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M Trulsson

Publications and source records attributed to M Trulsson.

17 recordsLinked to original sources
PubMed2006

Sensory-motor function of human periodontal mechanoreceptors.

Natural teeth are equipped with periodontal mechanoreceptors that signal information about tooth loads. In the present review, the basic force-encoding properties of human periodontal receptors will be presented along with a discussion about their likely functional role in the control of human mastication. Microneurographic recordings from single nerve fibres reveal that human periodontal receptors adapt slowly to maintained tooth loads. Most receptors are broadly tuned to the direction of force application, and about half respond to forces applied to more than one tooth. Populations of periodontal receptors, nevertheless, reliably encode information about both the teeth stimulated, and the direction of forces applied to the individual teeth. Information about the magnitude of tooth loads is made available in the mean firing rate response of periodontal receptors. Most receptors exhibit a markedly curved relationship between discharge rate and force amplitude, featuring the highest sensitivity to changes in tooth load at very low force levels (below 1 N for anterior teeth and 4 N for posterior teeth). Thus, periodontal receptors efficiently encode tooth load when subjects contact and gently manipulate food using the teeth. It is demonstrated that signals from periodontal receptors are used in the fine motor control of the jaw and it is clear from studies of various patient groups (e.g. patients with dental implants) that important sensory-motor functions are lost or impaired when these receptors are removed during the extraction of teeth.

Adaptation, Physiological↗
PubMed2001

Cortical responses to single mechanoreceptive afferent microstimulation revealed with fMRI.

The technique of intraneural microneurography/microstimulation has been used extensively to study contributions of single, physiologically characterized mechanoreceptive afferents (MRAs) to properties of somatosensory experience in awake human subjects. Its power as a tool for sensory neurophysiology can be greatly enhanced, however, by combining it with functional neuroimaging techniques that permit simultaneous measurement of the associated CNS responses. Here we report its successful adaptation to the environment of a high-field MR scanner. Eight median-nerve MRAs were isolated and characterized in three subjects and microstimulated in conjunction with fMRI at 3.0 T. Hemodynamic responses were observed in every case, and these responses were robust, focal, and physiologically orderly. The combination of fMRI with microstimulation will enable more detailed studies of the representation of the body surface in human somatosensory cortex and further studies of the relationship of that organization to short-term plasticity in the human SI cortical response to natural tactile stimuli. It can also be used to study many additional topics in sensory neurophysiology, such as CNS responses to additional classes of afferents and the effects of stimulus patterning and unimodal/crossmodal attentional manipulations. Finally, it presents unique opportunities to investigate the basic physiology of the BOLD effect and to compare the operating characteristics of fMRI and EEG as human functional neuroimaging modalities in an unusually specific and well-characterized neurophysiological setting.

Brain Mapping↗
PubMed2001

Mechanoreceptive afferents in the human sural nerve.

Microneurography was used to characterize 104 low-threshold mechanoreceptive afferents in the human sural nerve. The afferents were readily classified into four types using criteria developed for the glabrous skin of the hand: SA I (31%), SA II (11%), FA I (49%), and FA II (9%). The distribution of fascicle fields and receptive fields of individual afferents on the lateral side of the foot indicates that the glabrous skin portion of the innervation territory of the sural nerve is more densely innervated than the non-glabrous skin portion. The different populations in the glabrous and non-glabrous skin regions were similar regarding proportion of unit types, receptive field sizes, and force thresholds. The receptive field sizes of the type I units of the present sample were about twice the size compared to those of the glabrous hand units, and the force threshold were at least three times higher for three of the unit types (SA I, FA I, and FA II). Given their receptive properties, it is likely that mechanoreceptive afferents in the sural nerve provide rich information about contact patterns between the foot and environment during stance and locomotion.

Action Potentials↗
PubMed1998

Food-holding and -biting behavior in human subjects lacking periodontal receptors.

