Area F5 Research Articles

Large Identified Pyramidal Cells in Macaque Motor and Premotor Cortex Exhibit “Thin Spikes”: Implications for Cell Type Classification

Recent studies have suggested that extracellular recordings of putative cortical interneurons have briefer spikes than those of pyramidal neurons, providing a means of identifying cortical cell types in recordings from awake monkeys. To test this, we investigated the spike duration of antidromically identified pyramidal tract neurons (PTNs) recorded from primary motor (M1) or ventral premotor cortex (area F5) in 4 awake macaque monkeys. M1 antidromic latencies (ADLs) were skewed toward short ADLs (151 PTNs; 0.5-5.5 ms, median 1.1 ms) and significantly different from that of F5 ADLs (54 PTNs; 1.0-6.9 ms, median 2.6 ms). The duration of PTN spikes, recorded with a high-pass filter of 300 Hz and measured from the negative trough to the positive peak of the spike waveform, ranged from 0.15 to 0.71 ms. Importantly, we found a positive linear correlation between ADL and spike duration in both M1 (R(2) = 0.40, p < 0.001) and F5 (R(2) = 0.57, p < 0.001). Thus PTNs with the shortest ADL (fastest axons) had the briefest spikes, and since PTN soma size is correlated with axon size and conduction velocity, it is likely that the largest pyramidal neurons (Betz cells in M1) have spikes with short durations (0.15-0.45 ms), which overlap heavily with those reported for putative interneurons in previous studies in non-primates. In summary, one class of physiologically identified cortical pyramidal neuron exhibits a wide variety of spike durations and the results suggest that spike duration alone may not be a reliable indicator of cell type.

Grasp Movement Decoding from Premotor and Parietal Cortex

Despite recent advances in harnessing cortical motor-related activity to control computer cursors and robotic devices, the ability to decode and execute different grasping patterns remains a major obstacle. Here we demonstrate a simple Bayesian decoder for real-time classification of grip type and wrist orientation in macaque monkeys that uses higher-order planning signals from anterior intraparietal cortex (AIP) and ventral premotor cortex (area F5). Real-time decoding was based on multiunit signals, which had similar tuning properties to cells in previous single-unit recording studies. Maximum decoding accuracy for two grasp types (power and precision grip) and five wrist orientations was 63% (chance level, 10%). Analysis of decoder performance showed that grip type decoding was highly accurate (90.6%), with most errors occurring during orientation classification. In a subsequent off-line analysis, we found small but significant performance improvements (mean, 6.25 percentage points) when using an optimized spike-sorting method (superparamagnetic clustering). Furthermore, we observed significant differences in the contributions of F5 and AIP for grasp decoding, with F5 being better suited for classification of the grip type and AIP contributing more toward decoding of object orientation. However, optimum decoding performance was maximal when using neural activity simultaneously from both areas. Overall, these results highlight quantitative differences in the functional representation of grasp movements in AIP and F5 and represent a first step toward using these signals for developing functional neural interfaces for hand grasping.

Anatomical Evidence for the Involvement of the Macaque Ventrolateral Prefrontal Area 12r in Controlling Goal-Directed Actions

The macaque ventrolateral prefrontal (VLPF) area 12r is thought to be involved in higher-order nonspatial information processing. We found that this area is connectionally heterogeneous, and the intermediate part is fully integrated in a cortical network involved in selecting and controlling object-oriented hand and mouth actions. Specifically, intermediate area 12r displayed dense connections with the caudal half of area 46v and orbitofrontal areas and relatively strong extraprefrontal connections involving the following: (1) the hand- and mouth-related ventral premotor area F5 and the anterior intraparietal (AIP) area, jointly involved in visuomotor transformations for grasping; (2) the SII sector that is connected to AIP and F5; (3) a sector of the inferotemporal area TEa/m, primarily corresponding to the sector densely connected to AIP; and (4) the insular and opercular frontal sectors, which are connected to AIP and F5. This connectivity pattern differed markedly from those of the caudal and rostral parts of area 12r. Caudal area 12r displayed dense connections with the caudal part of the VLPF, including oculomotor areas 8/FEF and 45B, relatively weak orbitofrontal connections and extraprefrontal connections limited to the inferotemporal cortex. Rostral area 12r displayed connections mostly with rostral prefrontal and orbitofrontal areas and relatively weaker connections with the fundus and the upper bank of the superior temporal sulcus. The present data suggest that the intermediate part of area 12r is involved in nonspatial information processing related to object properties and identity, for selecting and controlling goal-directed hand and mouth actions.

