Discrepancies between cortical and behavioural long-term readouts of hyperalgesia in awake freely moving rats.

BACKGROUND: It is still unclear to what extent the most common animal models of pain and analgesia, based on indirect measures such as nocifensive behaviours, provide valid measures of pain perception. METHODS: To address this issue, we developed a novel animal model comprising a more direct readout via chronically (>1 month) implanted multichannel electrodes (MCE) in rat primary somatosensory cortex (S1; known to be involved in pain perception in humans) and compared this readout to commonly used behavioural pain-related measures during development of hyperalgesia. A translational method to induce hyperalgesia, UVB irradiation of the skin, was used. Localized CO2 laser stimulation was made of twenty skin sites (20 stimulations/site/observation day) on the plantar hind paw, before and during the time period when enhanced pain perception is reported in humans after UVB irradiation. RESULTS: We demonstrate a 2-10 fold significant enhancement of cortical activity evoked from both irradiated and adjacent skin and a time course that corresponds to previously reported enhancement of pain magnitude during development of primary and secondary hyperalgesia in humans. In contrast, withdrawal reflexes were only significantly potentiated from the irradiated skin area and this potentiation was significantly delayed as compared to activity in S1. CONCLUSIONS: The present findings provide direct evidence that chronic recordings in S1 in awake animals can offer a powerful, and much sought for, translational model of the perception of pain magnitude during hyperalgesia. WHAT DOES THIS STUDY ADD?: In a novel animal model, chronic recordings of nociceptive activity in primary somatosensory cortex (S1) in awake freely moving rats are compared to behavioural readouts during UVB-induced hyperalgesia. Evoked activity in rat S1 replicates altered pain perception in humans during development of hyperalgesia, but withdrawal reflexes do not.

Spike-feature based estimation of electrode position in extracellular neural recordings.

Detecting and sorting spikes in extracellular neural recordings are common procedures in assessing the activity of individual neurons. In chronic recordings, passive electrode movements introduce changes in the shape of detected spike waveforms, and may thus lead to problems with identification and tracking of spikes recorded at separate instances in time, which is an important step in long-term monitoring of individual neurons. Information about electrode movements after implantation is crucial to the evaluation of mechanical stability of different electrode designs. In this paper, we present a preliminary study of the relationship between electrode movements and the resulting movements of spike-features in feature space. We show that there is a characteristic relationship between the two movements and that this relationship can be modeled as a linear transformation between two coordinate systems. Finally, we show how the relationship can be used for estimating electrode positions based on measured spike waveforms without any prior knowledge about the type of neuron by introducing a learning procedure during electrode insertion.

Statistical modelling of spike libraries for simulation of extracellular recordings in the cerebellum.

Brain machine interfaces with chronically implanted microelectrode arrays for signal acquisition require algorithms for successful detection and classification of neural spikes. During the design of such algorithms, signals with a priori known characteristics need to be present. A common way to establish such signals is to model the recording environment, simulate the recordings and store ground truth about spiking activity for later comparison. In this paper, we present a statistical method to expand the spike libraries that are used in a previously presented simulation tool for the purpose described above. The method has been implemented and shown to successfully provide quick access to a large assembly of synthetic extracellular spikes with realistic characteristics. Simulations of extracellular recordings using synthesized spikes have shown to possess characteristics similar to those of in-vivo recordings in the cat cerebellum.

Flexible multi electrode brain-machine interface for recording in the cerebellum.

A new type of chip based microelectrode for acute electrophysiological recordings in the CNS has been developed. It's designed to be adaptable to a multitude of specific neuronal environments, in this study the cerebellar cortex of rat and cat. Photolithographically patternened SU-8 is used to yield flexible and biocompatible penetrating shanks with gold leads. Electrodes with an impedance of about 300 kOmega at 1kHz have excellent signal to noise ratio in acute recordings in cat cerebellum.

Spike library based simulator for extracellular single unit neuronal signals.

