Tool-use learning selectively induces expression of brain-derived neurotrophic factor, its receptor trkB, and neurotrophin 3 in the intraparietal multisensorycortex of monkeys

The parietal lobe evolution and the emergence of material culture in the human genus

Traditional and new disciplines converge in suggesting that the parietal lobe underwent a considerable expansion during human evolution. Through the study of endocasts and shape analysis, paleoneurology has shown an increased globularity of the braincase and bulging of the parietal region in modern humans, as compared to other human species, including Neandertals. Cortical complexity increased in both the superior and inferior parietal lobules. Emerging fields bridging archaeology and neuroscience supply further evidence of the involvement of the parietal cortex in human-specific behaviors related to visuospatial capacity, technological integration, self-awareness, numerosity, mathematical reasoning and language. Here, we complement these inferences on the parietal lobe evolution, with results from more classical neuroscience disciplines, such as behavioral neurophysiology, functional neuroimaging, and brain lesions; and apply these to define the neural substrates and the role of the parietal lobes in the emergence of functions at the core of material culture, such as tool-making, tool use and constructional abilities.

Pedagogical Ecology for an Alternative Sustainability: With Insights from Francis of Assisi and Contemporary Life Sciences

Sustainability is a widely discussed issue nowadays. The “human factor” appears to be the key to a suitable theory of sustainable development and, even more, to understanding the real scope of the issue at stake. We begin by highlighting that the issue of sustainability and the related ecological crisis ultimately stem from the fundamental view of the human–environment relationships. We tackle such a fundamental view from two apparently distant but converging perspectives: the one of Francis of Assisi (the patron saint of ecologists) and the one of contemporary advancements in evolutionary biology known as the “extended evolutionary theory” (EES). This will allow us to highlight how current life sciences ground a strong form of organism–environment complementarity—a core point for any allegedly comprehensive approach to sustainability and ecology. After that, we focus on recent developments in cultural evolution studies that see culture both as the driving force of (recent) human evolution and as the general context where the human–environment relationships take place and develop. Therefore, we argue that the environment exerts a powerful pedagogical influence on the human being and on humanity as a whole. We conclude by proposing a pedagogical criterion for ecology and sustainable development, according to which the modifications caused by the human being to the environment must be assessed (also) for their pedagogical import.

Rats' (Rattus norvegicus) tool manipulation ability exceeds simple patterned behavior

Many studies have attempted to shed light on the ability of non-human animals to understand physical causality by investigating their tool-use behavior. This study aimed to develop a tool-manipulation task for rodents in which the subjects could not manipulate the tool in the direction of the reward by simple patterned behavior. Eight rats had to use a rake-shaped tool to obtain a food reward placed beyond their reach. During the training, the rats never moved the rakes laterally to obtain the reward. However, in the positional discrimination test, the rake was placed at the center of the experimental apparatus, and the reward was positioned on either the left or right side of the rake. Interestingly, this test indicated that some rats were able to manipulate the rake toward the reward without relying on a patterned behavior acquired during the training. These results suggested that rats have the primitive ability to understand causal relationships in the physical environment. The findings indicate that rats can potentially serve as an animal model to investigate the mechanisms of evolution and development of the understanding of physical causality in humans.

Tool manipulation by rats (Rattus norvegicus) according to the position of food

Tool-use behaviour has been observed in nonhuman animals in the wild and in experimental settings. In the present study, we investigated whether rats (Rattus norvegicus) could manipulate a tool according to the position of food to obtain the food in an experimental setting. Eight rats were trained to use a rake-shaped tool to obtain food beyond their reach using a step-by-step protocol in the initial training period. Following training, the rake was placed at the centre of the experimental apparatus, and food was placed on either the left or right side of the rake. Rats learned to manipulate the rake to obtain food in situations in which they could not obtain the food just by pulling the rake perpendicularly to themselves. Our findings thus indicate that the rat is a potential animal model to investigate the behavioural and neural mechanisms of tool-use behaviour.

