Evaluation of Motor Imagery-Based BCI methods in neurorehabilitation of Parkinson's Disease patients.

The study reports the performance of Parkinson's disease (PD) patients to operate Motor-Imagery based Brain-Computer Interface (MI-BCI) and compares three selected pre-processing and classification approaches. The experiment was conducted on 7 PD patients who performed a total of 14 MI-BCI sessions targeting lower extremities. EEG was recorded during the initial calibration phase of each session, and the specific BCI models were produced by using Spectrally weighted Common Spatial Patterns (SpecCSP), Source Power Comodulation (SPoC) and Filter-Bank Common Spatial Patterns (FBCSP) methods. The results showed that FBCSP outperformed SPoC in terms of accuracy, and both SPoC and SpecCSP in terms of the false-positive ratio. The study also demonstrates that PD patients were capable of operating MI-BCI, although with lower accuracy.

Transcranial magnetic stimulation in developmental stuttering: Relations with previous neurophysiological research and future perspectives.

Developmental stuttering (DS) is a disruption of the rhythm of speech, and affected people may be unable to execute fluent voluntary speech. There are still questions about the exact causes of DS. Evidence suggests there are differences in the structure and functioning of motor systems used for preparing, executing, and controlling motor acts, especially when they are speech related. Much research has been obtained using neuroimaging methods, ranging from functional magnetic resonance to diffusion tensor imaging and electroencephalography/magnetoencephalography. Studies using transcranial magnetic stimulation (TMS) in DS have been uncommon until recently. This is surprising considering the relationship between the functionality of the motor system and DS, and the wide use of TMS in motor-related disturbances such as Parkinson's Disease, Tourette's Syndrome, and dystonia. Consequently, TMS could shed further light on motor aspects of DS. The present work aims to investigate the use of TMS for understanding DS neural mechanisms by reviewing TMS papers in the DS field. Until now, TMS has contributed to the understanding of the excitatory/inhibitory ratio of DS motor functioning, also helping to better understand and critically review evidence about stuttering mechanisms obtained from different techniques, which allowed the investigation of cortico-basal-thalamo-cortical and white matter/connection dysfunctions.

EEG dynamics of the frontoparietal network during reaching preparation in humans.

Visuomotor transformation processes are essential when accurate reaching movements towards a visual target have to be performed. In contrast, those transformations are not needed for similar, but non-visually guided, arm movements. According to previous studies, these transformations are carried out by neuronal populations located in the parietal and frontal cortical areas (the so-called "dorsal visual stream"). However, it is still debated whether these processes are mediated by the sequential and/or parallel activation of the frontoparietal areas. To investigate this issue, we designed a task where the same visual cue could represent either the target of a reaching/pointing movement or the go-signal for a similar but non-targeting arm movement. By subtracting the event-related potentials (ERPs) recorded from healthy subjects performing the two conditions, we identified the brain processes underlying the visuomotor transformations needed for accurate reaching/pointing movements. We then localized the generators by means of cortical current density (CCD) reconstruction and studied their dynamics from visual cue presentation to movement onset. The results showed simultaneous activation of the parietal and frontal areas from 140 to 260 ms. The results are interpreted as neural correlates of two critical phases of visuomotor integration, namely target selection and movement selection. Our findings suggest that the visuomotor transformation processes required for correct reaching/pointing movements do not rely on a purely sequential activation of the frontoparietal areas, but mainly on a parallel information processing system, where feedback circuits play an important role before movement onset.

Visual representation of space in congenital and acquired strabismus.

The aim of the present work was to readdress the problem of altered spatial localization in strabismic subjects and to assess whether and how spatial representation is affected by the degree of plasticity of the brain. We therefore compared targeting performance in adult subjects affected by acquired strabismus versus children affected by congenital strabismus. Our data confirm the correlation between deviation of the eye and targeting errors, but they also show that this correlation is not present when strabismus occurs early in life. We suggest that the neuronal machinery involved in the building of an internal representation of space reaches its full maturity several years after birth and that this might explain the limited differences observed in targeting errors between normal and strabismic children.

Arm movement-related neurons in the visual area V6A of the macaque superior parietal lobule.