A well defined set of design criteria is of great importance in the process of designing brain machine interfaces (BMI) based on extracellular recordings with chronically implanted micro-electrode arrays in the central nervous system (CNS). In order to compare algorithms and evaluate their performance under various circumstances, ground truth about their input needs to be present. Obtaining ground truth from real data would require optimal algorithms to be used, given that those exist. This is not possible since it relies on the very algorithms that are to be evaluated. Using realistic models of the recording situation facilitates the simulation of extracellular recordings. The simulation gives access to a priori known signal characteristics such as spike times and identities. In this paper, we describe a simulator based on a library of spikes obtained from recordings in the cat cerebellum and observed statistics of neuronal behavior during spontaneous activity. The simulator has proved to be useful in the task of generating extracellular recordings with realistic background noise and known ground truth to use in the evaluation of algorithms for spike detection and sorting.

Implementation of a telemetry system for neurophysiological signals.

With an ever increasing need for assessment of neurophysiological activity in connection with injury and basic research, the demand for an efficient and reliable data acquisition system rises. Brain-machine interfaces is one class of such systems that targets the central nervous system. A necessary step in the development of a brain-machine interface is to design and implement a reliable and efficient measurement system for neurophysiological signals. The use of telemetric devices increases the flexibility of the devices in terms of subject mobility and unobtrusiveness of the equipment. In this paper, we present a complete system architecture for a wearable telemetry system for the acquisition of neurophysiological data. The system has been miniaturized and implemented using surface-mount technology. System performance has been successfully verified and bottlenecks in the architecture have been identified.

Functional organization of climbing fibre projection to the cerebellar anterior lobe of the rat.

1. The input characteristics and distribution of climbing fibre field potentials evoked by electrical stimulation of various parts of the skin were investigated in the cerebellum of barbiturate anaesthetized rats. 2. Climbing fibre responses were recorded in sagittally oriented microelectrode tracks across the mediolateral width of the anterior lobe. Climbing fibres with similar response latencies and convergence patterns terminated in sagittal bands with widths of 0.5-1.5 mm. The principal organization of the anterior lobe with respect to input characteristics and locations of sagittal zones was similar to that in the cat and ferret. Hence, the sagittal bands in the rat were tentatively named the a, b, c1, c2 and d1 zones. 3. In contrast to the cat and ferret, the a zone of the rat was characterized by short latency ipsilateral climbing fibre input. Furthermore, it was divisible into a medial 'a1' zone with convergent, proximal input and a lateral 'ax' zone with somatotopically organized input. A forelimb area with similar location and input characteristics as the X zone of the cat was found, but it formed an integral part of the ax zone. A somatotopic organization of ipsilateral, short latency climbing fibre input was also found in the c1 zone. 4. Rostrally in the anterior lobe, climbing fibres activated at short latencies from the ipsilateral side of the body terminated in a somatotopically organized transverse band which extended from the midline to the lateral end of the anterior lobe. 5. The absence of the C3 and Y zones may be interpreted as a reflection of differences in the organization of the motor systems in the rat as compared with the cat. Skilled movements, which in the cat are controlled by the C1, C3 and Y zones via the anterior interposed nucleus, may in the rat be partly controlled by the ax zone via the rostrolateral part of the fastigial nucleus.

Precise matching of olivo-cortical divergence and cortico-nuclear convergence between somatotopically corresponding areas in the medial C1 and medial C3 zones of the paravermal cerebellum.

The paravermal cerebellar cortex contains three spatially separate zones (the C1, C3 and Y zones) which form a functionally coupled system involved in the control of voluntary limb movements. A series of 'modules' has been postulated, each defined by a set of olivary neurons with similar receptive fields, the cortical microzones innervated by these neurons and the group of deep cerebellar nuclear neurons upon which the microzones converge. A key feature of this modular organization is a correspondence between cortical input and output, irrespective of the zonal identity of the microzone. This was tested directly using a combined electrophysiological and bi-directional tracer technique in barbiturate-anaesthetized cats. During an initial operation, small injections of a mix of retrograde and anterograde tracer material (red beads combined with Fluoro-Ruby or green beads combined with biotinylated dextran amine or Fluoro-Emerald) were made into areas of the medial C1 and medial C3 zones in cerebellar lobule V characterized by olivo-cerebellar input from the ventral forelimb. The inferior olive and the deep cerebellar nuclei were then scrutinized for retrogradely labelled cells and anterogradely labelled axon terminals, respectively. For individual experiments, the degree of C1-C3 zone terminal field overlap in the nucleus interpositus anterior was plotted as a function of either the regional overlap of single-labelled cells or the proportion of double-labelled cells in the dorsal accessory olive. The results were highly positively correlated, indicating that cortico-nuclear convergence between parts of the two zones is in close proportion to the corresponding olivo-cerebellar divergence, entirely consistent with the modular hypothesis.