BDNF as a possible modulator of EEG oscillatory response at the parietal cortex during visuo-tactile integration processes using a rubber hand

Multisensory integration of visuo-tactile information presented on the body or a dummy body has a strong impact on body image. Previous researches show that alteration of body image induced by visuo-tactile integration is closely related to the activation of the parietal cortex, a sensory association area. The expression of brain-derived neurotrophic factor (BDNF) in the parietal area of macaque monkeys is thought to modulate the activation of the parietal cortex and alter the extension of body image during tool-use learning. However, the relationship between parietal cortex activation related to body image alterations and BDNF levels in humans remains unclear. We investigated the relationship between human serum BDNF levels and electroencephalography responses during a visuo-tactile integration task involving a rubber hand. We found cortical oscillatory components in the high frequency (gamma) band in the left parietal cortex. Moreover, the power values of these oscillations were positively correlated (p<0.05) with serum BDNF levels. Our results suggest that serum BDNF could play a role in modulating the cortical activity in response to visuo-tactile integration processes related to body image alteration in humans.

Mirror neurons in the tree of life: mosaic evolution, plasticity and exaptation of sensorimotor matching responses

Considering the properties of mirror neurons (MNs) in terms of development and phylogeny, we offer a novel, unifying, and testable account of their evolution according to the available data and try to unify apparently discordant research, including the plasticity of MNs during development, their adaptive value and their phylogenetic relationships and continuity. We hypothesize that the MN system reflects a set of interrelated traits, each with an independent natural history due to unique selective pressures, and propose that there are at least three evolutionarily significant trends that gave raise to three subtypes: hand visuomotor, mouth visuomotor, and audio-vocal. Specifically, we put forward a mosaic evolution hypothesis, which posits that different types of MNs may have evolved at different rates within and among species. This evolutionary hypothesis represents an alternative to both adaptationist and associative models. Finally, the review offers a strong heuristic potential in predicting the circumstances under which specific variations and properties of MNs are expected. Such predictive value is critical to test new hypotheses about MN activity and its plastic changes, depending on the species, the neuroanatomical substrates, and the ecological niche.

Identification of tool use acquisition-associated genes in the primate neocortex

Japanese macaques are able to learn how to use rakes to take food after only a few weeks of training. Since tool-use training induced rapid morphological changes in some restricted brain areas, this system will be a good model for studying the neural basis of plasticity in human brains. To examine the mechanisms of tool-use associated brain expansion on the molecular and cellular level, here, we performed comprehensive analysis of gene expressions with microarray. We identified various transcripts showing differential expression between trained and untrained monkeys in the region around the lateral and intraparietal sulci. Among candidates, we focused on genes related to synapse formation and function. Using quantitative reverse transcription-polymerase chain reaction and histochemical analysis, we confirmed at least three genes (ADAM19, SPON2, and WIF1) with statistically different expression levels in neurons and glial cells. Comparative analysis revealed that tool use-associated genes were more obviously expressed in macaque monkeys than marmosets or mice. Thus, our findings suggest that cognitive tasks induce structural changes in the neocortex via gene expression, and that learning-associated genes innately differ with relation to learning ability.

Augmentation-related brain plasticity

Today, the anthropomorphism of the tools and the development of neural interfaces require reconsidering the concept of human-tools interaction in the framework of human augmentation. This review analyses the plastic process that the brain undergoes when it comes into contact with augmenting artificial sensors and effectors and, on the other hand, the changes that the use of external augmenting devices produces in the brain. Hitherto, few studies investigated the neural correlates of augmentation, but clues on it can be borrowed from logically-related paradigms: sensorimotor training, cognitive enhancement, cross-modal plasticity, sensorimotor functional substitution, use and embodiment of tools. Augmentation modifies function and structure of a number of areas, i.e., primary sensory cortices shape their receptive fields to become sensitive to novel inputs. Motor areas adapt the neuroprosthesis representation firing-rate to refine kinematics. As for normal motor outputs, the learning process recruits motor and premotor cortices and the acquisition of proficiency decreases attentional recruitment, focuses the activity on sensorimotor areas and increases the basal ganglia drive on the cortex. Augmentation deeply relies on the frontoparietal network. In particular, premotor cortex is involved in learning the control of an external effector and owns the tool motor representation, while the intraparietal sulcus extracts its visual features. In these areas, multisensory integration neurons enlarge their receptive fields to embody supernumerary limbs. For operating an anthropomorphic neuroprosthesis, the mirror system is required to understand the meaning of the action, the cerebellum for the formation of its internal model and the insula for its interoception. In conclusion, anthropomorphic sensorized devices can provide the critical sensory afferences to evolve the exploitation of tools through their embodiment, reshaping the body representation and the sense of the self.