Area V6A is a cortical visual area located in the posterior face of the superior parietal lobule in the macaque monkey. It contains visual neurons as well as neurons not activated by any kind of visual stimulation. The aim of this study was to look for possible features able to activate these latter neurons. We tested 70 non-visual V6A neurons. Forty-three of them showed an arm movement-related neural discharge due to somatosensory stimulation and/or skeletomotor activity of the upper limbs of the animal. The arm movement-related neural discharge started before the onset of arm movement, often before the earliest electromyographic activity. Thus, although the discharge is probably supported by proprioceptive and tactile inputs it is not fully dependent on them. Arm movement-related neurons of area V6A seem to be well equipped for integrating motor signals related to arm movements with somatosensory signals evoked by those movements. Taking into account also the visual characteristics of V6A neurons, it seems likely that area V6A as a whole is involved in the visual guiding of reaching.

Cortical mechanisms for visual perception of object motion and position in space.

The present review is aimed at analyzing and discussing some of the cortical mechanisms possibly involved in the perception of object motion and object localization in the visual field. A comprehensive approach to these topics would be beyond the scope of this work. The highest priority, therefore, will be given to the cortical machinery involved in these processes, while very little (or nothing at all) will be said on the possible role played by subcortical structures such as the lateral geniculate nucleus and the superior colliculus which, albeit not directly involved in perception, might contribute to it.

Functional demarcation of a border between areas V6 and V6A in the superior parietal gyrus of the macaque monkey.

We have compared physiological data recorded from three alert macaque monkeys with separate observations of local connectivity, to locate and characterize the functional border between two related but distinct visual areas on the caudal face of the superior parietal gyrus. We refer to these areas as V6 and V6A. The occupy almost the entire extent of the anterior bank of the parieto-occipital sulcus, V6A being the more dorsal. These two areas are strongly interconnected. Anatomically, we have defined the border as the point at which labelled axon terminals first adopt a recognizably 'descending' pattern in their laminar characteristics, after injections of wheatgerm agglutinin-horseradish peroxidase into the dorsal half of the gyrus (in presumptive V6A). A similar principle was used to recognize the same border by the pattern of input from area V5, except that in this case the relevant transition in laminar characteristics is that between an 'intermediate' pattern (in V6) and an 'ascending' pattern (in V6A). V6A was found to be distinct from V6 in a number of its physiological properties. Unlike V6, it contains visually unresponsive cells as well as units with craniotopic receptive fields ('real-position' cells), units tuned to very slow stimulus speeds, units with complex visual selectivities and units with activity related to attention. V6A was also found to have a larger mean receptive field size and scatter than V6. By contrast, response properties related to the basic orientation and direction of moving bar stimuli were indistinguishable between V6 and V6A, as was the influence of gaze direction on cell activity in the two areas. Two-dimensional maps of the recording sites allowed reconstruction of the V6/V6A border. For comparison, the anatomical results were rendered on two-dimensional maps of identical format to those used to summarize the physiological data. After normalizing for relative size, the physiological and connectional estimates of the border between V6 and V6A were found to coincide, at least within the range of individual variation between hemispheres. An architectonic map in the same format was also made from a hemisphere stained for myelin and Nissl substance. Area PO, defined by its general density of myelination was not distinct in this material, but several architectural features were traceable and one of these was also found to approximate the V6/V6A border. The particular criteria that distinguish V6 from V6A differ from a recent description of areas PO and POd in the Cebus monkey; we believe it most likely that PO and POd together may correspond to V6.

Eye position influence on the parieto-occipital area PO (V6) of the macaque monkey.

The aim of this work was to study the effect of eye position on the activity of neurons of area PO (V6), a cortical region located in the most posterior part of the superior parietal lobule. Experiments were carried out on three awake macaque monkeys. Animals sat in a primate chair in front of a large screen, and fixated a small spot of light projected in different screen locations while the activity of single neurons was extracellularly recorded. Both visual and non-visual neurons were found. About 48% of visual and 32% of non-visual neurons showed eye position-related activity in total darkness, while in approximately 61% of visual response was modulated by eye position in the orbit. Eye position fields and/or gain fields were different from cell to cell, going from large and quite planar fields up to peak-shaped fields localized in more or less restricted regions of the animal's field of view. The spatial distribution of fixation point locations evoking peak activity in the eye position-sensitive population did not show any evident laterality effect, or significant top/bottom asymmetry. Moreover, the cortical distribution of eye position-sensitive neurons was quite uniform all over the cortical region studied, suggesting the absence of segregation for this property within area PO (V6). In the great majority of visual neurons, the receptive field 'moved' with gaze according to eye displacements, remaining at the same retinotopic coordinates, as is usual for visual neurons. In some cases, the receptive field did not move with gaze, remaining anchored to the same spatial location regardless of eye movements ('real-position cells'). A model is proposed suggesting how eye position-sensitive visual neurons might build up real-position cells in local networks within area PO (V6). The presence in area PO (V6) of real-position cells together with a high percentage of eye position-sensitive neurons, most of them visual in nature, suggests that this cortical area is engaged in the spatial encoding of extrapersonal visual space. Since lesions of the superior parietal lobule in humans produce deficits in visual localization of targets as well as in arm-reaching for them, and taking into account that the monkey's area PO (V6) is reported to be connected with the premotor area 6, we suggest that area PO (V6) supplies the premotor cortex with the visuo-spatial information required for the visual control of arm-reaching movements.