Sensorimotor transformation in cat nociceptive withdrawal reflex system.

The withdrawal reflex system of higher vertebrates has been extensively used as a model for spinal sensorimotor integration, nociceptive processing and plasticity. In the rat, the nociceptive withdrawal reflex system appears to have a modular organization. Each reflex module controls a single muscle or a few synergistic muscles, and its cutaneous receptive field corresponds to the skin area withdrawn upon contraction of the effector muscle(s) when the limb is in the standing position. This organization principle is at odds with the 'flexion reflex' concept postulated from cat studies. To assess the generality of the modular organization principle we have therefore re-examined the cutaneous input to the withdrawal reflex system of the cat. The cutaneous receptive fields of hindlimb and forelimb muscles were mapped using calibrated noxious pinch stimulation and electromyographic recording technique in barbiturate anaesthetized animals. The investigated muscles had specific cutaneous receptive fields that appeared to correspond to the area of the skin withdrawn upon contraction of the muscle when the limb is in the standing position. The spatial organization of receptive fields in the cat was similar to that in the rat. However, differences in gain properties of reflexes to some anatomically equivalent muscles in the two species were observed, possibly reflecting adaptations to the biomechanics characteristic of the digitigrade and plantigrade stance in cats and rats, respectively. Implications of the findings for the generality of the modular organization of the withdrawal reflex system and for its adaptive properties are discussed.

Cutaneous receptive fields and topography of mossy fibres and climbing fibres projecting to cat cerebellar C3 zone.

1. The topographical organization of mossy fibre input to the forelimb area of the paravermal C3 zone in cerebellar lobules IV and V was investigated in barbiturate-anaesthetized cats and compared with the previously described microzonal organization of climbing fibre input to the same part of the cortex. Recordings were made in the Purkinje cell and granule cell layers from single climbing fibre and mossy fibre units, respectively, and the organization of cutaneous receptive fields was assessed for both types of afferents. 2. Based on spatial characteristics, receptive fields of single mossy fibres could be systematized into ten classes and a total of thirty-two subclasses, mainly in accordance with a scheme previously used for classification of climbing fibres. Different mossy fibres displayed a substantial range of sensitivity to natural peripheral stimulation, responded preferentially to phasic or tonic stimuli and were activated by brushing of hairs or light tapping of the skin. 3. Overall, mossy fibres to any given microzone had receptive fields resembling the climbing fibre receptive field defining that microzone. However, compared with the climbing fibre input, the mossy fibre input had a more intricate topographical organization. Mossy fibres with very similar receptive fields projected to circumscribed cortical regions, with a specific termination not only in the mediolateral, but also in some cases in the rostrocaudal and dorsoventral, dimensions of the zone. On the other hand, mossy fibre units with non-identical, albeit usually similar, receptive fields were frequently found in the same microelectrode track.

Gating of cutaneous input to cerebellar climbing fibres during a reaching task in the cat.

1. Task-dependent modulation of cutaneous input to climbing fibres projecting to the C1, C2 and C3 zones in the cerebellar paravermal lobule V was investigated in awake cats during performance of a reaching task. 2. Climbing fibre responses resulting from low intensity (non-noxious) electrical stimulation of the ipsilateral superficial radial nerve were recorded as extracellular field potentials in the cerebellar cortex using chronically implanted microwires. 3. Response size, measured as the time-voltage integral of the evoked field potential, was assessed during three phases of the reaching movement, reaction, reach and grasp, and compared with the response size at rest. 4. At C1 and C3 zone recording sites response size was usually reduced during the task (7/10 sites). The reduction was most pronounced in the grasp phase, occasionally accompanied by a smaller reduction in the reach and reaction phases. In one case an enhancement was found in the reach phase. 5. Response size was also modulated during the task at four of six C2 zone recording sites. However, the results were mixed. In three cases the modulation resembled the pattern at C1/C3 sites with the responses being reduced in the grasp phase accompanied on occasion by a lesser reduction in the reach phase. In the remaining case there was an enhancement during grasp. In this case and one other there was also an enhancement during the reaction phase. 6. The findings indicate significant gating of cutaneous input to climbing fibres projecting to the C1, C2 and C3 zones during reaching movements, while the variability between recording sites suggests functional differences, both between and within zones.

