Monica Maranesi

Neurons Controlling Voluntary Vocalization in the Macaque Ventral Premotor Cortex

The voluntary control of phonation is a crucial achievement in the evolution of speech. In humans, ventral premotor cortex (PMv) and Brocas area are known to be involved in voluntary phonation. In contrast, no neurophysiological data are available about the role of the oro-facial sector of nonhuman primates PMv in this function. In order to address this issue, we recorded PMv neurons from two monkeys trained to emit coo-calls. Results showed that a population of motor neurons specifically fire during vocalization. About two thirds of them discharged before sound onset, while the remaining were time-locked with it. The response of vocalization-selective neurons was present only during conditioned (voluntary) but not spontaneous (emotional) sound emission. These data suggest that the control of vocal production exerted by PMv neurons constitutes a newly emerging property in the monkey lineage, shedding light on the evolution of phonation-based communication from a nonhuman primate species.

Anatomo‐functional organization of the ventral primary motor and premotor cortex in the macaque monkey

The ventral agranular frontal cortex of the macaque monkey is formed by a mosaic of anatomically distinct areas. Although each area has been explored by several neurophysiological studies, most of them focused on small sectors of single areas, thus leaving to be clarified which is the general anatomo‐functional organization of this wide region. To fill this gap, we studied the ventral convexity of the frontal cortex in two macaque monkeys (Macaca nemestrina) using intracortical microstimulation and extracellular recording. Functional data were then matched with the cytoarchitectonic parcellation of the recorded region. The results demonstrated the existence of a dorso‐ventral functional border, encompassing the anatomical boundary between areas F4 and F1, and a rostro‐caudal anatomo‐functional border between areas F5 and F4. The ventral subdivision of areas F4 and F1 was highly electrically excitable, represented simple mouth movements and lacked visual properties; in contrast, their dorsal counterpart showed a higher stimulation threshold, represented forelimb and mouth motor acts and hosted different types of visual properties. The data also showed that area F5 was scarcely excitable, and displayed various motor specificity (e.g. for the type of grip) and complex visual (i.e. mirror responses) properties. Overall, the posterior areas F4 and F1 appear to be involved in organizing and controlling goal‐directed mouth motor acts and simple movements within different parts of the external (dorsal sector) and internal (ventral sector) space, whereas area F5 code motor acts at a more abstract level, thus enabling the emergence of higher order socio‐cognitive functions.

Application of floating silicon-based linear multielectrode arrays for acute recording of single neuron activity in awake behaving monkeys.

Abstract One of the fundamental challenges in behavioral neurophysiology in awake animals is the steady recording of action potentials of many single neurons for as long as possible. Here, we present single neuron data obtained during acute recordings mainly from premotor cortices of three macaque monkeys using a silicon-based linear multielectrode array. The most important aspect of these probes, compared with similar models commercially available, is that, once inserted into the brain using a dedicated insertion device providing an intermediate probe fixation by means of vacuum, they can be released and left floating in the brain. On the basis of our data, these features appear to provide (i) optimal physiological conditions for extracellular recordings, (ii) good or even excellent signal-to-noise ratio depending on the recorded brain area and cortical layer, and (iii) extreme stability of the signal over relatively long periods. The quality of the recorded signal did not change significantly after several penetrations into the same restricted cortical sector, suggesting limited tissue damage due to probe insertion. These results indicate that these probes offer several advantages for acute neurophysiological experiments in awake monkeys, and suggest the possibility to employ them for semichronic or even chronic studies.

Extending the Cortical Grasping Network: Pre-supplementary Motor Neuron Activity During Vision and Grasping of Objects

Grasping relies on a network of parieto-frontal areas lying on the dorsolateral and dorsomedial parts of the hemispheres. However, the initiation and sequencing of voluntary actions also requires the contribution of mesial premotor regions, particularly the pre-supplementary motor area F6. We recorded 233 F6 neurons from 2 monkeys with chronic linear multishank neural probes during reaching–grasping visuomotor tasks. We showed that F6 neurons play a role in the control of forelimb movements and some of them (26%) exhibit visual and/or motor specificity for the target object. Interestingly, area F6 neurons form 2 functionally distinct populations, showing either visually-triggered or movement-related bursts of activity, in contrast to the sustained visual-to-motor activity displayed by ventral premotor area F5 neurons recorded in the same animals and with the same task during previous studies. These findings suggest that F6 plays a role in object grasping and extend existing models of the cortical grasping network.