Tool-use practice induces changes in intrinsic functional connectivity of parietal areas

Intrinsic functional connectivity from resting state functional magnetic resonance imaging (rsfMRI) has increasingly received attention as a possible predictor of cognitive function and performance. In this study, we investigated the influence of practicing skillful tool manipulation on intrinsic functional connectivity in the resting brain. Acquisition of tool-use skill has two aspects such as formation of motor representation for skillful manipulation and acquisition of the tool concept. To dissociate these two processes, we chose chopsticks-handling with the non-dominant hand. Because participants were already adept at chopsticks-handling with their dominant hand, practice with the non-dominant hand involved only acquiring the skill for tool manipulation with existing knowledge. Eight young participants practiced chopsticks-handling with their non-dominant hand for 8 weeks. They underwent functional magnetic resonance imaging (fMRI) sessions before and after the practice. As a result, functional connectivity among tool-use-related regions of the brain decreased after practice. We found decreased functional connectivity centered on parietal areas, mainly the supramarginal gyrus (SMG) and superior parietal lobule (SPL) and additionally between the primary sensorimotor area and cerebellum. These results suggest that the parietal lobe and cerebellum purely mediate motor learning for skillful tool-use. This decreased functional connectivity may represent increased efficiency of functional network.

Triadic (ecological, neural, cognitive) niche construction: a scenario of human brain evolution extrapolating tool use and language from the control of reaching actions

Hominin evolution has involved a continuous process of addition of new kinds of cognitive capacity, including those relating to manufacture and use of tools and to the establishment of linguistic faculties. The dramatic expansion of the brain that accompanied additions of new functional areas would have supported such continuous evolution. Extended brain functions would have driven rapid and drastic changes in the hominin ecological niche, which in turn demanded further brain resources to adapt to it. In this way, humans have constructed a novel niche in each of the ecological, cognitive and neural domains, whose interactions accelerated their individual evolution through a process of triadic niche construction. Human higher cognitive activity can therefore be viewed holistically as one component in a terrestrial ecosystem. The brain's functional characteristics seem to play a key role in this triadic interaction. We advance a speculative argument about the origins of its neurobiological mechanisms, as an extension (with wider scope) of the evolutionary principles of adaptive function in the animal nervous system. The brain mechanisms that subserve tool use may bridge the gap between gesture and language—the site of such integration seems to be the parietal and extending opercular cortices.

Tool-use learning by common marmosets (Callithrix jacchus)

One of the most critical and common features of tool use is that the tool essentially functions as a part of the body. This feature is likely rooted in biological features that are shared by tool users. To establish an ideal primate model to explore the neurobiological mechanisms supporting tool-use behaviours, we trained common marmosets, a small New World monkey species that is not usually associated with tool use, to use a rake-shaped tool to retrieve food. Five naive common marmosets were systematically trained to manipulate the tool using a 4-stage, step-by-step protocol. The relative positions of the tool and the food were manipulated, so that the marmosets were required to (1) pull the tool vertically, (2) move the tool horizontally, (3) make an arc to retrieve a food item located behind the tool and (4) retrieve the food item. We found considerable individual differences in tool-use technique; for example, one animal consistently used a unilateral hand movement for all of the steps, whereas the others (n = 4) used both hands to move the tool depending on the location of the food item. After extensive training, all of the marmosets could manipulate the rake-shaped tool, which is reported in this species for the first time. The common marmoset is thus a model primate for such studies. This study sets the stage for future research to examine the biological mechanisms underlying the cognitive ability of tool use at the molecular and genetic levels.