Previous studies have suggested that information provided by periodontal mechanoreceptors is particularly important for the fine motor control of the mandible, i.e., when humans hold and carefully manipulate food particles between the teeth with low biting forces. In the present study, we further evaluated this hypothesis by comparing the performance of three age- and gender-matched groups of subjects for which the integrity of the periodontal sensory apparatus differed. Specifically, the subjects had either natural teeth (natural group), dental prostheses supported by oral mucosa (denture group), or dental prostheses supported by osseointegrated implants (implant group). Each subject was instructed to hold half a peanut between the upper and lower central incisors for ca. 3 sec, and then to split it. The force applied by the anterior teeth was continuously monitored by a transducer-equipped bar on which the morsel rested. While the peanut was held, the force generated by subjects in the denture and implant groups was more variable and averaged four times that generated by subjects in the natural group. The peanut was split by a distinct, rapid ramp-increase in force that was similar for all three groups. In subjects lacking periodontal receptors, the morsel frequently escaped from the incisal edges during both phases of the task. The results demonstrate a marked disturbance in the control of precisely directed, low biting forces in subjects lacking periodontal receptors and suggest that the receptors play a significant role in the specification of the level, direction, and point of attack of forces used to hold and manipulate food between the anterior teeth. Moreover, other types of mechanoreceptors can not fully compensate for the loss of periodontal receptors.

Aged↗
PubMed1997

Periodic microstimulation of single mechanoreceptive afferents produces frequency-following responses in human EEG.

Dense multichannel recordings of scalp electroencephalogram were obtained in the vicinity of primary somatosensory cortex, time-locked to repetitive train microstimulation of single, physiologically characterized skin mechanoreceptive afferents in the median nerve of a single human subject. Frequency-domain analysis of cross-trial averages for fast-adapting type one and slowly adapting type one afferents revealed prominent, topographically organized "driving" responses in the electroencephalogram at the frequency of stimulation, which vanished under various statistical and experimental control conditions. The responses also exhibited systematic declines in amplitude both across and within trials, and orderly changes in scalp topography as a function of the location of afferents' receptive fields on the hand. The observed response properties are tentatively explained in terms of characteristics of the pattern of afferent drive impressed on the cortex by microstimulation.

Electric Stimulation↗
PubMed1997

Low-threshold mechanoreceptive afferents in the human lingual nerve.

Intrafascicular multiunit activity and impulses in single mechanoreceptive afferents were recorded from the human lingual nerve with permucosally inserted tungsten microelectrodes. Nylon filaments and blunt glass probes were used for mechanical stimulation of the mucosa of the dorsal surface of the tongue. The innervation territories of nine nerve fascicles were mapped during multiunit recordings. All fascicle fields included the tip of the tongue, suggesting a particularly high innervation density for this area. Thirty-three single mechanoreceptive afferents were isolated and studied. Of these afferents, 22 were characterized by very small mucosal receptive fields (range: 1-19.6 mm2; geometric mean: 2.4 mm2) and responded to extremely low mechanical forces (force threshold range: 0.03-2 mN; geometric mean: 0.15 mN). As such, it was concluded that these "superficial" units terminated near the surface of the tongue. The remaining 11 units responded to probing of large areas of the tongue (> 200 mm2) and exhibited high force thresholds (> or = 4 mN). It was concluded that these "deep" units terminated in the muscle mass of the tongue. Fourteen of the superficial units were classified as rapidly adapting and resembled the fast-adapting type I afferents described for the glabrous skin of the human hand. The rapidly adapting units responded both during the application and removal of, but not during maintenance of, the mechanical stimuli on the receptive field. Two types of slowly adapting responses were observed. One type (characteristic of only 2 units) was characterized by a pronounced sensitivity to force change during the application and removal of the mechanical stimuli and an irregular static discharge during maintenance of the stimulus on the receptive field. In contrast, the other six units exhibited a weak sensitivity to force change, a highly regular static discharge, and spontaneous activity. As such, these two types of slowly adapting units resembled the slowly adapting I and II afferents, respectively, described for the hand. All 11 deep units were slowly adapting, and 7 were, in addition, spontaneously active. The units were not equally sensitive to the application and removal of the mechanical stimuli, suggesting at least two different modes of termination in tongue muscle. The deep units reliably encoded information about tongue movements in the absence of direct contact with the receptive field. In contrast, the superficial units responded vigorously when the tongue was moved to bring the receptive field into physical contact with other intraoral structures.