Ventral Premotor-Motor Cortex Interactions in the Macaque Monkey during Grasp: Response of Single Neurons to Intracortical Microstimulation

Recent stimulation studies in monkeys and humans have shown strong interactions between ventral premotor cortex (area F5) and the hand area of primary motor cortex (M1). These short-latency interactions usually involve facilitation from F5 of M1 outputs to hand muscles, although suppression has also been reported. This study, performed in three awake macaque monkeys, sought evidence that these interactions could be mediated by short-latency excitatory and inhibitory responses of single M1 neurons active during grasping tasks. We recorded responses of these M1 neurons to single low-threshold (≤40 μA) intracortical microstimuli delivered to F5 sites at which grasp-related neurons were recorded. In 29 sessions, we tested 232 M1 neurons with stimuli delivered to between one and four sites in F5. Of the 415 responses recorded, 142 (34%) showed significant effects. The most common type of response was pure excitation (53% of responses), with short latency (1.8-3.0 ms) and brief duration (∼1 ms); purely inhibitory responses had slightly longer latencies (2-5 ms) and were of small amplitude and longer duration (5-7 ms). They accounted for 13% of responses, whereas mixed excitation then inhibition was seen in 34%. Remarkably, a rather similar set of findings applied to 280 responses of 138 F5 neurons to M1 stimulation; 109 (34%) responses showed significant effects. Thus, with low-intensity stimuli, the dominant interaction between these two cortical areas is one of short-latency, brief excitation, most likely mediated by reciprocal F5-M1 connections. Some neurons were tested with stimuli at both 20 and 40 μA; inhibition tended to dominate at the higher intensity.

Grasping-Related Functional Magnetic Resonance Imaging Brain Responses in the Macaque Monkey

Research in recent decades has suggested the existence of a dedicated brain network devoted to the organization and execution of grasping, one of the most important and skilled movements of primates. Grasping an object requires the transformation of intrinsic object properties such as size, orientation, and shape into an appropriate motor scheme shaping the hand. Although electrophysiological recordings in the monkey model have proven invaluable for gaining insights into the neuronal substrate underlying this complex behavior, knowledge concerning the existence and organization of a similar system in the human brain is derived mainly from imaging studies. Here, we present for the first time functional magnetic resonance imaging (fMRI) of brain activity while macaque monkeys performed reaching and grasping movements in a 3 tesla MR scanner. Grasping in the dark (compared with reaching) yielded significant activations in anterior intraparietal area and ventral premotor area F5, in addition to area PFG in the rostral inferior parietal lobule, somatosensory areas (SI, SII, area 5), and the hand field of F1. Whole-brain macaque fMRI motor studies will be instrumental in establishing possible homologies concerning grasping organization in the human and monkey brains, bridging the gap between human imaging and monkey electrophysiology.

Decoding the activity of grasping neurons recorded from the ventral premotor area F5 of the macaque monkey

Many neurons in the monkey ventral premotor area F5 discharge selectively when the monkey grasps an object with a specific grip. Of these, the motor neurons are active only during grasping execution, whereas the visuomotor neurons also respond to object presentation. Here we assessed whether the activity of 90 task-related F5 neurons recorded from two macaque monkeys during the performance of a visually-guided grasping task can be used as input to pattern recognition algorithms aiming to decode different grips. The features exploited for the decoding were the mean firing rate and the mean interspike interval calculated over different time spans of the movement period (all neurons) or of the object presentation period (visuomotor neurons). A support vector machine (SVM) algorithm was applied to the neural activity recorded while the monkey grasped two sets of objects. The original set contained three objects that were grasped with different hand shapes, plus three others that were grasped with the same grip, whereas the six objects of the special set were grasped with six distinctive hand configurations. The algorithm predicted with accuracy greater than 95% all the distinct grips used to grasp the objects. The classification rate obtained using the first 25% of the movement period was 90%, whereas it was nearly perfect using the entire period. At least 16 neurons were needed for accurate performance, with a progressive increase in accuracy as more neurons were included. Classification errors revealed by confusion matrices were found to reflect similarities of hand grips used to grasp the objects. The use of visuomotor neurons' responses to object presentation yielded grip classification accuracy similar to that obtained from actual grasping execution. We suggest that F5 grasping-related activity might be used by neural prostheses to tailor hand shape to the specific object to be grasped even before movement onset.