Genetic influences on neural plasticity

Neural plasticity refers to the capability of the brain to alter function or structure in response to a range of events and is a crucial component of both functional recovery after injury and skill learning in healthy individuals. A number of factors influence neural plasticity and recovery of function after brain injury. The current review considers the impact of genetic factors. Polymorphisms in the human genes coding for brain-derived neurotrophic factor and apolipoprotein E have been studied in the context of plasticity and stroke recovery and are discussed here in detail. Several processes involved in plasticity and stroke recovery, such as depression or pharmacotherapy effects, are modulated by other genetic polymorphisms and are also discussed. Finally, new genetic polymorphisms that have not been studied in the context of stroke are proposed as new directions for study. A better understanding of genetic influences on recovery and response to therapy might allow improved treatment after a number of forms of central nervous system injury.

Brain plasticity and genetic factors

Brain plasticity refers to changes in brain function and structure that arise in a number of contexts. One area in which brain plasticity is of considerable interest is recovery from stroke, both spontaneous and treatment-induced. A number of factors influence these poststroke brain events. The current review considers the impact of genetic factors. Polymorphisms in the human genes coding for brain-derived neurotrophic factor (BDNF) and apolipoprotein E (ApoE) have been studied in the context of plasticity and/or stroke recovery and are discussed here in detail. Several other genetic polymorphisms are indirectly involved in stroke recovery through their modulating influences on processes such as depression and pharmacotherapy effects. Finally, new genetic polymorphisms that have not been studied in the context of stroke are proposed as new directions for study. A better understanding of genetic influences on recovery and response to therapy might allow improved treatment after stroke.

Gray and white matter changes associated with tool-use learning in macaque monkeys

We used noninvasive MRI and voxel-based morphometry (VBM) to detect changes in brain structure in three adult Japanese macaques trained to use a rake to retrieve food rewards. Monkeys, who were naive to any previous tool use, were scanned repeatedly in a 4-T scanner over 6 weeks, comprising 2 weeks of habituation followed by 2 weeks of intensive daily training and a 2-week posttraining period. VBM analysis revealed significant increases in gray matter with rake performance across the three monkeys. The effects were most significant (P < 0.05 corrected for multiple comparisons across the whole brain) in the right superior temporal sulcus, right second somatosensory area, and right intraparietal sulcus, with less significant effects (P < 0.001 uncorrected) in these same regions of the left hemisphere. Bilateral increases were also observed in the white matter of the cerebellar hemisphere in lobule 5. In two of the monkeys who exhibited rapid learning of the rake task, gray matter volume in peak voxels increased by up to 17% during the intensive training period; the earliest changes were seen after 1 week of intensive training, and they generally peaked when performance on the task plateaued. In the third monkey, who was slower to learn the task, peak voxels showed no systematic changes. Thus, VBM can detect significant brain changes in individual trained monkeys exposed to tool-use training for the first time. This approach could open up a means of investigating the underlying neurobiology of motor learning and other higher brain functions in individual animals.

The neuroscience of primate intellectual evolution: natural selection and passive and intentional niche construction

We trained Japanese macaque monkeys to use tools, an advanced cognitive function monkeys do not exhibit in the wild, and then examined their brains for signs of modification. Following tool-use training, we observed neurophysiological, molecular genetic and morphological changes within the monkey brain. Despite being 'artificially' induced, these novel behaviours and neural connectivity patterns reveal overlap with those of humans. Thus, they may provide us with a novel experimental platform for studying the mechanisms of human intelligence, for revealing the evolutionary path that created these mechanisms from the 'raw material' of the non-human primate brain, and for deepening our understanding of what cognitive abilities are and of those that are not uniquely human. On these bases, we propose a theory of 'intentional niche construction' as an extension of natural selection in order to reveal the evolutionary mechanisms that forged the uniquely intelligent human brain.