The control of forelimb movements by intermediate cerebellum.

In a series of studies, the functional organization of cerebellar regions contributing to the control of forelimb movements via the rubro- and corticospinal tracts has been characterized in the cat. The system consists of the cerebellar cortical C1, C3 and Y zones and their efferent intracerebellar nucleus, the interpositus anterior. Based on analyses of cutaneous and muscle afferent climbing fibre input, of corticonuclear connections and of limb movements controlled, a modular organization of this cerebellar control system is proposed. Each module consists of a number of cortical microzones, defined by their homogeneous climbing fibre input, and a group of neurones in nucleus interpositus anterior on which these microzones converge. The input to climbing fibres is multi-modal and originates from cutaneous A beta (tactile), A delta and C (nociceptive) fibres and from muscle afferents. The cutaneous receptive fields have spatial characteristics suggestive of a relation to elemental movements. For most climbing fibres, the spatial relationship between cutaneous and muscle afferent input is such that the muscle afferent input originates from muscles that, if activated, would tend to move the cutaneous receptive field of the climbing fibre towards a stimulus applied to the skin. By contrast, the limb movement controlled by the module often has the opposite direction, and would thus tend to move the cutaneous receptive field away from a stimulus applied to the skin. Functional implications of this organization for the involvement of these regions in acute and adaptive motor control of limb movements are discussed.

Sagittal zonal organization of climbing fibre input to the cerebellar anterior lobe of the ferret.

The organization of climbing fibre input to the cerebellar anterior lobe of the ferret was investigated in barbiturate-anaesthetized animals. Climbing fibre field potentials evoked on electrical stimulation of forelimb and hindlimb nerves were recorded at the cerebellar surface. Based on characteristic latencies of climbing fibre responses and their relative localization along the longitudinal axis of the folia, nine sagittally oriented zones could be distinguished and were tentatively named, from medial to lateral, A, X, B, C1, Cx, C2, C3, D1 and D2. Within the C1, C2 and C3 zones, climbing fibre input from the ipsilateral forelimb was found caudally and from the hindlimb rostrally, while the corresponding topographical representation in the B and D2 zones was medial to lateral. The X, Cx and D1 zones did not receive input from the hindlimb, while input from the forelimb to the A zone was weak. Overall, the sagittal zonal organization of climbing fibre input appears to conform with the compartmentalization of the ferret cerebellum based on the myeloarchitecture of corticonuclear fibres, although the X and Cx zones have not been previously identified. In terms of both general electrophysiological characteristics of input to different zones and intrazonal topographical representation, the organization of climbing fibre input to the ferret cerebellum seems to strongly resemble that in the cat. The findings thus provide evidence of cross-species generality of cerebellar sagittal organization.

Micro-organization of olivocerebellar and corticonuclear connections of the paravermal cerebellum in the cat.

The olivocerebellar and corticonuclear connections of the forelimb area of the paravermal medial C3 zone were studied in the cat using a combined electrophysiological and fluorescent tracer technique. During an initial operation under barbiturate anaesthesia, lobules IV/V of the cerebellar anterior lobe were exposed and small injections of dextran amines tagged with rhodamine or fluorescein were made into areas selected from four different electrophysiologically defined parts of the zone. The inferior olive and the deep cerebellar nuclei were then scrutinized for retrogradely labelled cells and anterogradely labelled axon terminals respectively. The findings demonstrate a detailed topographical organization within the olivocerebellar projection to the medial C3 zone and provide some evidence for a topographical organization of its projection to nucleus interpositus anterior. Both projections are described at a level of resolution not previously attained in neuroanatomical studies and the results strongly support the notion of a micro-compartmentalization of cerebellar olivo-corticonuclear circuits.

Relation between cutaneous receptive fields and muscle afferent input to climbing fibres projecting to the cerebellar C3 zone in the cat.