Functional properties of neurons in area V1 of awake macaque monkeys: peripheral versus central visual field representation.

The region of the striate cortex where the visual field is represented up to 52 degrees from the fovea was explored in awake, behaving monkeys. Extracellular recordings were made from 241 neurons. On the basis of their receptive field position in the visual field, they were subdivided into a central (within 10 degrees from the fovea) and a peripheral (beyond 10 degrees) group. Sensitivity to orientation, length, direction and velocity of movement of conventional light stimuli was tested and compared in the two samples. Besides the well-known increase of receptive field size with eccentricity, gross differences were found only for the sensitivity to the velocity of stimulus movement. The great majority of neurons in the central sample preferred slow velocities and showed no sensitivity to velocities above 100 degrees/sec. In contrast, many peripheral neurons were poorly sensitive to slow speeds of movement and well responsive to high velocities, above 100 degrees/sec. Cells that showed a better response to an actual stimulus movement in the visual field than to a retinal image movement self-induced by an eye-movement ("real-motion" cells) were also searched for in the two samples. They were found in the 13% of the central neurons and in the 25% of the peripheral neurons. Present data extend to the awake, behaving animal what already known from paralysed animal, indicating that in physiological conditions central and peripheral vision have a different functional role in the analysis of motion within the visual field.

Visuomotor reconstruction of visual space.

The existence of an internal representation of visual space can be demonstrated by observing the ability to reconstruct different spatial locations in absence of visual object still indicating those positions. The characteristics of this spatial map were investigated in healthy human subjects instructed to point to different spatial positions previously indicated by a visual objects which disappeared. Pointings were made with different delays from the disappearance of the peripheral visual target and with different permanence time of it. The idea emerging from this study of the internal representation of visual space is that it is distorted, with the lower hemifield overestimated with respect to the upper one. Moreover, this map slowly deteriorates with time and its precision depends on the time during which the object can be observed.

Parietal neurons encoding spatial locations in craniotopic coordinates.

The receptive fields of visual neurons are known to be retinotopically arranged, and in awake animals they "move" with gaze, maintaining the same retinotopic location regardless of eye position. Here, we report the existence in the monkey parietal cortex of cells (called "real-position" cells) whose receptive field does not systematically move with gaze. These cells respond to the visual stimulation of the same spatial location regardless of eye position and therefore directly encode visual space in craniotopic instead of retinotopic coordinates.

Parietal neurons encoding visual space in a head-frame of reference.

Neurons of the visual system are known to have receptive fields organized in retinotopic coordinates. We wanted to test whether visual neurons existed whose receptive fields were organized in spatial coordinates. Extracellular recordings from single cells were carried out in one area of the posterior parietal cortex (area V6) of a behaving macaque monkey. Among a great majority of retinotopically organized visual cells, neurons whose visual receptive field did not shift with gaze were also found. These cells responded to the visual stimulation of the same spatial position independently of the animal's direction of gaze, that is, their receptive field was anchored to an absolute spatial location. We suggest that these neurons directly encode visual space and are involved in programming visually-guided motor actions in space.

Functional Properties of Neurons in the Anterior Bank of the Parieto-occipital Sulcus of the Macaque Monkey.