A neural network model of multisensory representation of peripersonal space: effect of tool use

This work describes an original neural network to simulate representation of the peripersonal space around one hand, in basal conditions and after training with a tool used to reach the far space. The model is composed of two unimodal areas (visual and tactile) connected to a third bimodal area (visual-tactile). Neurons in the bimodal area integrate visual and tactile information and are activated only when a stimulus falls inside the peripersonal space. Moreover, the model assumes that synapses linking unimodal to bimodal neurons can be reinforced by an Hebbian rule during training, but this reinforcement is also under the influence of attention mechanisms. Results show that the peripersonal space, which includes just a small visual space around the hand in normal conditions, becomes elongated in the direction of the tool after training. This expansion of the peripersonal space depends on an expansion of the visual receptive field of bimodal neurons, due to a reinforcement of visual synapses, which were just latent before training. The model may be of value to analyze the neural mechanisms responsible for representing and plastically shaping peripersonal space, and in perspective, for interpretation of psychophysical data on patients with brain damage.

Cellular mechanisms underlying the effect of a single exposure to neonatal handling on neurotrophin-3 in the brain of 1-day-old rats

Neurotrophin-3 (NT-3) has an important role in brain development and is thus a good candidate molecule to be involved in the cellular mechanisms mediating the effects of early experiences on the brain. In the present work we employed the model of neonatal handling, which is known to affect the ability of the adult organism to respond to stressful stimuli, and determined its effects on NT-3 levels in the rat hippocampus and cortex 2, 4 and 8 h after handling on postnatal day 1. We also recorded maternal behavior during the 8 h following handling. At both the 4 and 8 h time-points there was an increase in NT-3 positive cells in field 1 of Ammon's horn (CA1 area of the hippocampus) and parietal cortex of the handled animals. In the parietal cortex NT-3 levels increased with time following handling: at 8 h there were more NT-3 positive cells than at 4 h. During the 4 h following the end of handling, handled pups were subject to more maternal licking, indicating that the more intense maternal care could underlie the handling-induced increase in NT-3. In the hippocampus, the handling induced increase in NT-3 was cancelled by inhibition of N-methyl-D-aspartate (NMDA), AMPA/kainate, or GABA-A receptors, as well as L-type voltage-gated Ca(2+) channels. It thus appears that neonatal handling activates these neurotransmitter receptors and channels, leading to increased intracellular Ca(2+) and increased NT-3 expression. NT-3 can then activate downstream effectors and exert its morphogenetic actions and thus imprint the effects of handling on the brain.

Does tool-related fMRI activity within the intraparietal sulcus reflect the plan to grasp?

Neuroimaging investigations reliably describe a left-lateralized network of areas as underlying the representations of knowledge about familiar tools. Among the critical 'nodes' of the network, an area centered within the left intraparietal sulcus (IPS) is thought to be related to the motoric representations associated with familiar tools and their usage. This area is in the vicinity of an area implicated in the control of object-directed grasping actions: the anterior intraparietal area, AIP. The current study aimed to evaluate whether this tool-related intraparietal activity could be accounted for by the graspable nature of tools or whether it was due to additional factors such as the functionality of tools. First, we found that during a naming task activation within a discrete region of the left anterior intraparietal cortex was higher for tools than for graspable objects, but did not differ between graspable and non-graspable objects. In addition, the peak activity associated with tool naming was found to be largely distinct and consistently posterior to that associated with real object grasping. A separate region, anterior to the tool-selective focus and possibly overlapping with AIP, demonstrated weak selectivity for both tools and graspable objects relative to non-graspable objects. These findings indicate that this tool-selective area at the anterior end of the left IPS is both separable from the grasp-related intraparietal activity and, consistently, it does not simply reflect the processing of grasping affordances. Taken together, these results suggest that object graspability alone cannot account for the left intraparietal activity driven by the naming of tools. Instead, this activity may relate to learned motor representations associated with the skillful use of familiar tools.