Inferior olivary cells projecting as climbing fibres to the forelimb area of the cerebellar C3 zone were investigated with respect to their cutaneous and muscle afferent input in barbiturate-anaesthetized cats. Climbing fibre responses were recorded from single cerebellar cortical Purkinje cells on natural stimulation of the skin and on electrical stimulation of nerves to m. biceps brachii, m. triceps brachii and to nine muscles acting as dorsal or palmar flexors of the paw (and, in some cases, the digits). The analysis was focused on the functional organization of convergence between cutaneous and muscle afferents onto single olivary neurons. Cutaneous receptive fields on the dorsal side of the paw and on the digits were generally associated with moderate to strong input from dorsal flexors, but little or no input from palmar flexors or proximal muscles. Receptive fields on the ventral side of the paw and forearm were associated with relatively strong input from biceps and palmar flexors. Climbing fibres with cutaneous receptive fields extending on the ulnar side of the paw and forearm usually received strong input from the triceps and moderate to strong input from dorsal flexors, whereas input from the palmar flexors was weak or lacking. In conclusion, the results indicate that the cutaneous receptive fields in many cases are associated with input from muscles the action of which would tend to move the receptive field towards a stimulus applied to the skin.

Functional relation between corticonuclear input and movements evoked on microstimulation in cerebellar nucleus interpositus anterior in the cat.

The functional relation between receptive fields of climbing fibres projecting to the C1, C3 and Y zones and forelimb movements controlled by nucleus interpositus anterior via the rubrospinal tract were studied in cats decerebrated at the pre-collicular level. Microelectrode tracks were made through the caudal half of nucleus interpositus anterior. This part of the nucleus receives its cerebellar cortical projection from the forelimb areas of these three sagittal zones. The C3 zone has been demonstrated to consist of smaller functional units called microzones. Natural stimulation of the forelimb skin evoked positive field potentials in the nucleus. These potentials have previously been shown to be generated by climbing fibre-activated Purkinje cells and were mapped at each nuclear site, to establish the climbing fibre receptive fields of the afferent microzones. The forelimb movement evoked by microstimulation at the same site was then studied. The movement usually involved more than one limb segment. Shoulder retraction and elbow flexion were frequently evoked, whereas elbow extension was rare and shoulder protraction never observed. In total, movements at the shoulder and/or elbow occurred for 96% of the interpositus sites. At the wrist, flexion and extension movements caused by muscles with radial, central or ulnar insertions on the paw were all relatively common. Pure supination and pronation movements were also observed. Movements of the digits consisted mainly of dorsal flexion of central or ulnar digits. A comparison of climbing fibre receptive fields and associated movements for a total of 110 nuclear sites indicated a general specificity of the input-output relationship of this cerebellar control system. Several findings suggested that the movement evoked from a particular site would act to withdraw the area of the skin corresponding to the climbing fibre receptive field of the afferent microzones. For example, sites with receptive fields on the dorsum of the paw were frequently associated with palmar flexion at the wrist, whereas sites with receptive fields on the ventral side of the paw and forearm were associated with dorsiflexion at the wrist. Correspondingly, receptive fields on the lateral side of the forearm and paw were often associated with flexion at the elbow, whereas sites with receptive fields on the radial side of the forearm were associated with elbow extension. The proximal movements that were frequently observed also for distal receptive fields may serve to produce a general shortening of the limb to enhance efficiency of the withdrawal. It has previously been suggested that the cerebellar control of forelimb movements via the rubrospinal tract has a modular organisation. Each module would consist of a cell group in the nucleus interpositus anterior and its afferent microzones in the C1, C3 and Y zones, characterised by a homogenous set of climbing fibre receptive fields. The results of the present study support this organisational principle, and suggest that the efferent action of a module is to withdraw the receptive field from an external stimulus. Possible functional interpretations of the action of this system during explorative and reaching movements are discussed.

Topographical organization of the cerebellar cortical projection to nucleus interpositus anterior in the cat.

