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ABSTRACT: Reliable assessment of seismic performance of structural systems requires accurate and robust simulation techniques that can efficiently predict inelastic response in the large deformation range, up to structural collapse. This paper presents a real-time dynamic substructuring (RTDS) test program carried out on steel moment resisting frames (MRF) tested up to near collapse. A single-story, industrial building with steel MRFs at perimeter was examined applying the Loma Prieta earthquake record. Columns were pinned at their bases, while full stiffness and resistance was retained at beam-to column joints. The physical substructure included only one column that was installed in the inverted position i.e. clamped at the base and pinned at the top: in this way only one lateral degree of freedom was involved in physical tests. The other column, the beam, building masses, gravity loads and damping forces were included in the numerical substructure. Time integration was performed using a variant of a Rosenbrock-W scheme implemented into the Math Works's Simulink and XPC target computer environment. The tangent stiffness matrix of the structure was evaluated using different numerical strategies including data smoothing and filtering. Control techniques with constant or adaptive delay compensation for the feed-forward filter were implemented. The obtained results are compared and discussed to highlight the effect on structural response predictions. As a result, RTDS tests appear to be effective in the prediction of near collapse seismic response of steel frames, provided that robust numerical strategies are implemented.
American Control Conference (ACC), 2011; 08/2011
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ABSTRACT: In most of quantum-dot (QD) systems, the electrical behavior of a single QD is directly linked to the native oxide grown on their surface. Obtaining quantitative electrical measurements requires identifying this oxide well, which is not a trivial task. Due to the use of two conductive atomic force microscopy (C-AFM) probes of different behaviors, C-AFM experiments and local electrical measurements allow one to determine the barrier heights at the interface between InAs QD and the native oxide and then to deduce the oxide band gap. In the case of InAs/GaAs QDs, based on our work and on literature results, it may be assumed that the capping oxide is an InAs oxide enriched in indium.
IEEE Transactions on Electron Devices 07/2010; · 2.32 Impact Factor
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ABSTRACT: Although cognitive impairment after cerebellar damage has been widely reported, the mechanisms of cerebro-cerebellar interactions are still a matter of debate. The cerebellum is involved in sequence detection and production in both motor and sensory domains, and sequencing has been proposed as the basic mechanism of cerebellar functioning. Furthermore, it has been suggested that knowledge of sequencing mechanisms may help to define cerebellar predictive control processes. In spite of its recognized importance, cerebellar sequencing has seldom been investigated in cognitive domains. Cognitive sequencing functions are often analysed by means of action/script elaboration. Lesion and activation studies have localized this function in frontal cortex and basal ganglia circuits. The present study is the first to report deficits in script sequencing after cerebellar damage. We employed a card-sequencing test, developed ad hoc, to evaluate the influence of the content to be sequenced. Stimuli consisted of sets of sentences that described actions with a precise logical and temporal sequence (Verbal Factor), sets of cartoon-like drawings that reproduced behavioural sequences (Behavioural Factor) or abstract figures (Spatial Factor). The influence of the lesion characteristics was analysed by grouping patients according to lesion-type (focal or atrophic) and lesion-side (right or left). The results indicated that patients with cerebellar damage present a cognitive sequencing impairment independently of lesion type or localization. A correlation was also shown between lesion side and characteristics of the material to be sequenced. Namely, patients with left lesions perform defectively only on script sequences based on pictorial material and patients with right lesions only on script sequences requiring verbal elaboration. The present data support the hypothesis that sequence processing is the cerebellar mode of operation also in the cognitive domain. In addition, the presence of right/left and pictorial/verbal differences is in agreement with the idea that cerebro-cerebellar interactions are organized in segregated cortico-cerebellar loops in which specificity is not related to the mode of functioning, but to the characteristics of the information processed.