Extracellular recordings were made in the anterior bank of the parieto-occipital sulcus of two waking monkeys trained to perform fixation tasks in normal illumination or in complete darkness. Of the recorded neurons, 73% (251/343) were responsive to visual stimulation, but their overall organization did not conform to a simple, continuous retinotopic map. Most of the visual neurons showed a high degree of orientation and direction sensitivity, higher than that found in areas V1, V2 and V3A under the same experimental conditions. Whether they had a resolvable receptive field or not, the discharge rate of many neurons in the anterior bank of the parieto-occipital sulcus was influenced by oculomotor activity. The animals were required to execute pursuit or saccadic eye movements in darkness. Saccadic eye movements were found to influence 19% of the neurons tested (29/156); by contrast, pursuit eye movements were without effect (0/64). Saccade responses were direction-tuned and, in several cases, the neuronal discharge started before the onset of eye movement. The animals were also required to gaze, in darkness, at nine different positions on the screen they faced. Of the neurons tested, 59% (102/174) were affected by the direction of gaze. Higher discharge rates were generally observed when the animals looked towards the lower part of the field of view. Given the functional properties of its neurons, its connections with area V3A-where neural signals appropriate for building an objective map of the visual space are present (Galletti and Battaglini, 1989, J. Neurosci., 9, 1112-1125)-and its output to the visuomotor centres involved in the generation of saccades (frontal eye fields and superior colliculus), we infer that the cortex of the anterior bank of the parieto-occipital sulcus might be part of the network involved in the control of gaze in order to locate objects in visual space.

Source of the eye-movement signal reaching real-motion cells.

The stability of visual perception despite eye movements suggests the existence in the visual system of neurons able to recognize whether the movement of a retinal image is due to the actual movement of an object or is self-induced by the ocular movement. We found neurons of this type in several areas of the monkey visual cortex and named them "real-motion" cells. Extracellular recordings were carried out from single neurons of the cortical prestriate area V3A of two awake macaque monkeys. Eighty-seven neurons were studied by comparing their responses during stimulus movement across the stationary receptive field, and receptive-field movement across the stationary stimulus. This visual stimulation was presented against a uniform visual background, in darkness or against a textured background. Neurons which were not real-motion in light (45/87) maintained their behaviour in darkness, while about 40% of real-motion cells lost this behaviour in darkness. Both real-motion and non real-motion cells maintained the same behaviour when tested against a uniform or textured visual background but often, texture increased the difference in the response that real-motion cells showed between stimulus and eye movement. These data suggest that the eye-movement signal which reaches real-motion cells and is responsible for their behaviour may be either retinal or extraretinal in nature. This double innervation is in good agreement with perceptual phenomena related to the detection of movement in the visual field.

'Real-motion' cells in area V3A of macaque visual cortex.

The stability of visual perception despite eye movements suggests the existence, in the visual system, of neural elements able to recognize whether a movement of an image occurring in a particular part of the retina is the consequence of an actual movement that occurred in the visual field, or self-induced by an ocular movement while the object was still in the field of view. Recordings from single neurons in area V3A of awake macaque monkeys were made to check the existence of such a type of neurons (called 'real-motion' cells; see Galletti et al. 1984, 1988) in this prestriate area of the visual cortex. A total of 119 neurons were recorded from area V3A. They were highly sensitive to the orientation of the visual stimuli, being on average more sensitive than V1 and V2 neurons. Almost all of them were sensitive to a large range of velocities of stimulus movement and about one half to the direction of it. In order to assess whether they gave different responses to the movement of a stimulus and to that of its retinal image alone (self-induced by an eye movement while the stimulus was still), a comparison was made between neuronal responses obtained when a moving stimulus swept a stationary receptive field (during steady fixation) and when a moving receptive field swept a stationary stimulus (during tracking eye movement). The receptive field stimulation at retinal level was physically the same in both cases, but only in the first was there actual movement of the visual stimulus. Control trials, where the monkeys performed tracking eye movements without any intentional receptive field stimulation, were also carried out. For a number of neurons, the test was repeated in darkness and against a textured visual background. Eighty-seven neurons were fully studied to assess whether they were real-motion cells. About 48% of them (42/87) showed significant differences between responses to stimulus versus eye movement. The great majority of these cells (36/42) were real-motion cells, in that they showed a weaker response to visual stimulation during tracking than to the actual stimulus movement during steady fixation. On average, the reduction in visual response during eye movement was 64.0 +/- 15.7% (SD).(ABSTRACT TRUNCATED AT 400 WORDS)

Gaze-dependent visual neurons in area V3A of monkey prestriate cortex.