Grasping Neurons of Monkey Parietal and Premotor Cortices Encode Action Goals at Distinct Levels of Abstraction during Complex Action Sequences

Natural actions are formed by distinct motor acts, each of which is endowed with its own motor purpose (i.e., grasping), chained together to attain the final action goal. Previous studies have shown that grasping neurons of parietal area PFG and premotor area F5 can code the goal of simple actions in which grasping is embedded. While during simple actions the target is usually visible, directly cueing the final goal, during complex action sequences is often concealed and has to be kept in mind to shape action unfolding. The aim of this study was to assess the relative contribution of sensory-cued or memory-driven information about the final goal to PFG and F5 grasping neurons activity. To this purpose, we trained two monkeys to perform complex action sequences, each including two successive grasping acts, aimed at specific final goals (eating or placing). We recorded 122 PFG and 89 F5 neurons. Forty-seven PFG and 26 F5 neurons displayed action goal selectivity only during the late phase of the action, when sensory information cueing the action goal became available. Reward contingency did not affect neuronal selectivity. Notably, 17 PFG neurons reflected the final goal from the early phase of action unfolding, when only memory-driven information was available. Crucially, when monkeys were prevented from obtaining such information before action onset, neurons lost their early selectivity. Our findings suggest that external sensory cues and individual's motor intention integrate at different level of abstraction within a large anatomo-functional network, encompassing parietal and premotor cortices.

A neural model for the visual tuning properties of action-selective neurons

AbstractSUMMARY: The recognition of actions of conspecifics is crucial for survival and social interaction. Most current models on the recognition of transitive (goal-directed) actions rely on the hypothesized role of internal motor simulations for action recognition. However, these models do not specify how visual information can be processed by cortical mechanisms in order to be compared with such motor representations. This raises the question how such visual processing might be accomplished, and in how far motor processing is critical in order to account for the visual properties of action-selective neurons.We present a neural model for the visual processing of transient actions that is consistent with physiological data and that accomplishes recognition of grasping actions from real video stimuli. Shape recognition is accomplished by a view-dependent hierarchical neural architecture that retains some coarse position information on the highest level that can be exploited by subsequent stages. Additionally, simple recurrent neural circuits integrate effector information over time and realize selectivity for temporal sequences. A novel mechanism combines information about the shape and position of object and effector in an object-centered frame of reference. Action-selective model neurons defined in such a relative reference frame are tuned to learned associations between object and effector shapes, as well as their relative position and motion.We demonstrate that this model reproduces a variety of electrophysiological findings on the visual properties of action-selective neurons in the superior temporal sulcus, and of mirror neurons in area F5. Specifically, the model accounts for the fact that a majority of mirror neurons in area F5 show view dependence. The model predicts a number of electrophysiological results, which partially could be confirmed in recent experiments.We conclude that the tuning of action-selective neurons given visual stimuli can be accounted for by well-established, predominantly visual neural processes rather than internal motor simulations. METHODS: The shape recognition relies on a hierarchy of feature detectors of increasing complexity and invariance [1]. The mid-level features are learned from sequences of gray-level images depicting segmented views of hand and object shapes. The highest hierarchy level consists of detector populations for complete shapes with a coarse spatial resolution of approximately 3.7°. Additionally, effector shapes are integrated over time by asymmetric lateral connections between shape detectors using a neural field approach [2]. These model neurons thus encode actions such as hand opening or closing for particular grip types.We exploit gain field mechanism in order to implement the central coordinate transformation of the shape representations to an object-centered reference frame [3]. Typical effector-object-interactions correspond to activity regions in such a relative reference frame and are learned from training examples. Similarly, simple motion-energy detectors are applied in the object-centered reference frame and encode relative motion. The properties of transitive action neurons are modeled as a multiplicative combination of relative shape and motion detectors. RESULTS: The model performance was tested on a set of 160 unsegmented sequences of hand grasping or placing actions performed on objects of different sizes, using different grip types and views. Hand actions and objects could be reliably recognized despite their mutual occlusions. Detectors on the highest level showed correct action tuning in more than 95% of the examples and generalized to untrained views.Furthermore, the model replicates a number of electrophysiological as well as imaging experiments on action-selective neurons, such as their particular selectivity for transitive actions compared to mimicked actions, the invariance to stimulus position, and their view-dependence. In particular, using the same stimulus set the model nicely fits neural data from a recent electrophysiological experiment that confirmed sequence selectivity in mirror neurons in area F5, as was predicted before by the model.