Brain 06/2008; 131(Pt 5):1332-43. · 9.46 Impact Factor
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ABSTRACT: An AFM combined with a SEM has been used to study the topography and the local electronic transport through InAs QDs grown by metalorganic vapour phase epitaxy (MOVPE) on an n-type InP(0 0 1) substrate and covered by a 5 nm thick InP cap-layer. Images reveal that elliptic terrace-like structures have been formed around the QDs and that the height of the QDs has been decreased to that of the cap-layer. The electric current is very high on the dots, about ten times less on the terraces, and not detectable on the wetting layer. Mechanisms of electronic transport through the sample are discussed, based on current–voltage characteristics and energy band diagrams. The detection of the electron beam induced current (EBIC) with the conductive probe shows that the minority carrier diffusion length, the holes in our case, is about two times larger than that of the reference sample containing no QDs. Mechanisms of charge trapping inside the QDs and the surrounding terraces in forward bias conditions are also discussed. A temporary memory effect is evidenced.
Semiconductor Science and Technology 06/2007; 22(7):755. · 1.72 Impact Factor
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ABSTRACT: Conductive atomic force microscopy has been used to study the topography and the electric properties of InAs quantum dots (QDs) grown by metal organic vapor phase epitaxy on a n-type InP(001) substrate and covered with a 5 nm thick InP cap layer. Images reveal that the cap layer has not entirely covered the surface, but has formed rounded terracelike structures surrounding the QDs. A high current is detected on the QDs, about ten times less on the terraces, and not detectable on the wetting layer. Charges can be trapped inside the QDs and the surrounding terraces in forward bias conditions with a temporary memory effect and discharged in reverse bias.
Applied Physics Letters 09/2006; 89(11):112115-112115-3. · 3.84 Impact Factor
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ABSTRACT: Cerebellar involvement in spatial data management has been suggested on experimental and clinical grounds.
To attempt a specific analysis of visuospatial abilities in a group of subjects with focal or atrophic cerebellar damage.
Visuospatial performance was tested using the spatial subtests of the WAIS, the Benton line orientation test, and two tests of mental rotation of objects-the Minnesota paper form board test (MIN) and the differential aptitude test (DAT).
In the Benton line orientation test, a test of sensory analysis and elementary perception, no deficits were present in subjects with cerebellar damage. In MIN, which analyses the capacity to process bidimensional complex figures mentally, and in the DAT, which is based on mental folding and manipulation of tridimensional stimuli, subjects with cerebellar damage were impaired.
The results indicate that lesions of the cerebellar circuits affect visuospatial ability. The ability to rotate objects mentally is a possible functional substrate of the observed deficits. A comparison between visuospatial performance of subjects with focal right and left cerebellar lesions shows side differences in the characteristics of the visuospatial syndrome. Thus cerebellar influences on spatial cognition appear to act on multiple cognitive modules.
Journal of Neurology Neurosurgery & Psychiatry 03/2004; 75(2):235-40. · 4.76 Impact Factor
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ABSTRACT: This study investigated the organization of the callosal connections of the two subdivisions of the monkey dorsal premotor cortex (PMd), dorso-rostral (F7) and dorso-caudal (F2). In one animal, Fast blue and Diamidino yellow were injected in F7 and F2, respectively; in a second animal, the pattern of injections was reversed. F7 and F2 receive a major callosal input from their homotopic counterpart. The heterotopic connections of F7 originate mainly from F2, with smaller contingent from pre-supplementary motor area (pre-SMA, F6), area 8 (frontal eye fields), and prefrontal cortex (area 46), while those of F2 originate from F7, with smaller contributions from ventral premotor areas (F5, F4), SMA-proper (F3), and primary motor cortex (M1). Callosal cells projecting homotopically are mostly located in layers II-III, those projecting heterotopically occupy layers II-III and V-VI. A spectral analysis was used to characterize the spatial fluctuations of the distribution of callosal neurons, in both F7 and F2, as well as in adjacent cortical areas. The results revealed two main periodic components. The first, in the domain of the low spatial frequencies, corresponds to periodicities of cell density with peak-to-peak distances of approximately 10 mm, and suggests an arrangement of callosal cells in the form of 5-mm wide bands. The second corresponds to periodicities of approximately 2 mm, and probably reflects a 1-mm columnar-like arrangement. Coherency and phase analyses showed that, although similar in their spatial arrangements, callosal cells projecting to dorsal premotor areas are segregated in the tangential cortical domain.