Adult↗
PubMed1996

Forces applied by the incisors and roles of periodontal afferents during food-holding and -biting tasks.

The force exerted by the central incisors while holding and splitting a food morsel was analyzed to characterize human biting behavior. The force was continuously sampled by a transducer-equipped plate upon which a small piece of dry biscuit or half a peanut rested. Subjects were instructed to position the plate between the incisor teeth and to split the morsel either immediately ("split task") or after holding it for a brief period ("hold-and-split task"). While holding either food substance between the incisors, subjects automatically exerted light contact forces of less than 1 N (0.36-0.76N range among subjects). Considering that the subjects had no instructions about what force levels to employ, the hold force was remarkably stable during individual trials and highly similar among trials. Even during the split task, subjects opted to "hold" the morsel momentarily on ca. 50% of the trials with a similar, low contact force. For both tasks, subjects split the morsel by exerting a distinct, rapidly executed ramp increase in force. The split occurred at 7.8-10.3 N (range among subjects) bite force for the biscuit and 16.0-19.0 N for the peanut. The magnitude of the forces used during the hold phase were within the range over which most periodontal afferents are optimally sensitive to changes in force, i.e., forces below about 1 N. This observation suggested that the subjects automatically adjusted the force to maximize the availability of information from periodontal afferents and avoided higher forces at which the sensitivity of most afferents was not optimal. We further confirmed that the periodontal receptors serve a role in controlling the hold force by anesthetizing the periodontal tissues: subjects employed considerably higher and more variable hold forces, but there was no effect on the split phase. In addition, the morsel frequently escaped from the incisal edges of the teeth while the subject attempted to maintain it in position. It was concluded that subjects rely on signals from periodontal afferents to regulate the jaw muscles, particularly when they first contact, manipulate, and hold food substances between the teeth.

Adolescent↗
PubMed1996

Encoding of tooth loads by human periodontal afferents and their role in jaw motor control.

Microneurography has been used to analyze the functional properties of human periodontal mechanoreceptors. Signals were recorded from single afferents in the inferior alveolar nerve while controlled forces were applied to the teeth. We have found that all periodontal afferents adapt slowly to maintained loads. Most afferents are tuned broadly to direction of force application, and about half respond to forces applied to teeth adjacent to the one to which the afferent distributes. Populations of periodontal afferents, nevertheless, reliably encode information about both the teeth stimulated and the direction of forces applied to the individual teeth. Information about the magnitude of steady forces is made available in the mean firing-rate response of periodontal afferents. Most afferents exhibit a marked "hyperbolic" relationship between the static discharge rate and the force amplitude; the highest sensitivity to changes in static force is observed at forces below 1 N. Similarly, the dynamic sensitivity is highest at low forces. These afferents efficiently encode food contact during biting and continuously discharge while food is held between the incisors. Subjects spontaneously exert low contact forces matched to the sensitivity characteristics of these periodontal afferents when holding food substances between the incisors. If periodontal afferent information is not available, the control of the hold forces is severely impaired. Moreover, since only a few afferents encode information about the rapid and strong force increase employed to bite through food, we conclude that subjects rely on signals from periodontal afferents to regulate the jaw muscles primarily when they first contact, manipulate and hold food substances between the teeth. A potential role for periodontal afferents in the spatio-intensive control of jaw actions is discussed.

Humans↗
PubMed1995

Receptor encoding of moving tactile stimuli in humans. I. Temporal pattern of discharge of individual low-threshold mechanoreceptors.