View-Based Encoding of Actions in Mirror Neurons of Area F5 in Macaque Premotor Cortex

Converging experimental evidence indicates that mirror neurons in the monkey premotor area F5 encode the goals of observed motor acts [1-3]. However, it is unknown whether they also contribute to encoding the perspective from which the motor acts of others are seen. In order to address this issue, we recorded the visual responses of mirror neurons of monkey area F5 by using a novel experimental paradigm based on the presentation of movies showing grasping motor acts from different visual perspectives. We found that the majority of the tested mirror neurons(74%) exhibited view-dependent activity with responses tuned to specific points of view. A minority of the tested mirror neurons (26%) exhibited view-independent responses. We conclude that view-independent mirror neurons encode action goals irrespective of the details of the observed motor acts, whereas the view-dependent ones might either form an intermediate step in the formation of view independence or contribute to a modulation of view-dependent representations in higher-level visual areas, potentially linking the goals of observed motor acts with their pictorial aspects.

Cortical connections of the anterior (F5a) subdivision of the macaque ventral premotor area F5

We traced the cortical connections of the anterior sector (F5a) of the macaque ventral premotor (PMv) area F5 and compared them with those of the adjacent F5 sectors, F5c and F5p. F5a displays a very dense "intrinsic" connectivity with F5c and F5p, premotor connections limited to F4 and F6/pre-SMA, relatively robust prefrontal connections with areas 46v and 12, and dense connections with rostral opercular frontal areas. Outside the frontal cortex, connections of F5a are dense with the SII region, relatively robust with inferior parietal areas PFG and AIP, weak with the inferior parietal area PF, and moderate with area 24. The comparison with data from injections in F5c and F5p showed that F5a, though sharing some common parietal connections with the other F5 sectors, displays several characterizing features providing robust evidence for its connectional distinctiveness. The present study provides evidence for a general organization of the PMv similar to that of the medial and dorsal premotor cortex, with F5a representing a pre-PMv area. Specifically, the present data suggest that F5a is a privileged site of integration, in the PMv, of parietal sensory-motor signals with higher-order information originating from prefrontal, rostral frontal opercular areas, and F6/pre-SMA. The results of this integration can be then broadcasted to the adjacent F5 sectors for the generation and control of hand actions and cognitive motor functions.

The mirror neuron system and treatment of stroke

Mirror neurons discharge during the execution of ecological goal-directed manual and oral actions, as well as during the observation of the same actions done by other individuals. These neurons were first identified in the ventral premotor cortex (PMv; area F5) and later on in the inferior parietal lobule (areas PF and PFG) of monkey brain, constituting a "mirror neuron" system. Several pieces of experimental data suggest that a mirror neuron system devoted to hand, mouth, and foot actions might also be present in humans. In the present paper, we review the experimental evidence on the role of the mirror neuron system in action understanding and imitation, both in hand motor function and speech. Based on the features of the mirror neuron system and its role in action understanding and imitation, we discuss the use of action observation and imitation as an approach for systematic training in the rehabilitation of patients with motor impairment of the upper limb and aphasia following stroke. We present the results of some preliminary studies to test this concept, and a discussion of network models as a measure of neurobiological change.

Context-Specific Grasp Movement Representation in Macaque Ventral Premotor Cortex

Hand grasping requires the transformation of sensory signals to hand movements. Neurons in area F5 (ventral premotor cortex) represent specific grasp movements (e.g., precision grip) as well as object features like orientation, and are involved in movement preparation and execution. Here, we examined how F5 neurons represent context-dependent grasping actions in macaques. We used a delayed grasping task in which animals grasped a handle either with a power or a precision grip depending on context information. Additionally, object orientation was varied to investigate how visual object features are integrated with context information. In 420 neurons from two animals, object orientation and grip type were equally encoded during the instruction epoch (27% and 26% of all cells, respectively). While orientation representation dropped during movement execution, grip type representation increased (20% vs 43%). According to tuning onset and offset, we classified neurons as sensory, sensorimotor, or motor. Grip type tuning was predominantly sensorimotor (28%) or motor (25%), whereas orientation-tuned cells were mainly sensory (11%) or sensorimotor (15%) and often also represented grip type (86%). Conversely, only 44% of grip-type tuned cells were also orientation-tuned. Furthermore, we found marked differences in the incidence of preferred conditions (power vs precision grips and middle vs extreme orientations) and in the anatomical distribution of the various cell classes. These results reveal important differences in how grip type and object orientation is processed in F5 and suggest that anatomically and functionally separable cell classes collaborate to generate hand grasping commands.