European Journal of Neuroscience 09/2003; 18(4):775-88. · 3.63 Impact Factor
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ABSTRACT: By combining an observational spatial learning paradigm with a cerebellar lesion that blocks the acquisition of new spatial strategies, it is possible to separate a complex spatial behavior into its fundamental units to study which relationships among units have to be maintained so that the entire behavior might be acquired. Normal rats were first allowed to observe demonstrator rats performing single explorative behaviors (circling, extended searching, direct finding), then were hemicerebellectomized and, finally, tested in the Morris water maze. In spite of the cerebellar lesion, the observer rats displayed exploration abilities that closely matched the previously observed behaviors. These results indicate that the single facets that form the strategy repertoire can be independently acquired.
Behavioral Neuroscience 03/2002; 116(1):116-25. · 2.62 Impact Factor
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ABSTRACT: The comprehension of the cerebellar physiology is rapidly changing in particular because of the demonstration of the cerebellar importance on cognition. In the present paper, recent data on cerebro cerebellar interactions is reviewed, particularly focusing on cerebellar influences over the neurophysiology of primary motor and primary sensory cortices. The cerebellar role in implicit learning and in sensory data processing is analysed and discussed. It is proposed that the cerebellum could control cortical plastic changes by modulating cortical excitability in a discrete topographic manner and that this mechanism could induce the coupling between significant sensory inputs and definite motor outputs considered as the neurobiological substrate for implicit learning.
Neuroscience 02/2002; 111(4):863-70. · 3.38 Impact Factor
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ABSTRACT: The anatomical and physiological substrata of eye-hand coordination during reaching were studied through combined anatomical and physiological techniques. The association connections of parietal areas V6A and PEc, and those of dorso-rostral (F7) and dorso-caudal (F2) premotor cortex were studied in monkeys, after physiological characterization of the parietal regions where retrograde tracers were injected. The results show that parieto-occipital area V6A is reciprocally connected with F7, and receives a smaller projection from F2. Local parietal projections to V6A arise from areas MIP and, to a lesser extent, 7m, PEa and PEC: On the contrary, parietal area PEc is strongly and reciprocally connected with the part of F2 located close to the pre-central dimple (pre-CD). Local parietal projections to PEc come from a distributed network, including PEa, MIP, PEci and, to a lesser extent, 7m, V6A, 7a and MST. Premotor area F7 receives parietal projections mainly from 7m and V6A, and local frontal projections mainly from F2. On the contrary, premotor area F2 in the pre-CD zone receives parietal inputs from PEc and, to a lesser extent, PEci, while in the peri-arcuate zone F2 receives parietal projections from PEa and MIP. Local frontal projections to F2 pre-CD mostly stem from F4, and, to a lesser extent, from F7 and F3, and CMAd; those addressed to peri-arcuate zone of F2 arise mainly from F5 and, to a lesser extent, from F7, F4, dorsal (CMAd) and ventral (CMAv) cingulate motor areas, pre-supplementary (F6) and supplementary (F3) motor areas. The distribution of association cells in both frontal and parietal cortex was characterized through a spectral analysis that revealed an arrangement of these cells in the form of bands, composed of cell clusters, or 'columns'. The reciprocal connections linking parietal and frontal cortex might explain the presence of visually related and eye-position signals in premotor cortex, as well as the influence of information about arm position and movement direction in V6A and PEC: The association connections identified in this study might carry sensory as well motor information that presumably provides a basis for a re-entrant signaling. This might be necessary to match retinal-, eye- and hand-related information underlying eye-hand coordination during reaching.
