Auditory and visual systems organization in Brodmann Area 8 for gaze-shift control: where we do not see, we can hear

Hearing is especially important for most primate species as they live in habitats of dense vegetation that limits vision. Stebbins (1980) summed up the evolution of the auditory system by assuming that earliest mammals exploited nocturnal niches since they were relatively free of many of the large, diurnal, predacious reptiles. Therefore, hearing and smell were more useful at night than vision. Our vision is limited not only in the dark but also outside the visual field. In fact, if we observe the behavior of a predator like a feline, oriented toward its prey, and at the same time a sound occurs behind, we might note three principal different behaviors: the predator could maintain its gaze and ears on the prey neglecting the sound source; the predator could maintain its gaze on the prey rotating ears and then shifting its auditory attention toward the sound source; finally the predator could break its attention and orient gaze and ears toward the sound source. A similar behavior is seen in human beings during social interaction with two or more interlocutors. In humans, orienting movements are carried out by the eyes, head, and/or body operating alone or in various combinations depending on the behavioral situation. However, in non-human primates, such as macaque monkeys, head orienting movements and, more generally, gaze-shift are accompanied by ear orienting movements, which allow the shifting of auditory attention toward a sound of interest (Bon and Lucchetti, 1994, 2006; Lucchetti et al., 2008; Lanzilotto et al., 2013; Yin, 2013). Considering all these assumptions, the auditory system could have an important role to detect information even from regions of the space that the visual system cannot explore without orienting movements. In other words, where we cannot see, we can hear. Through this opinion article, we argue that Brodmann Area 8 receives information from both auditory and visual systems and organizes a transformation of these sensory signals into gaze-shift motor commands. Our hypothesis is that this sensory-motor transformation is spatially organized, from both anatomical and functional points of view. Anatomical and functional properties of the Brodmann Area 8 (consisting in Area 8A plus Area 8B) support a medio-lateral organization for both auditory and visual systems. In particular, the lateral portion, corresponding to Area 8A or Frontal Eye Field (FEF), could play a role in receiving visual and auditory information from a central part of the visual field and then in organizing gaze-shift motor commands toward it. Otherwise, the medial portion, corresponding to Area 8B or Premotor Ear-Eye Field (PEEF), could play a role in receiving principally auditory information from a peripheral region of the space and then in organizing gaze-shift motor commands toward it

Evidence for a functional subdivision of Premotor Ear-Eye Field (Aera 8B)

The Supplementary EyeField (SEF) and the Frontal Eye Field (FEF) have been described as participating in gaze shift control. Recent evidence suggests, however, that other areas of the dorso medial prefrontal cortex also influence gaze shift. Herein, we haveinvestigated electrically evoked ear-and eye movements from the PremotorEar-Eye Field, or PEEF (area8B) of macaque monkeys. We stimulated PEEF during spontaneous condition (outside the task performance) and during the execution of a visual fixation task(VFT). In the first case, we functionally identified two regions within the PEEF: a core and a belt. In the core region, stimulation elicited forward ear movements; regarding the evoked eye movements, in some penetrations, stimulation elicited contraversive fixed-vectors with a mean amplitude of 5.14◦; while in other penetrations, we observed prevalently contralateral goal-directed eye movements having end-points that fell within15◦ inrespect to the primary eye position. On the contrary, in the belt region,stimulation elicited backward ear movements; regarding the eye movements, in some penetrations stimulation elicited prevalently contralateral goal-directed eye movements having end-points that fell within 15◦ in respect to the primary eye position, while in the lateral edge of the investigated region, stimulation elicited contralateral goal-directedey emovements having end-points that fell beyond 15◦in respect to the primary eye position. Stimulation during VFT either did not elicit eye movements or evoked saccades of only a few degrees. Finally, even though no head rotation movements were observed during the stimulation period, we viewed a relationship between the duration of stimulation and the neck forces exerted by the monkey’shead. We propose an updated vision of the PEEF composed of two functional regions, core and belt, which may beinvolved in integrating auditory and visual information important to the programming of gaze orienting movements