Human Anterior Intraparietal and Ventral Premotor Cortices Support Representations of Grasping with the Hand or a Novel Tool

Humans display a remarkable capacity to use tools instead of their biological effectors. Yet, little is known about the mechanisms that support these behaviors. Here, participants learned to grasp objects, appearing in a variety of orientations, with a novel, handheld mechanical tool. Following training, psychophysical functions relating grip preferences (i.e., pronated vs. supinated) to stimulus orientations indicate a reliance on distinct, effector-specific internal representations when planning grasping actions on the basis of the tool versus the hands. Accompanying fMRI data show that grip planning in both hand and tool conditions was associated with similar increases in activity within the same regions of the anterior intraparietal and caudal ventral premotor cortices, a putative homologue of the macaque anterior intraparietal-ventral premotor (area F5) "grasp circuit." These findings suggest that tool use is supported by effector-specific representations of grasping with the tool that are functionally independent of previously existing representations of the hand and yet occur within the same parieto-frontal regions involved in manual prehension. These levels of representation are critical for accurate planning and execution of actions in a manner that is sensitive to the respective properties of these effectors. These effector-specific representations likely coexist with effector-independent representations. The latter were recently reported in macaque F5 [Umiltà, M. A., Escola, L., Intskirveli, I., Grammont, F., Rochat, M., Caruana, F., et al. When pliers become fingers in the monkey motor system. Proceedings of the National Academy of Sciences, U.S.A., 105, 2209-2213, 2008] and appear to be established by tool use training through modification of existing representations of grasping with the hand. These more abstract levels of representation may facilitate the transfer of skills between hand and tool.

Responses of mirror neurons in area F5 to hand and tool grasping observation

Mirror neurons are a distinct class of neurons that discharge both during the execution of a motor act and during observation of the same or similar motor act performed by another individual. However, the extent to which mirror neurons coding a motor act with a specific goal (e.g., grasping) might also respond to the observation of a motor act having the same goal, but achieved with artificial effectors, is not yet established. In the present study, we addressed this issue by recording mirror neurons from the ventral premotor cortex (area F5) of two monkeys trained to grasp objects with pliers. Neuron activity was recorded during the observation and execution of grasping performed with the hand, with pliers and during observation of an experimenter spearing food with a stick. The results showed that virtually all neurons responding to the observation of hand grasping also responded to the observation of grasping with pliers and, many of them to the observation of spearing with a stick. However, the intensity and pattern of the response differed among conditions. Hand grasping observation determined the earliest and the strongest discharge, while pliers grasping and spearing observation triggered weaker responses at longer latencies. We conclude that F5 grasping mirror neurons respond to the observation of a family of stimuli leading to the same goal. However, the response pattern depends upon the similarity between the observed motor act and the one executed by the hand, the natural motor template.

Seeing other minds: attributed mental states influence perception

A current consensus views social perception as a bottom-up process in which the human brain uses social signals to make inferences about another's mental state. Here we propose that, contrary to this model, even the most basic perceptual processing of a social stimulus and closely associated automatic responses are modulated by mental-state attribution. We suggest that social perception is subserved by an interactive bidirectional relationship between the neural mechanisms supporting basic sensory processing of social information and the theory-of-mind system. Consequently, processing of a social stimulus cannot be divorced from its representation in terms of mental states. This hypothesis has far-reaching implications for our understanding of both the healthy social brain and characteristic social failures in psychopathology.

Projections of the hand field of the macaque ventral premotor area F5 to the brainstem and spinal cord

In the present study we first assessed that the hand motor field of the macaque ventral premotor area F5, involved in visuomotor control of hand actions, is connected to both the hand field of the primary motor cortex (M1) and the spinal cord. We then injected retroanterograde tracers in this field to completely illustrate its possible descending motor projections. In the brainstem the F5 hand motor field projects to the intermediate and deep layers of the superior colliculus (SC) and to sectors of the mesencephalic, pontine, and bulbar reticular formation, which are the sources of spinal projections. In the spinal cord, labeled terminals were virtually all confined to the C2-T1 segments, mostly contralaterally. At C6-T1 levels the labeling was weaker and mostly clustered laterally in the intermediate zone. At C2-C5 levels, labeled terminals were much denser and diffusely distributed over the mid-dorsal part of the intermediate zone where a propriospinal system that directly controls hand muscle motoneurons and mediates commands for the control of dexterous finger movements is located (Isa et al. [2007] Physiology 22:145-152). Thus, the F5 hand motor field has a weaker direct access and a stronger indirect access to spinal segments where hand muscle motoneurons are located, suggesting a role of this field in the generation and control of hand movements not only at the M1 level, but also at the spinal cord level. These projections may represent the neural substrate for the F5 hand motor field's role in the recovery of manual dexterity after M1 lesions.