Extracellular recordings from single neurons of the prestriate area V3A were carried out in awake, behaving monkeys, to test the influence of the direction of gaze on cellular activity. The responsiveness to visual stimulation of about half of the studied neurons (88/187) was influenced by the animal's direction of gaze: physically identical visual stimuli delivered to identical retinotopic positions (on the receptive field) evoked different responses, depending upon the direction of gaze. Control experiments discount the possibility that the observed phenomenon was due to changes in visual background or in depth, depending on the direction in which the animal was looking. The gaze effect modulated cell excitability with different strengths for different gaze directions. The majority of these neurons were more responsive when the animal looked contralaterally with respect to the hemisphere they were recorded from. Gaze-dependent neurons seem to be segregated in restricted cortical regions, within area V3A, without mixing with non-gaze-dependent cells of the same cortical area. The most reliable differences between V3A gaze-dependent neurons and the same type of cells previously described in area 7a (Andersen and Mountcastle, 1983) concern the small receptive field size, the laterality of gaze effect, and the lack of straight-ahead facilitated or inhibited neurons in area V3A. Since the present results show that V3A gaze-dependent neurons combine information about the position of the eye in the orbit with that of a restricted retinal locus (their receptive field), we suggest that they might directly encode spatial locations of the animal's field of view in a head frame of reference. These cells might be involved in the construction of an internal map of the visual environment in which the topographical position of the objects reflects their objective position in space instead of reflecting the retinotopic position of their images. Such an objective map of the visual world might allow the stability of visual perception despite eye movement.

'Real-motion' cells in visual area V2 of behaving macaque monkeys.

Extracellular recordings were made in area V2 of behaving macaque monkeys. Neurons were classified into three groups: non-oriented cells, oriented cells with antagonistic areas and oriented cells without antagonistic areas in their receptive field. All neurons were tested with standard visual stimulations in order to assess whether they gave different responses to the movement of a stimulus and to the movement of its retinal image alone, when the stimulus was motionless and the animal voluntarily moved its eyes. To do this, neuronal responses obtained when a moving stimulus swept a stationary receptive field (during steady fixation) and when a moving receptive field swept a stationary stimulus (during tracking eye movements), were compared. The receptive field stimulation at retinal level was physically the same in both cases, but only in the first was there actual movement of the visual stimulus. Control trials, where the monkeys performed tracking eye movements without any intentional receptive field stimulation, were also carried out. Out of a total of 263 neurons isolated in the central 10 deg representation of area V2, 101 were fully studied with the visual stimulation described above. Most of these (83/101; 82%) gave about the same response to the two situations. About 14% (14/101) gave a good response to stimulus movements during steady fixation and a very weak one to retinal image displacements of stationary stimuli during visual tracking. We have called neurons of this type "real-motion cells" (cf. Galletti et al. 1984). None of the non-oriented cells was a real-motion one, while about an equal percentage of real-motion cells was found among the oriented cells with and without antagonistic areas. Finally, we found only 4 neurons which showed behaviour opposite to that of real-motion cells, i.e. they showed a better response to displacement of the retinal image of stationary stimuli than to actual movement of stimuli. We suggest that real-motion cells might contribute to correctly evaluating movement in the visual field in spite of eye movements and that they might allow recognition of the movement of an object even if it moves across a non-patterned visual background. Present data on area V2, together with similar results observed in area V1 (Galletti et al. 1984; Battaglini et al. 1986), support the view that these two cortical areas analyse the movement in a parallel fashion along with many other characteristics of the visual stimulus.

Effect of fast moving stimuli and saccadic eye movements on cell activity in visual areas V1 and V2 of behaving monkeys.

Extracellular recordings were carried out in the visual cortex of behaving monkeys trained on a fixation/detection task, during which a target light was displayed stationary or suddenly moving on a tangent translucent screen. The responses of visual cortical cells to fast moving stimuli during steady fixation and those obtained during rapid eye movements (saccades) which moved their receptive field across a stationary stimulus, were studied. Areas V1 and V2 were explored. When tested with rapidly moving stimuli (500 deg/sec) during steady fixation, neurons in each area behaved in almost the same way. About one fourth of them were activated, the remainder showing either no response (little more than a half of them) or a reduction of the spontaneous firing rate. In both areas, some of the neurons activated during steady fixation did not respond or responded very weakly during eye motion at saccadic velocity (500 +/- 50 deg/sec). Neurons of this type, which we refer to as 'real motion' cells, could somehow contribute to the maintenance of visual stability during the execution of large eye movements.