Cerebral Cortex 07/2001; 11(6):513-27. · 6.54 Impact Factor
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ABSTRACT: The relationships between the distribution of visuomanual signals in parietal cortex and that of parieto-frontal projections are the subject of the present study. Single cell recording was performed in areas PEc and V6A, where different anatomical tracers were also injected. The monkeys performed a variety of behavioral tasks, aimed at studying the visual and motor properties of parietal cells, as well as the potential combination of retinal-, eye- and hand-related signals on cell activity. The activity of most cells was related to the direction of movement and the active position of the hand. Many of these reach-related cells were influenced by eye position information. Fewer cells displayed relationships to saccadic eye movements. The activity of most neurons related to a combination of both hand and eye signals. Many cells were also modulated during preparation for hand movement. Light-dark differences of activity were common and interpreted as related to the sight and monitoring of hand motion and/or position in the visual field. Most cells studied were very sensitive to moving visual stimuli and also responded to optic flow stimulation. Visual receptive fields were generally large and extended to the periphery of the visual field. For most neurons, the orientation of the preferred directions computed across different epochs and tasks conditions clustered within a limited sector of space, the field of global tuning. This can be regarded as an ideal frame to combine spatially congruent eye- and hand-related information for different forms of visuomanual behavior. All these properties were common to both PEc and V6A. Retinal, eye- and hand-related activity types, as well as parieto-frontal association cells, were distributed in a periodic fashion across the tangential domain of areas PEc and V6A. These functional and anatomical distributions were characterized and compared through a spectral and coherency analysis, which revealed the existence of a selective 'match' between activity types and parieto-frontal connections. This match depended on where each individual efferent projection was addressed. The results of the present and of the companion study can be relevant for a re-interpretation of optic ataxia as the consequence of the breakdown of the combination of retinal-, eye- and hand-related directional signals within the global tuning fields of parietal neurons.
Cerebral Cortex 07/2001; 11(6):528-44. · 6.54 Impact Factor
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ABSTRACT: Although cerebellar lesions do not cause evident sensory deficits, it has been suggested recently that the cerebellum might play a role in sensory acquisition and discrimination. To determine whether the cerebellum influences the early phases of cortical somatosensory processing, we recorded cortical somatosensory evoked potentials after median nerve stimulation in five patients with unilateral cerebellar damage. We also performed a dipolar source analysis of traces by means of brain electrical source analysis. In all patients, the amplitude of the frontal N24 and parietal P24 components, as well as the strength of the corresponding dipolar sources, were significantly smaller after stimulation of the symptomatic side. These neurophysiological findings indicate that the primary somatosensory cortical processing is altered after contralateral cerebellar damage. They represent the first indication of a possible substrate for the reduction in cerebral blood flow observed in the parietal cortex after cerebellar lesion. Furthermore, the present data allow characterization of the functional influence of the cerebellar input to the primary somatosensory cortex as specifically acting over the inhibitory components of somatosensory processing.
Brain 05/2001; 124(Pt 4):757-68. · 9.46 Impact Factor
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ABSTRACT: Recent clinical and functional neuroimaging evidence points towards a cerebellar role in verbal production. At present it is not clear how the cerebellum participates in language production. The aim was to investigate the influence of cerebellar lesions on verbal fluency abilities with specific focus on the verbal searching strategies employed by patients with cerebellar damage.
Twenty five patients with focal or degenerative cerebellar disease and 14 control subjects were tested in a timed verbal fluency task requiring word production under forced (phonemic or semantic) conditions. To analyse the verbal searching strategy employed, semantic and phonemic cluster analyses were also performed.
Performances of cerebellar patients were comparable with those of controls in the semantic task; conversely their performances were significantly impaired when tested in the letter task. Cluster analysis results showed that the verbal fluency impairment is linked to specific damage of phonemically related retrieval strategies.
Cerebellar damage impairs verbal fluency by specifically affecting phonemic rule performances while sparing semantic rule ones. These findings underline the importance of the cerebellar computing properties in strategy development in the linguistic domain.