Motor and non‐motor projections from the cerebellum to rostrocaudally distinct sectors of the dorsal premotor cortex in macaques

In the caudal part of the dorsal premotor cortex of macaques (area F2), both anatomical and physiological studies have identified two rostrocaudally separate sectors. The rostral sector (F2r) is located medial to the genu of the arcuate sulcus, and the caudal sector (F2c) is located lateral to the superior precentral dimple. Here we examined the sites of origin of projections from the cerebellum to F2r and F2c. We applied retrograde transsynaptic transport of a neurotropic virus, CVS-11 of rabies virus, in macaque monkeys. Three days after rabies injections into F2r or F2c, neuronal labeling was found in the deep cerebellar nuclei mainly of the contralateral hemisphere. After the F2r injection, labeled cells were distributed primarily in the caudoventral portion of the dentate nucleus, whereas cells labeled after the F2c injection were distributed in the rostrodorsal portion of the dentate nucleus, and in the interpositus and fastigial nuclei. Four days after rabies injections, Purkinje cells were densely labeled in the lateral part of the cerebellar cortex. After the F2r injection, Purkinje cell labeling was confined to Crus I and II, whereas the labeling seen after the F2c injection was located broadly from lobules III to VIII, including Crus I and II. These results have revealed that F2c receives inputs from broader areas of the cerebellum than F2r, and that distinct portions of the deep cerebellar nuclei and the cerebellar cortex send major projections to F2r and F2c, suggesting that F2c and F2r may be under specific influences of the cerebellum.

A neural model of the visual tuning properties of action-selective neurons in STS and area F5

A neural model of the visual tuning properties of action-selective neurons in STS and area F5

Cortical Connections of Parietal Field PEc in the Macaque: Linking Vision and Somatic Sensation for the Control of Limb Action

The cortical projections to the caudal part of the superior parietal lobule (area PEc) were studied in 6 cynomolgus monkeys using fluorescence tracers. Significant numbers of labeled cells were found in a restricted network of parietal, mesial, and frontal areas. Quantitative analysis demonstrated that approximately 30% of the total projection neurons originated in the adjacent areas of the dorsocaudal part of the superior parietal lobule (areas PE and V6A). The medial bank of the intraparietal sulcus, inferior parietal lobule, and frontal lobe (mainly the dorsocaudal part of premotor area F2) each contributed approximately 15% of the projection neurons. About 15% of the labeled neurons were located in the posterior cingulate area (PEci) and another 10% in other areas of the mesial surface of the hemisphere. Based on these data, we suggest that PEc processes information about the position of the limbs. The specific anatomical links between PEc and motor and premotor areas that host a representation of the lower limbs, together with the link with vestibular cortex and with areas involved in the analysis of optic flow and spatial navigation, imply a role for PEc in locomotion and coordinated limb movement in the environment.

Corticospinal Neurons in Macaque Ventral Premotor Cortex with Mirror Properties: A Potential Mechanism for Action Suppression?

SummaryThe discovery of “mirror neurons” in area F5 of the ventral premotor cortex has prompted many theories as to their possible function. However, the identity of mirror neurons remains unknown. Here, we investigated whether identified pyramidal tract neurons (PTNs) in area F5 of two adult macaques exhibited “mirror-like” activity. About half of the 64 PTNs tested showed significant modulation of their activity while monkeys observed precision grip of an object carried out by an experimenter, with somewhat fewer showing modulation during precision grip without an object or grasping concealed from the monkey. Therefore, mirror-like activity can be transmitted directly to the spinal cord via PTNs. A novel finding is that many PTNs (17/64) showed complete suppression of discharge during action observation, while firing actively when the monkey grasped food rewards. We speculate that this suppression of PTN discharge might be involved in the inhibition of self-movement during action observation.