorsal striatum can be functionally subdivided into the dorsolateral striatum (DLS), which is primarily implicated in shaping procedural memories, and the dorsomedial striatum (DMS), which is engaged in spatial memory. Here, we investigated the hypothesis that posttraining glucocorticoid administration into the DLS promotes the formation of a procedural memory that will normally take place only with extensive training. Male Wistar rats were trained to find a reward in a cross maze that can be solved through either place or response learning. Rats received four trials per day for 5days, a probe trial on Day 6, further training on Days 7-13, and an additional probe trial on Day 14. On Days 2-4 of training, they received posttraining infusions of corticosterone (10 or 30ng) or vehicle into either the DLS or DMS. Rats treated with vehicle into either the DLS or DMS displayed place learning on Day 6 and response learning on Day 14, indicating a shift in control of learned behavior toward a habit-like procedural strategy with extended training. Rats administered corticosterone (10ng) into the DLS displayed response learning on both Days 6 and 14, indicating an accelerated shift to response learning. In contrast, corticosterone administered posttraining into the DMS did not significantly alter the shift from place to response learning. These findings indicate that glucocorticoid administration into the DLS enhances memory consolidation of procedural learning and thereby influences the timing of the switch from the use of spatial/contextual memory to habit-like procedural memory to guide behavior.

Differential Arc protein expression in dorsal and ventral striatum after moderate and intense inhibitory avoidance training.

Intense training refers to training mediated by emotionally arousing experiences, such as aversive conditioning motivated by relatively high intensities of foot-shock, which produces a strong memory that is highly resistant to extinction. Intense training protects memory consolidation against the amnestic effects of a wide variety of treatments, administered systemically or directly into brain structures. The mechanisms of this protective effect are unknown. To determine a potential neurobiological correlate of the protective effect of intense training, rats were trained in a one-trial step-through inhibitory avoidance task using different intensities of foot-shock (0.0, 0.5, 1.0, and 2.0mA). Some rats from each group were sacrificed 45min after training for immunohistochemical Arc protein detection in dorsal and ventral striatum; other rats were tested for extinction during six consecutive days, starting 48h after training. The results showed that training with 1.0 and 2.0mA produced optimal retention scores, which were significantly higher than those of the 0.5 and 0.0mA groups. Also, a higher resistance to extinction was obtained with 2.0mA than with the other intensities. A high number of neurons expressed Arc in ventral, but not in dorsal striatum in both the 1.0 and 2.0mA groups, with a larger area of Arc signal in the latter group. We conclude that an increased Arc expression may be related to enhanced synaptic plasticity in the ventral striatum, suggesting that it may be one of the physiological substrates of enhanced learning.

Inhibition of transcription and translation in the striatum after memory reactivation: Lack of evidence of reconsolidation.

It has been found that interference with neural activity after a consolidated memory is retrieved produces an amnestic state; this has been taken has indicative of destabilization of the memory trace that would have been produced by a process of reconsolidation (allowing for maintenance of the original trace). However, a growing body of evidence shows that this is not a reliable effect, and that it is dependent upon some experimental conditions, such as the age of the memory, memory reactivation procedures, the predictability of the reactivation stimulus, and strength of training. In some instances, where post-retrieval treatments induce a retention deficit (which would be suggestive of interference with reconsolidation), memory is rescued by simple passing of time or by repeated retention tests. We now report that post-training and post-retrieval inhibition of transcription and translation in dorsal striatum, a structure where both of these manipulations have not been studied, produce interference with consolidation and a transitory retention deficit, respectively. These results do not give support to the reconsolidation hypothesis and lead to the conclusion that the post-activation deficiencies are due to interference with retrieval of information.

Development of Emotional Face Processing in Premature and Full-Term Infants.

The rate of premature births has increased in the past 2 decades. Ten percent of premature birth survivors develop motor impairment, but almost half exhibit later sensorial, cognitive, and emotional disabilities attributed to white matter injury and decreased volume of neuronal structures. The aim of this study was to test the hypothesis that premature and full-term infants differ in their development of emotional face processing. A comparative longitudinal study was conducted in premature and full-term infants at 4 and 8 months of age. The absolute power of the electroencephalogram was analyzed in both groups during 5 conditions of an emotional face processing task: positive, negative, neutral faces, non-face, and rest. Differences between the conditions of the task at 4 months were limited to rest versus non-rest comparisons in both groups. Eight-month-old term infants had increases ( P ≤ .05) in absolute power in the left occipital region at the frequency of 10.1 Hz and in the right occipital region at 3.5, 12.8, and 16.0 Hz when shown a positive face in comparison with a neutral face. They also showed increases in absolute power in the left occipital region at 1.9 Hz and in the right occipital region at 2.3 and 3.5 Hz with positive compared to non-face stimuli. In contrast, positive, negative, and neutral faces elicited the same responses in premature infants. In conclusion, our study provides electrophysiological evidence that emotional face processing develops differently in premature than in full-term infants, suggesting that premature birth alters mechanisms of brain development, such as the myelination process, and consequently affects complex cognitive functions.

Mushroom spine dynamics in medium spiny neurons of dorsal striatum associated with memory of moderate and intense training.

A growing body of evidence indicates that treatments that typically impair memory consolidation become ineffective when animals are given intense training. This effect has been obtained by treatments interfering with the neural activity of several brain structures, including the dorsal striatum. The mechanisms that mediate this phenomenon are unknown. One possibility is that intense training promotes the transfer of information derived from the enhanced training to a wider neuronal network. We now report that inhibitory avoidance (IA) induces mushroom spinogenesis in the medium spiny neurons (MSNs) of the dorsal striatum in rats, which is dependent upon the intensity of the foot-shock used for training; that is, the effect is seen only when high-intensity foot-shock is used in training. We also found that the relative density of thin spines was reduced. These changes were evident at 6 h after training and persisted for at least 24 h afterward. Importantly, foot-shock alone did not increase spinogenesis. Spine density in MSNs in the accumbens was also increased, but the increase did not correlate with the associative process involved in IA; rather, it resulted from the administration of the aversive stimulation alone. These findings suggest that mushroom spines of MSNs of the dorsal striatum receive afferent information that is involved in the integrative activity necessary for memory consolidation, and that intense training facilitates transfer of information from the dorsal striatum to other brain regions through augmented spinogenesis.