Versatile, modular 3D microelectrode arrays for neuronal ensemble recordings: from design to fabrication, assembly, and functional validation in non-human primates

OBJECTIVE Application-specific designs of electrode arrays offer an improved effectiveness for providing access to targeted brain regions in neuroscientific research and brain machine interfaces. The simultaneous and stable recording of neuronal ensembles is the main goal in the design of advanced neural interfaces. Here, we describe the development and assembly of highly customizable 3D microelectrode arrays and demonstrate their recording performance in chronic applications in non-human primates. APPROACH System assembly relies on a microfabricated stacking component that is combined with Michigan-style silicon-based electrode arrays interfacing highly flexible polyimide cables. Based on the novel stacking component, the lead time for implementing prototypes with altered electrode pitches is minimal. Once the fabrication and assembly accuracy of the stacked probes have been characterized, their recording performance is assessed during in vivo chronic experiments in awake rhesus macaques (Macaca mulatta) trained to execute reaching-grasping motor tasks. MAIN RESULTS Using a single set of fabrication tools, we implemented three variants of the stacking component for electrode distances of 250, 300 and 350 µm in the stacking direction. We assembled neural probes with up to 96 channels and an electrode density of 98 electrodes mm-2. Furthermore, we demonstrate that the shank alignment is accurate to a few µm at an angular alignment better than 1°. Three 64-channel probes were chronically implanted in two monkeys providing single-unit activity on more than 60% of all channels and excellent recording stability. Histological tissue sections, obtained 52 d after implantation from one of the monkeys, showed minimal tissue damage, in accordance with the high quality and stability of the recorded neural activity. SIGNIFICANCE The versatility of our fabrication and assembly approach should significantly support the development of ideal interface geometries for a broad spectrum of applications. With the demonstrated performance, these probes are suitable for both semi-chronic and chronic applications.

Spatial and viewpoint selectivity for others’ observed actions in monkey ventral premotor mirror neurons

The spatial location and viewpoint of observed actions are closely linked in natural social settings. For example, actions observed from a subjective viewpoint necessarily occur within the observer’s peripersonal space. Neurophysiological studies have shown that mirror neurons (MNs) of the monkey ventral premotor area F5 can code the spatial location of live observed actions. Furthermore, F5 MN discharge can also be modulated by the viewpoint from which filmed actions are seen. Nonetheless, whether and to what extent MNs can integrate viewpoint and spatial location of live observed actions remains unknown. We addressed this issue by comparing the activity of 148 F5 MNs while macaque monkeys observed an experimenter grasping in three different combinations of viewpoint and spatial location, namely, lateral view in the (1) extrapersonal and (2) peripersonal space and (3) subjective view in the peripersonal space. We found that the majority of MNs were space-selective (60.8%): those selective for the peripersonal space exhibited a preference for the subjective viewpoint both at the single-neuron and population level, whereas space-unselective neurons were view invariant. These findings reveal the existence of a previously neglected link between spatial and viewpoint selectivity in MN activity during live-action observation.

Cortical and subcortical connections of parietal and premotor nodes of the monkey hand mirror neuron network

Mirror neurons (MNs) are a class of cells originally discovered in the monkey ventral premotor cortex (PMv) and inferior parietal lobule (IPL). They discharge during both action execution and action observation and appear to play a crucial role in understanding others’ actions. It has been proposed that the mirror mechanism is based on a match between the visual description of actions, encoded in temporal cortical regions, and their motor representation, provided by PMv and IPL. However, neurons responding to action observation have been recently found in other cortical regions, suggesting that the mirror mechanism relies on a wider network. Here we provide the first description of this network by injecting neural tracers into physiologically identified IPL and PMv sectors containing hand MNs. Our results show that these sectors are reciprocally connected, in line with the current view, but IPL MN sectors showed virtually no direct connection with temporal visual areas. In addition, we found that PMv and IPL MN sectors share connections with several cortical regions, including the dorsal and mesial premotor cortex, the primary motor cortex, the secondary somatosensory cortex, the mid-dorsal insula and the ventrolateral prefrontal cortex, as well as subcortical structures, such as motor and polysensory thalamic nuclei and the mid-dorsal claustrum. We propose that each of these regions constitutes a node of an “extended network”, through which information relative to ongoing movements, social context, environmental contingencies, abstract rules, and internal states can influence MN activity and contribute to several socio-cognitive functions.

No need to match: a comment on Bach, Nicholson and Hudson's “Affordance-Matching Hypothesis”