Self-assembling and charge transfer properties of thin organic films

2010/2011In the present thesis I dealt the issue of molecular ordering and charge transfer at two types of organic-inorganic interfaces that are representative of the basic constituents of an organic electron device. I investigated i.) the influence of a selected dielectric surface on the ordering of an overlayer of several organic molecules and ii.) the electronic transport properties of a single molecular junction with a metal electrode. Both systems have been characterized by a structural and electronic point of view. Among the techniques available for structural investigation, I made extensive use of Helium Atom Scattering (HAS) and Scanning Tunneling Microscopy (STM). The electronic properties, with particular emphasis to the charge transfer, have been addressed by two methods chosen according to the dimensionality of the system under consideration. For the charge transfer at laterally extended interfaces I used synchrotron based techniques, like Resonant Photoemssion Spectroscopy (RPES), while for the charge transport through a single molecule I used and developed the STM-based break junction technique (STM-BJ). For the first type of interface, I focused on the coupling between the TiO2(110)-1x1 surface and different organic semiconductor molecules: C60, pentacene, perylene-tetracarboxilic-acid-diimide (PTCDI) and perylene. The strong anisotropy of the substrate has been found to drive the adsorption geometry of the molecules leading to the formation of ordered phases (at least for the first layer). In particular pentacene, PTCDI and perylene (polycyclic aromatic hydrocarbons, PAHs) display a common self-assembly mechanism, where the molecules lay on the surface with their long axis oriented parallel to the [001] substrate direction. In the transverse direction [1-10] these molecules are observed to match the substrate periodicity by tilting the molecular plane around the long axis by an angle that depends on the molecular width. Nevertheless the molecule-to-substrate interaction is very weak as indicated by the molecular electronic structure, which is observed by X-ray spectroscopy to remain mostly unperturbed in the first molecular layer. Only PTCDI bears a major interaction with the TiO2(110)-1x1 surface, but confined to the molecular orbitals closest to the gap. The main experimental evidence of this interaction is the appearance of a new molecular filled state in the valence band region close to the Fermi level. By a combined RPES and NEXAFS study we have found that this new electronic state is due to the charge transfer occurring from the substrate Ti defect state (i.e. the excess of electrons associated with oxygen vacancies) to the lowest unoccupied molecular orbital (LUMO). For the second type of hybrid interface, instead, I exploited the nitrogen-link chemistry in order to bridge a phthalocyanine to two gold electrodes and to measure its conductance. In particular, by using the Tetraaza-Cu-Phthalocyanine I investigated the pyridine-gold bond that is relatively weak and insensitive to the local structure, a fundamental requirement for the establishment of well defined and stable transport properties. The weak interaction between the molecule and a representative metal electrode, namely the Au(100) surface, has been confirmed by spectroscopic and STM experiments. At RT the molecules have been found to diffuse on the surface and only at LT (55 K) they can be observed to self-organize into large molecular domains. On these domains, reliable and reproducible single molecule conductance measurements have been performed by using the STM-based break junction method. The conductance value obtained for the Tetraaza-Cu-Phthalocyanine (7x10-4 G0) has been rationalized in terms of the molecular length and degree of conjugation, as well as by correlation to the energy level alignment at the junction.XXIV Ciclo198

From Observed Action Identity to Social Affordances

Others' observed actions cause continuously changing retinal images, making it challenging to build neural representations of action identity. The monkey anterior intraparietal area (AIP) and its putative human homologue (phAIP) host neurons selective for observed manipulative actions (OMAs). The neuronal activity of both AIP and phAIP allows a stable readout of OMA identity across visual formats, but human neurons exhibit greater invariance and generalize from observed actions to action verbs. These properties stem from the convergence in AIP of superior temporal signals concerning: (i) observed body movements; and (ii) the changes in the body-object relationship. We propose that evolutionarily preserved mechanisms underlie the specification of observed-actions identity and the selection of motor responses afforded by them, thereby promoting social behavior

Chronic neural probe for simultaneous recording of single-unit, multi-unit, and local field potential activity from multiple brain sites

Drug resistant focal epilepsy can be treated by resecting the epileptic focus requiring a precise focus localization using stereoelectroencephalography (SEEG) probes. As commercial SEEG probes offer only a limited spatial resolution, probes of higher channel count and design freedom enabling the incorporation of macro and microelectrodes would help increasing spatial resolution and thus open new perspectives for investigating mechanisms underlying focal epilepsy and its treatment. This work describes a new fabrication process for SEEG probes with materials and dimensions similar to clinical probes enabling recording single neuron activity at high spatial resolution. Polyimide is used as a biocompatible flexible substrate into which platinum electrodes and leads are... The resulting probe features match those of clinically approved devices. Tests in saline solution confirmed the probe stability and functionality. Probes were implanted into the brain of one monkey (Macaca mulatta), trained to perform different motor tasks. Suitable configurations including up to 128 electrode sites allow the recording of task-related neuronal signals. Probes with 32 and 64 electrode sites were implanted in the posterior parietal cortex. Local field potentials and multi-unit activity were recorded as early as one hour after implantation. Stable single-unit activity was achieved for up to 26 days after implantation of a 64-channel probe. All recorded signals showed modulation during task execution. With the novel probes it is possible to record stable biologically relevant data over a time span exceeding the usual time needed for epileptic focus localization in human patients. This is the first time that single units are recorded along cylindrical polyimide probes chronically implanted 22 mm deep into the brain of a monkey, which suggests the potential usefulness of this probe for human applications