The response of 70 cutaneous, low-threshold mechanoreceptors in the human median, radial and inferior alveolar nerves to well controlled brush stimuli moving across the receptive field was quantitatively studied. Microneurography was used to obtain the response of each to multiple velocities from 0.5 to 32 cm/sec in at least two opposing directions. A high degree of response consistency was observed from the slowly adapting receptors to replication of the same stimulus and to a lesser, but significant degree from the fast adapting receptors. The evoked discharge reflected up to three partially overlapping phases of the moving stimulus: skin compression, indentation, and stretch. Although the overall discharge rate increased with both stimulus velocity and force, the spatial discharge pattern was preserved to a high degrees. In contrast, the discharge patterns differed for opposing and orthogonal directions. Reducing the area of skin surrounding the receptive field that was contacted by the moving stimuli had little effect on the evoked response. Individual mechanoreceptors display highly reliable differences to brush stimuli moving at different velocities. to brush stimuli moving at different velocities. Moreover, different directions of movement evoke differences in the discharge that are consistently observed upon replication of the same stimuli. Despite the richness and consistency in the spatial discharge pattern displayed by individual receptors, it is argued that the details of the patterns are not likely used by the CNS to infer information about direction and velocity of movement across the skin. Rather, the intensity of discharge is proposed as a plausible information-bearing attribute of the stimulus-evoked response.

Adult↗
PubMed1994

Encoding of amplitude and rate of forces applied to the teeth by human periodontal mechanoreceptive afferents.

1. The encoding of force amplitude and force rate by human periodontal mechanoreceptive afferents was studied. Recordings were obtained from 19 single periodontal afferents in the inferior alveolar nerve with the use of tungsten microelectrodes. Loads consisting of a force increase (loading ramp), a phase of maintained force (static phase), and a force decrease (unloading ramp) were applied to the receptor bearing tooth, which was most often an incisor. The static forces applied ranged between 0.05 and 5 N, and the rate of force applied during the loading ramps ranged between 0.4 and 70 N/s. The forces were primarily applied in one of six directions (lingual, labial, mesial, distal, upward, or downward) that evoked the greatest discharge activity. 2. For each force application, the steady-state response was defined as the mean discharge rate during a 1-s period starting 0.5 s after the end of the loading ramp. Most afferents (15/19) exhibited a "hyperbolic" (viz., negatively accelerating) relationship between the amplitude of the stimulation force and the steady-state response, featuring a pronounced saturation tendency: the highest sensitivity to changes in static force was observed at force levels below 1 N. At higher force levels the sensitivity gradually diminished. Moreover, the dynamic sensitivity similarly decreased with increasing amplitude of static background force. For a subsample of afferents studied, comparable stimulus-response relationships were obtained in directions other than the most responsive one, but the discharge rates were lower. 3. In contrast to the response of most afferents, four (4/19) differed in that they consistently exhibited a nearly linear relationship between force amplitude and the steady-state response. Moreover, these afferents maintained their dynamic sensitivity as the amplitude of the background force was increased. 4. The steady-state response of all afferents was well described as a constant times F/ (F + c), where F represents the steady-state force, and c the force generating one-half the estimated maximum discharge rate that could be evoked by steady-state force stimulation. The c-parameter was on average 0.42 N (range 0.05-1.1 N) for the afferents exhibiting hyperbolic stimulus-response relationships. In contrast it ranged between 5 and 22 N for those exhibiting "nearly linear" relationships. A hypothetical model of the mechanics of the periodontal ligament supporting the F/(F + c) transform is proposed. 5. A general transfer function was developed to predict the instantaneous discharge rate of an individual afferent to arbitrary force profiles applied to the receptor bearing tooth.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1993

Multiple-tooth receptive fields of single human periodontal mechanoreceptive afferents.