Journal of Neurology Neurosurgery & Psychiatry 08/2000; 69(1):102-6. · 4.76 Impact Factor
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ABSTRACT: Experimental evidence demonstrates that cerebellar networks are involved in spatial learning, controlling the acquisition of exploration strategies without blocking motor execution of the task. Action learning by observation has been considered somehow related to motor physiology, because it provides a way of learning performances that is almost as effective as the actual execution of actions. Neuroimaging studies demonstrate that observation of movements performed by others, imagination of actions, and actual execution of motor performances share common neural substrates and that the cerebellum is among these shared areas. The present paper analyzes the effects of observation in learning a spatial task, focusing on the cerebellar role in learning a spatial ability through observation. We allowed normal rats to observe 200 Morris water maze trials performed by companion rats. After this observation training, "observer" rats underwent a hemicerebellectomy and then were tested in the Morris water maze. In spite of the cerebellar lesion, they displayed no spatial defects, exhibiting exploration abilities comparable to controls. When the cerebellar lesion preceded observation training, a complete lack of spatial observational learning was observed. Thus, as demonstrated already for the acquisition of spatial procedures through actual execution, cerebellar circuits appear to play a key role in the acquisition of spatial procedures also through observation. In conclusion, the present results provide strong support for a common neural basis in the observation of actions that are to be reproduced as well as in the actual production of the same actions.
Proceedings of the National Academy of Sciences 03/2000; 97(5):2320-5. · 9.68 Impact Factor
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R Caminiti,
A Genovesio,
B Marconi,
A B Mayer,
P Onorati,
S Ferraina,
T Mitsuda,
S Giannetti,
S Squatrito,
M G Maioli, M Molinari
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ABSTRACT: The ipsilateral association connections of the cortex of the dorsal part of the rostral bank of the parieto-occipital sulcus and of the adjoining posterior part of the superior parietal lobule were studied by using different retrograde fluorescent tracers. Fluoro-Ruby, Fast blue and Diamidino yellow were injected into visual area V6A, and dorso-caudal (PMdc, F2) and dorso-rostral (PMdr, F7) premotor cortex, respectively. The parietal area of injection had been previously characterized physiologically in behaving monkeys, through a variety of oculomotor and visuomanual tasks. Area V6A is mainly linked by reciprocal projections to parietal areas 7m, MIP (medial intraparietal) and PEa, and, to a lesser extent, to frontal areas PMdr (rostral dorsal premotor cortex, F7) and PMdc (F2). All these areas project to that part of the dorsocaudal premotor cortex that has a direct access to primary motor cortex. V6A is also connected to area F5 and, to a lesser extent, to 7a, ventral (VIP) and lateral (LIP) intraparietal areas. This pattern of association connections may explain the presence of visually-related and eye-position signals in premotor cortex, as well as the influence of information concerning arm position and movement direction on V6A neural activity. Area V6A emerges as a potential 'early' node of the distributed network underlying visually-guided reaching. In this network, reciprocal association connections probably impose, through re-entrant signalling, a recursive property to the operations leading to the composition of eye and hand motor commands.
European Journal of Neuroscience 10/1999; 11(9):3339-45. · 3.63 Impact Factor
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ABSTRACT: Recently, we demonstrated the prevalent role of cerebellar networks in the acquisition of the procedural components of spatial information by testing hemicerebellectomized (HCbed) rats in a classical spatial task, the Morris water maze (MWM). As procedures used in the water maze are a mixture of different components (that is, general procedures, exploration procedures, direct reaching procedures), for optimally solving a spatial task all procedural components must be opportunely managed. Thus, severely impaired procedural learning of cerebellar origin can be better comprehended by fractionating the procedural facets. To this aim, a two-step water-maze paradigm was employed. Normal rats were first trained to search for a hidden platform moved to a different position in each trial, utilizing a water maze setting in which visual cues were abolished by heavy black curtains surrounding the tank. In this paradigm, normal animals solved the task by using general and exploration procedures, but they could not use direct reaching skills. A subgroup of these pretrained animals was then HCbed and, after recovery from cerebellar lesion, was tested in a water maze with normal environmental cues available, a paradigm in which normal animals develop abilities for reaching the target with very direct trajectories. Pretrained HCbed animals, however, did not display the typical spatial deficits of naive HCbed rats, persisted in exhibiting the scanning strategy learned during pretraining, and never displayed direct reaching skills. In conclusion, cerebellar networks appear to be involved in the acquisition of all procedural facets necessary for shifting behavior within the maze until direct reaching of the platform. The lack of flexibility in changing exploration strategies displayed by pretrained HCbed rats is interpreted by taking into account the well-known cerebellar frontal interplay sculpting a specific cerebellar role in the acquisition of spatial procedural steps.