Tool-Use: Capturing Multisensory Spatial Attention or Extending Multisensory Peripersonal Space?

The active and skilful use of tools has been claimed to lead to the "extension" of the visual receptive fields of single neurons representing peripersonal space--the visual space immediately surrounding one's body parts. While this hypothesis provides an attractive and potentially powerful explanation for one neural basis of tool-use behaviours in human and nonhuman primates, a number of competing hypotheses for the reported behavioural effects of tool-use have not yet been subjected to empirical test. Here, we report five behavioural experiments in healthy human participants (n=120) involving the effects of tool-use on visual-tactile interactions in peripersonal space. Specifically, we address the possibility that the use of only a single tool, which is typical of many neuropsychological studies of tool-use, induces a spatial allocation of attention towards the side where the tool is held. Participants' tactile discrimination responses were more strongly affected by visual stimuli presented on the right side when they held a single tool on the right, compared to visual stimuli presented on the left. When [corrected] two tools were held, one in each hand, this spatial effect disappeared. Our results are incompatible with the hypothesis that tool-use extends peripersonal space, and suggest instead that the use and/or manipulation of [corrected] tools results in an automatic multisensory shift of spatial attention to the side of space where the tip of the tool is actively held. These results have implications for many of the cognitive neuroscientific studies of tool-use published to date.

Relational spatial reasoning by a nonhuman: the example of capuchin monkeys

The authors review spontaneous manipulation and spatial problem solving by capuchin monkeys to illuminate the nature of relational reasoning (wherein two or more elements of a problem or situation are considered together to arrive at a course of action) that these monkeys use in goal-directed activity. Capuchin monkeys master problems with one, two, or three spatial relations, and if more than one relation, at least two relations may be managed concurrently. They can master static and dynamic relations and, with sufficient practice, can produce specific spatial relations through both direct and distal action. Examining capuchins' spatial problem-solving behavior with objects in the framework of a spatial relational reasoning model leads to new interpretations of previous studies with these monkeys and other nonhuman animals. The model produces a variety of testable predictions concerning the contribution of relational properties to spatial reasoning. It also provides conceptual linkages with neurological processes and cognitive analyses of physical reasoning. Understanding relational spatial reasoning, including tool use, in a wider view is vital to informed, principled comparison of problem solving and the use of technology across species, across ages within species, and across eras in human prehistory.

Extension of corticocortical afferents into the anterior bank of the intraparietal sulcus by tool-use training in adult monkeys

When humans use a tool, it becomes an extension of the hand physically and perceptually. Common introspection might occur in monkeys trained in tool-use, which should depend on brain operations that constantly update and automatically integrate information about the current intrinsic (somatosensory) and the extrinsic (visual) status of the body parts and the tools. The parietal cortex plays an important role in using tools. Intraparietal neurones of naïve monkeys mostly respond unimodally to somatosensory stimuli; however, after training these neurones become bimodally active and respond to visual stimuli. The response properties of these neurones change to code the body images modified by assimilation of the tool to the hand holding it. In this study, we compared the projection patterns between visually related areas and the intraparietal cortex in trained and naïve monkeys using tracer techniques. Light microscopy analyses revealed the emergence of novel projections from the higher visual centres in the vicinity of the temporo-parietal junction and the ventrolateral prefrontal areas to the intraparietal area in monkeys trained in tool-use, but not in naïve monkeys. Functionally active synapses of intracortical afferents arising from higher visual centres to the intraparietal cortex of the trained monkeys were confirmed by electron microscopy. These results provide the first concrete evidence for the induction of novel neural connections in the adult monkey cerebral cortex, which accompanies a process of demanding behaviour in these animals.