1. A new methodological approach for detailed study of the organization of the cerebellar corticonuclear projection was evaluated in barbiturate-anaesthetized cats. Extracellular field potentials were simultaneously recorded in nucleus interpositus anterior and in the forelimb area of the C3 zone, at the cerebellar surface. On electrical and natural stimulation of the forelimb skin, the evoked positive field potentials in the nucleus and the climbing fibre field potentials in the cerebellar cortex had similar characteristics, indicating that the nuclear potentials were related to climbing fibre activity. 2. Application of a local anaesthetic to the cerebellar surface reversibly diminished the positive field potentials in the nucleus, demonstrating that the potentials were dependent on cerebellar cortical activity. It was thus concluded that the positive field potentials were mainly generated by climbing fibre-activated Purkinje cells and reflected synaptic inhibitory potentials in nuclear neurones. Accordingly, the positive field potentials in the nucleus could be used to reveal the termination area of Purkinje cells activated by a specific climbing fibre input evoked on peripheral stimulation. 3. The topographical organization of the cerebellar cortical projection to the forelimb part of nucleus interpositus anterior was then investigated by systematically mapping the cutaneous tactile and nociceptive 'receptive fields' of the positive field potentials at different sites in the nucleus. Five groups of receptive fields were distinguished and tentatively divided into a total of nineteen subgroups. 4. Each group of receptive fields corresponded to one or two of the previously described receptive field classes of climbing fibres to the C1, C3 and Y zones and was represented in a single area of the nucleus. Within each area there was an orderly representation of different receptive fields. The results suggest that microzones in the C1, C3 and Y zones with similar climbing fibre input project to a common set of neurones in nucleus interpositus anterior. 5. We propose a modular organization for the cerebellar control of forelimb movements through the rubrospinal tract. Each module would consist of a set of neurones in nucleus interpositus anterior and their afferent microzones in the C1, C3 and Y zones. A module would control a specific group of muscles and receive a homogeneous climbing fibre input related to the movement controlled.

Spread of synaptic activity along parallel fibres in cat cerebellar anterior lobe.

1. Mossy fibre evoked activity in the cerebellar cortex elicited by peripheral electrical stimulation was studied in chloralose anesthetized cats. The distribution of intracortical field potentials in the C3 and D zones was mapped in order to determine if there is a spread of synaptic activity outside the mossy fibre termination area. This area was identified by the presence of short latency synaptic field potentials in the granular layer. 2. Molecular layer field potentials were recorded up to 1.5 mm outside the mossy fibre termination area. The latencies of these potentials increased with increasing distance from the mossy fibre termination area, corresponding to a conduction velocity of about 0.4 m/s. 3. Recordings from Purkinje cells, within and outside the mossy fibre termination area, revealed an increase of simple spike activity at latencies corresponding to those of the field potentials in the same location. 4. From the spatial and temporal characteristics of the evoked activity, it is concluded that a mossy fibre input results in spread of synaptic activity along the parallel fibres. 5. The findings are discussed in relation to the recently discovered microzonal organization of the C3 zone. It is proposed that the organization of this zone offers a possibility for the control of muscle synergies, each synergy being represented by a mossy fibre input and the specific set of microzones activated by this input via the parallel fibres.

Distribution of Cutaneous Nociceptive and Tactile Climbing Fibre Input to Sagittal Zones in Cat Cerebellar Anterior Lobe.

Climbing fibres projecting to the cerebellar C3 zone (and the related C1 and Y zones) receive spatially well organized tactile and nociceptive inputs from the skin. In the present study, cutaneous tactile and nociceptive input to climbing fibres projecting to the X, B, C2 and D1 zones in lobule V were investigated in pentobarbitone-anaesthetized cats. From the present results and previous studies, it is concluded that the X, C1, CX, C3 and Y zones receive cutaneous nociceptive climbing fibre input. By contrast, climbing fibres to the B, C2 and D1 zones lack cutaneous nociceptive input. Tactile input was found in all zones. The spatial organization of receptive fields of climbing fibres projecting to the X and D1 zones was similar to that in the C3 zone. They were located on the ipsilateral forelimb, mainly its lateral and distal parts, and their proximal borders were located close to joints. In the B zone, more than half of the receptive fields of climbing fibres were confined to the ipsilateral hind- or forelimb. However, frequently more than one limb and parts of the trunk were included. In the C2 zone, the majority of climbing fibres had distal ipsi- or bilateral receptive fields on the forelimbs, often also including the head/face. Some of the bilateral forelimb receptive fields additionally included the hindlimbs ipsi- or bilaterally. The results indicate that each zone has a characteristic set of climbing fibre receptive fields, which is probably related to its efferent control functions.