Experimental Brain Research 08/1999; 127(1):1-11. · 2.39 Impact Factor
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Journal of Neurology 05/1999; 246(4):312-3. · 3.47 Impact Factor
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ABSTRACT: We describe an 18-year-old patient who underwent surgical removal of the right cerebellar hemisphere for the presence of a neoplastic lesion. After surgery, the patient's neuropsychological examination was normal except for a transient selective verbal short-term memory (STM) impairment characterized by reduced verbal digit span and rapid forgetting of verbal material. An extensive examination of the patient's deficit was performed in order to identify which of the two components of STM (phonological short-term store and/or rehearsal system) was impaired. The functional locus of the deficit was identified at the level of the phonological output buffer, a component of the rehearsal system, as suggested by the pattern of results obtained, namely: the improvement of the digit span seen with pointing compared with the verbal response; the advantage of auditory over visual presentation of digits; and the lack of a phonological-similarity effect with visual presentation of letters. On the other hand, the functioning of the phonological store was demonstrated by the normal amplitude of the recency effect in free recall of words and by the phonological-similarity effect with auditory presentation of letters. Our finding is consistent with previous functional (PET) studies showing the involvement of the right cerebellum during tasks requiring silent recirculation of verbal information. We conclude that the cerebellum takes part in the planning of speech production at a level that does not require an overt articulation.
Brain 12/1998; 121 ( Pt 11):2175-87. · 9.46 Impact Factor
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ABSTRACT: The aim of the present study was to investigate the influence of focal cerebellar lesions on procedural learning. Eight patients with cerebellar lesions and six control subjects were tested in a serial reaction-time task. A four-choice reaction-time task was employed in which the stimuli followed (or not) a sequence repeated 10 times, with the subjects aware (or not) of the item sequence. Learning was manifested by the reduction in response latency over the sequential blocks. Acquisition of declarative knowledge of the sequence was also tested. Reaction times displayed by patients with cerebellar lesions, even though they tended to be longer than those of control subjects in all testing conditions, significantly differed from control subjects only when the stimuli were presented in sequence. The reaction times in sequential trials were still statistically significant when simple motor response times were taken into account. Cerebellar patients were also significantly impaired in detecting and repeating the sequence. On the other hand, when the sequence was learned before testing, motor performances were significantly improved in all subjects. These data indicate that cerebellar lesions induce specific impairment in the procedural learning of a motor sequence and suggest a role of the cerebellar circuitry in detecting and recognizing event sequences.
Brain 11/1997; 120 ( Pt 10):1753-62. · 9.46 Impact Factor
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ABSTRACT: Recently, we demonstrated the involvement of cerebellar circuits in the procedural components of spatial information processing by testing hemicerebellectomized (HCbed) rats in classical spatial paradigms, such as the Morris Water Maze and the water T-maze. Since procedural components are strongly present in these tests, an impairment also in processing more abstract spatial information, linked to 'where an object is' rather than to 'how to find it', could be hidden by the severe procedural deficits. On this basis, we investigated the influence of cerebellar lesions on spatial abilities strictly reducing procedural variables by employing an active avoidance task, first without and then with a request for right/left discrimination. In the two-way active avoidance task without spatial requests, controls and cerebellar operated rats developed active avoidance responses which were not statistically different, demonstrating that this kind of associative learning is not significantly affected by hemicerebellectomy (HCb). A second experimental group of cerebellar lesioned rats was tested in a modified version of this basic paradigm in which a right/left discrimination request was added. This group displayed severe deficits, which even in the last testing sessions prevented them from performing comparably to the control animals. Reversal of the rewarded choice, even if it affected the performances of both controls and operated rats in the first inversion trials, elicited the lowest number of correct responses in HCbed rats throughout the entire spatial reversal learning, suggesting a severe deficit in the ability to change an initially learned behaviour. These results demonstrate that, beside having a marked impairment in facing procedural components of spatial processing, cerebellar lesioned rats are severely defective also in right/left discrimination tasks, suggesting a role of cerebellar networks also in the discriminative spatial information processing.
European Journal of Neuroscience 10/1997; 9(9):1986-92. · 3.63 Impact Factor