Tools for the body (schema)

What happens in our brain when we use a tool to reach for a distant object? Recent neurophysiological, psychological and neuropsychological research suggests that this extended motor capability is followed by changes in specific neural networks that hold an updated map of body shape and posture (the putative "Body Schema" of classical neurology). These changes are compatible with the notion of the inclusion of tools in the "Body Schema", as if our own effector (e.g. the hand) were elongated to the tip of the tool. In this review we present empirical support for this intriguing idea from both single-neuron recordings in the monkey brain and behavioural performance of normal and brain-damaged humans. These relatively simple neural and behavioural aspects of tool-use shed light on more complex evolutionary and cognitive aspects of body representation and multisensory space coding for action.

Multisensory contributions to the 3-D representation of visuotactile peripersonal space in humans: evidence from the crossmodal congruency task

In order to determine precisely the location of a tactile stimulus presented to the hand it is necessary to know not only which part of the body has been stimulated, but also where that part of the body lies in space. This involves the multisensory integration of visual, tactile, proprioceptive, and even auditory cues regarding limb position. In recent years, researchers have become increasingly interested in the question of how these various sensory cues are weighted and integrated in order to enable people to localize tactile stimuli, as well as to give rise to the 'felt' position of our limbs, and ultimately the multisensory representation of 3-D peripersonal space. We highlight recent research on this topic using the crossmodal congruency task, in which participants make speeded elevation discrimination responses to vibrotactile targets presented to the thumb or index finger, while simultaneously trying to ignore irrelevant visual distractors presented from either the same (i.e., congruent) or a different (i.e., incongruent) elevation. Crossmodal congruency effects (calculated as performance on incongruent-congruent trials) are greatest when visual and vibrotactile stimuli are presented from the same azimuthal location, thus providing an index of common position across different sensory modalities. The crossmodal congruency task has been used to investigate a number of questions related to the representation of space in both normal participants and brain-damaged patients. In this review, we detail the major findings from this research, and highlight areas of convergence with other cognitive neuroscience disciplines.

Monkey brain areas underlying remote-controlled operation

We can control distant tools effectively by manipulating other objects as controllers in various remote-operated ways, even when the two mechanics are altered. To master the remote operation, we may rely on internal representation to organize individual moves of the controller and tool into a set of sequences by mapping the motor space among hand, controller and tool as a continuum. The present study confirmed that monkeys could also organize a sequence by mapping such a motor space or reorganize by remapping even after alteration. In addition, to investigate the neural substrates underlying such mapping/remapping, we measured the regional cerebral blood flow of two monkeys during joystick-controlled operation with alterable function of mechanics using positron emission tomography with. The monkeys were scanned during three different tasks produced by altering the directional gains of the x or y axis of the joystick - the two mechanics are congruent (standard task) and not congruent (reversed in the X or Y axis, X reverse or Y reverse task, respectively). Compared with random movement of the joystick as the control task, increased activities were detected in the prefrontal cortex, higher-ordered motor cortex, posterior parietal cortex and cerebellum during the standard task. Common brain areas during performance of the X reverse and Y reverse task were identified as showing almost the same pattern as during the standard task. These shared areas may not simply be associated with organization of individual motor imagery, but also with context-dependent processing of reorganization based on current functions by means of internal representation.

Possible mechanism for transfer of motor skill learning: implication of the cerebellum

Transfer of learning takes place whenever our previous knowledge and skills affect the way in which new knowledge and skills are learned. The magnitude of transfer may depend on how prior memory is retrieved so that it may be relevant and usable in the present in terms of internal representation. This review highlights the power of neuroimaging techniques such as positron emission tomography (PET) to identify the underlying neuronal system of intermanual transfer by showing the asymmetry in the system for the same motor skill between hands. The review focuses on cerebellar cross-activation, cerebellar activation contralateral to the active hand, which would contribute to intermanual transfer of monkey tool-use learning, together with the fronto-parietal cortical circuit. Finally, this article proposes the relationship between the cerebellum and the possible mechanism underlying non-specific transfer that allows thinking in a flexible and productive manner.