The porphyrin triplet state : from porphyrin-2,2':6',2''-terpyridine conjugates to photocatalysis

The doctoral work we present consists of three separate parts, each dealing with a different project, each is linked to the others by a main theme: porphyrins. Part I is relative to the synthesis of a new porphyrin-terpyridine conjugate and its application in the preparation of homo- and heteroleptic transition metal complexes. Particularly, attention is focused on a heteroleptic ruthenium complex, which was tested as a light harvester in regards to dye-sensitized solar cell applications. Homoleptic complexes were prepared to study their spectroelectrochemical behaviour. Part II moves the focus onto photocatalysis. A water-soluble free-base porphyrin catalyst has been prepared and employed to sensitize molecular oxygen to its singlet state. Singlet oxygen is active against a wide selection of substrates, among which we decided to work on two: thiols and sulfides. Studies against simple aminoacids made us interested in assessing whether photocatalytic activity would be retained in polypeptides in vitro. We stepped into photodynamic therapy by applying our photocatalyst to E. coli liquid cultures and following the population change over exposure to singlet oxygen. From a pure synthetic point of view, we screened the photocatalyst on aliphatic and aromatic sulfides. We collected examples on commercial substrates, both symmetric and asymmetric, of natural or pharmaceutical origin. The main goals were the assessment of catalyst’s site-specificity, tolerance to coexisting functional groups and action on diverse structures. Part III arises from a purely academic interest: is it possible to record the emission spectrum of a redox species, electrochemically generated in situ? In fact, spectroelectrochemistry is widely applied to absorption spectroscopy, where detection of the transmitted light greatly increases sensitivity. It is indeed possible to record such a signal, with the main problem being that reduced or oxidized species mainly show quenching of the emission. For a reversible redox couple, reversing the potential results in the recovery of the original fluorescence band. It remains a challenge to find a molecule whose redox behaviour is associated with emission at different wavelengths or variation in the vibrational pattern of the emission band

Neuronal Encoding of Self and Others' Head Rotation in the Macaque Dorsal Prefrontal Cortex.

Following gaze is a crucial skill, in primates, for understanding where and at what others are looking, and often requires head rotation. The neural basis underlying head rotation are deemed to overlap with the parieto-frontal attention/gaze-shift network. Here, we show that a set of neurons in monkey's Brodmann area 9/46dr (BA 9/46dr), which is involved in orienting processes and joint attention, becomes active during self head rotation and that the activity of these neurons cannot be accounted for by saccade-related activity (head-rotation neurons). Another set of BA 9/46dr neurons encodes head rotation performed by an observed agent facing the monkey (visually triggered neurons). Among these latter neurons, almost half exhibit the intriguing property of encoding both execution and observation of head rotation (mirror-like neurons). Finally, by means of neuronal tracing techniques, we showed that BA 9/46dr takes part into two distinct networks: a dorso/mesial network, playing a role in spatial head/gaze orientation, and a ventrolateral network, likely involved in processing social stimuli and mirroring others' head. The overall results of this study provide a new, comprehensive picture of the role of BA 9/46dr in encoding self and others' head rotation, likely playing a role in head-following behaviors

Largely shared neural codes for biological and nonbiological observed movements but not for executed actions in monkey premotor areas

The neural processing of others' observed actions recruits a large network of brain regions (the action observation network; AON) in which frontal motor areas are thought to play a crucial role. As the discovery of mirror neurons (MNs) in the ventral premotor cortex, it has been assumed that their activation was conditional upon the presentation of biological rather than nonbiological motion stimuli, supporting a form of direct visuomotor matching. Nonetheless, nonbiological observed movements have rarely been used as control stimuli to evaluate visual specificity, thereby leaving the issue of similarity among neural codes for executed actions and biological or nonbiological observed movements unresolved. Here, we addressed this issue by recording from two nodes of the AON that are attracting increasing interest, namely, the ventrorostral part of the dorsal premotor area F2 and the mesial presupplementary motor area F6 of macaques while they 1) executed a reaching-grasping task, 2) observed an experimenter performing the task, and 3) observed a nonbiological effector moving in the same context. Our findings revealed stronger neuronal responses to the observation of biological than nonbiological movement, but biological and nonbiological visual stimuli produced highly similar neural dynamics and relied on largely shared neural codes, which in turn remarkably differed from those associated with executed actions. These results indicate that, in highly familiar contexts, visuomotor remapping processes in premotor areas hosting MNs are more complex and flexible than predicted by a direct visuomotor matching hypothesis