Mirror neurons and canonical neurons are two classes of visuomotor neurons that are activated by different visual stimuli (Rizzolatti and Kalaska, 2012). Mirror neurons respond to a biological effector interacting with an object (Gallese et al., 1996), suggesting their role in action recognition, while canonical neurons respond to the presentation of a graspable object (Murata et al., 1997), and are considered crucial in visuomotor transformation for grasping (Jeannerod, 1995). In their interesting and thought-provoking “affordance-matching hypothesis” Bach et al. (2014) argue that both types of neurons contribute to action understanding. Action hypotheses are posited to be created by means of object affordances. Affordances are motor possibilities an object offers (Gibson, 1979). The visual description of an objects intrinsic features are associated with possible motor acts toward that object. A possible neural implementation for this mechanism are canonical neurons. The thus generated action hypothesis based on an object affordance would then be confirmed by the mirror neuron system. When a match between a predicted action (canonical) and an actually observed action (mirror neurons) is confirmed, either the action goal can be predicted based on observed behavior, or behavior can be predicted based on observed goals (see their Figure 1). We believe, however, that the proposed separation of hypothesis generation and hypothesis matching is not in line with the empirical evidence currently available, and that the division between “interpretation” and “prediction” relies on a cognitivist assumption that is hard to defend. We suggest that enactivist approaches provide a less problematic framework for studying action understanding. Bach and colleagues are not entirely explicit about the nature of the proposed matching mechanism between affordance and observed action, but we see two options for the proposed division of labor. In the first and admittedly unlikely option, mirror neurons play the role of a quizmaster that knows the answers. If the right hypothesis is posited, all the mirror neuron system has to do is confirm it. In this case, the contribution of the affordances is superfluous, as mirror neurons already extracted all that is needed from the perception of an action, (i.e., the quizmaster knows the answer). Counter evidence for this option exists in the form of mirror neurons that fire in the absence of an affordance to be matched. The auditory mirror neurons reported by Kohler et al. (2002) fire upon the presentation of the sound of an action alone (peanut breaking, paper tearing) without there being an affordance to match, or a prediction to confirm. But more importantly, virtually all mirror neuron studies (except Bonini et al., 2014a and Caggiano et al., 2009) involved actions performed in the extrapersonal space—out of reach for the monkey. Canonical neurons remain generally silent when an object is in extrapersonal space of the monkey, suggesting a mainly pragmatic (i.e., in terms of possibilities to interact with the object), rather than a metric reference frame (i.e., in terms of physical distance between the object and the observer; Maranesi et al., 2014). This means that the bulk of mirror neuron study reports mirror neuron firing in absence of canonical neuron firing. This, in turn, means that the major part of mirror neuron activity cannot rightfully be framed as “affordance matching,” at least not when canonical neurons are assumed to provide the affordances. The second and more likely option is that affordance extraction and mirror neuron firing jointly contribute to action understanding by each generating a hypothesis; one based on the object, consisting of one or more actions the object affords, and one about the action the actor is possibly performing (“action classification”; Uithol et al., 2011). When two hypotheses match, they are combined and the action is recognized. However, this means that mirror neuron input is not dependent on the availability of a to-be-matched affordance (i.e., mirror neuron activity is expected without affordances available), which is in line with the empirical evidence as highlighted above, but not predicted by the affordance-matching hypothesis. And also here the fact that canonical neurons fire upon object presentation only in monkeys peripersonal space would mean that canonical neuron-based affordances can only be matched within the monkeys peripersonal space. The only neurons showing canonical properties that could be activated by objects in the extrapersonal space are a recently discovered class of neurons reported by Bonini et al. (2014a). These neurons were dubbed “canonical-mirror neurons” as they show both canonical and mirror properties at the single neuron level. However, the canonical-mirror response to object presentation in the extra-personal space cannot be considered a neural implementation of an affordance, as these neurons do not fire for the same objects in the peripersonal space. Rather, these neurons seem to be involved in an object-triggered action prediction (Bonini et al., 2014a), which is indeed in line with the affordance-matching hypothesis, but emphatically does not generalize to canonical and mirror neurons in general. Additionally, recent findings (Bonini et al., 2014b) revealed that some mirror neurons, besides discharging during action observation, are also active when an action is not performed by an actor. This activation can obviously not be interpreted as a match between object affordances and action kinematics, as the latter are absent. As a solution, one might detach the hypothesis generation and confirmation processes from canonical and mirror neurons; the principle of affordance matching is after all not committed to these classes of neurons. But then we wonder what evidence remains for framing action understanding as “hypothesis generation and testing.” Why is there the need to combine the (in this case two) types of information into a unified representation? We believe that this framing of action understanding as drawing unified and coherent conclusions about observed actions may have been guided by the (cognitivist) assumption that cognition is centered around retrieving information. Alternatively, the framework of enactivism (Varela et al., 1991; Hutto, 2013; Hutto and Myin, 2013) seems to be much more in line with the complexity in action understanding. Enactivism assumes that cognition is not for creating representations about external events, but interacting with the world. In this framework, action understanding can take many guises of which many are best understood as a form of pattern completion: The observer is faced with an incomplete percept of an action, which is then completed based on perceptual mechanisms, mirror mechanisms and even higher associations—e.g., actors-object associations (see Uithol and Paulus, 2013). Importantly, there is no need to combine the different routes into a unified representation of the observed action or inferred action goal. If both object and action information are available, perhaps the classification or prediction process is faster, easier and better, but the current evidence suggest that unifying the types of information into a single match is not necessary. If action understanding is no longer framed as forming a conclusion about an observed action, but instead in terms of pluriform pattern completion that do not mount (always) to a unified representation, another assumption of the affordance matching hypothesis disappears as well: the difference between interpretation and prediction. Both interpretation (“classification” in our terminology) and prediction involve completing a pattern based on an incomplete percept. This means that the information flow cannot be segmented in “interpretation,” “knowledge,” and “prediction.” Interpretation is not a process upstream of knowledge, and prediction is not a process downstream from it, nor do they represent information flows in opposite directions; both notions refer to the process of sensorimotor action specification. In all, we believe that the suggestion of the affordance-matching hypothesis that different sources of information can each contribute to action understanding is an important one that could open doors to new lines of research. However, the current evidence does not support the proposed division between hypothesis-generation and hypothesis testing.