Fronto-parieto-cerebellar interaction associated with intermanual transfer of monkey tool-use learning

Prior motor skill learning (original learning; OL) with one hand (original hand; OH) can affect relearning of the same skill (transfer learning; TL) with the opposite hand (transferred hand; TH). This phenomenon is known as intermanual transfer of learning. We explored specialization of brain activation underlying tool-use between hands by measuring regional cerebral blood flow in two monkeys using positron emission tomography. We found brain activation specified for TL in the bilateral prefrontal cortex, bilateral intraparietal sulcus region, and cerebellum contralateral to TH. The results suggest that those regions may be related to intermanual transfer of tool-use learning, presumably in terms of modifying a motor engram specific for OH.

Rapid learning of sequential tool use by macaque monkeys

Earlier reports have described monkeys in their natural habitat as being capable of purposefully using tools for activities such as obtaining food. However, little is known regarding the extent of macaque monkeys' ability to understand the functional meaning of objects as tools. We have trained Japanese macaques in tool-use behavior to demonstrate their abilities to solve stick problems involving the use of a novel tool and a sequential combination of different tools. Results suggest that macaque monkeys have cognitive abilities, such as (1). flexibility in applying previous experience in accordance with the requirements of the learning situation, (2). the foresight needed to conduct a series of acts in a continuous sequential manner and the ability to internally plan the necessary strategy.

Macaque prefrontal activity associated with extensive tool use

Macaques can utilize tools sequentially on a single object or they can modify functions effectively in a relevant context. Two Japanese macaques were scanned by positron emission tomography with H(2)15O during a tool combination task and two control tasks (single tool task and simple stick-waving task). In the tool combination task, monkeys were required to use two identical tools properly in different functions. We found increased activity in the bilateral prefrontal cortex (area 9/46), bilateral intraparietal sulcus regions, right cerebellum, and bilateral early visual cortices during the tool combination task with the right hand, compared with the single tool task. These results suggest that interactions between the fronto-cerebellar and the fronto-parietal circuit are responsible for appropriate and effective modifications of tools in their functions.

Tool-use learning induces BDNF expression in a selective portion of monkey anterior parietal cortex

Learning but not execution of tool-use induced expression of brain-derived neurotrophic factor (BDNF). The expression was highest in the anterior bank of the intraparietal sulcus, especially in the region posteriorly adjacent to the somatosensory shoulder and forearm region in area 3b, suggesting that BDNF plays a role in altering the body image of the hand to include the repeatedly used tool as its extension.

Increased synaptophysin expression through whisker stimulation in rat

1. Synaptophysin is responsible for the cycling of the synaptic vesicles containing the neurotransmitter, and it can be phosphorylated. 2. This study examined whether repeated whisker stimulation alters the expression of synaptophysin mRNA in the rat barrel cortex, and found induced expression of synaptophysin mRNA in the contralateral barrel cortex compared to that in the ipsilateral hemi sphere. 3. This result suggests that synaptophysin is involved in the modulation of the synaptic plasticity.

Self-images in the video monitor coded by monkey intraparietal neurons

When playing a video game, or using a teleoperator system, we feel our self-image projected into the video monitor as a part of or an extension of ourselves. Here we show that such a self image is coded by bimodal (somatosensory and visual) neurons in the monkey intraparietal cortex, which have visual receptive fields (RFs) encompassing their somatosensory RFs. We earlier showed these neurons to code the schema of the hand which can be altered in accordance with psychological modification of the body image; that is, when the monkey used a rake as a tool to extend its reach, the visual RFs of these neurons elongated along the axis of the tool, as if the monkey's self image extended to the end of the tool. In the present experiment, we trained monkeys to recognize their image in a video monitor (despite the earlier general belief that monkeys are not capable of doing so), and demonstrated that the visual RF of these bimodal neurons was now projected onto the video screen so as to code the image of the hand as an extension of the self. Further, the coding of the imaged hand could intentionally be altered to match the image artificially modified in the monitor.