1. Single-unit impulse activity from 25 mechanoreceptive afferents was recorded in the human inferior alveolar nerve using tungsten microelectrodes. All of these afferents were considered to originate in periodontal receptors because they showed responses to mechanical stimulation of one or more teeth but not to stimulation of the gingiva. 2. For each afferent isolated, forces with "ramp-and-hold"-shaped profiles of similar magnitudes (261 +/- 21 mN, mean +/- SD) were applied to the incisors, the canine, and the first premolar on the recording side, and the contralateral central incisor in four horizontal directions: lingual, labial, mesial, and distal. For a few of the afferents, forces were also applied in the axial directions (up and down). Both static and dynamic response components were analyzed. 3. For about one half of the tested afferents, the receptive fields were restricted to a single tooth. The remainder (52%) responded to stimulation of a group of teeth (on average 3.1 teeth), which typically showed contact between their crowns. 4. Afferents responding to loading of multiple teeth showed their strongest responses to forces applied to a particular tooth, with a gradual decline in the responsiveness to the adjacent teeth. 5. The stimulation directions eliciting the strongest afferent responses for the most sensitive tooth were approximately evenly distributed over the four stimulation directions, except for some bias toward the lingual direction. In contrast, loading of the adjacent teeth most often showed the strongest responses in the mesial or distal directions, in most cases toward the most sensitive tooth.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Directional sensitivity of human periodontal mechanoreceptive afferents to forces applied to the teeth.

1. Single-unit impulse activity from thirty-eight mechanoreceptive afferent fibres was recorded in the human inferior alveolar nerve using tungsten microelectrodes. All afferents responded to mechanical stimulation of the teeth and most likely supplied periodontal mechanoreceptors. 2. All afferents showed their highest sensitivity to forces applied to a particular tooth (the lower incisors, the canine or the first premolar). Forces with 'ramp-and-hold' shaped profiles of similar magnitudes were applied to that tooth in the following six directions: lingual, labial, mesial and distal in the horizontal plane, and up and down in the axial direction of the tooth. Both static and dynamic response components were analysed. 3. All afferents were 'slowly adapting' since they discharged continuously in response to static forces in at least one stimulation direction. Twenty-five afferents (66%) were spontaneously active in the sense that they showed an on-going discharge in the absence of external stimulation. 4. Diverse receptive fields were observed. Most afferents (74%) responded to static forces in two or three of the four horizontal directions. Likewise, all units showed excitatory responses to axial loading with a majority (74%) responding in one of the two axial directions and the remainder in both axial directions. Spontaneously active afferents generally decreased their discharge rate when stimulated in directions opposite to the directions exciting the afferent. With regard to population responses, approximately half of the afferents showed excitatory responses to each stimulus direction except for downwards, in which 86% responded. 5. Twenty-three afferents (61%) exhibited the strongest response to forces in one of the horizontal directions. Of those, a majority were most responsive to the lingual direction (52%) and some to the labial direction (30%). Accordingly, the discharge rates during force application averaged over the whole afferent sample were highest in these directions. Of the remaining afferents, most responsive to one of the axial directions, 60% showed their strongest responses to forces in the downward direction. 6. Forty-five per cent of the afferents showed wider receptive fields to the dynamic component of the force stimulation than to the static. The direction of maximal sensitivity, however, remained the same with few exceptions. 7. It was demonstrated that even though individual periodontal mechanoreceptive afferents provide ambiguous information regarding the direction of a force applied to a tooth, populations of such afferents are well suited to give detailed directional information. It is suggested that such information may play an important role for the control of mastication.

Adult↗
PubMed1988

Mechanoreceptor activity from the human face and oral mucosa.

The feasibility of adopting the microneurography technique (Vallbo and Hagbarth 1968) as a tool to investigate the mechanoreceptive innervation of peri- and intra-oral tissues was explored. Multi-unit activity and impulses in single nerve fibers were recorded from the infraorbital nerve in healthy volunteers. The innervation territories of individual nerve fascicles were mapped. These varied considerably but most fascicle fields comprised the corner of the mouth. Twenty-four single mechanoreceptive units were recorded. Eighteen innervated the skin of the face, and six innervated the mucous membranes of the lips or cheeks. A majority of the mechanoreceptive afferent units were slowly adapting with small and well defined receptive fields. It is suggested that the various slowly adapting responses may originate from two different types of afferent units. No afferents showed response properties similar to typical Pacinian-corpuscle afferents.

Action Potentials↗
PubMed1988

Mechanoreceptive afferent activity in the infraorbital nerve in man during speech and chewing movements.

The method of microneurography was used to record activity in trigeminal cutaneous and mucosal mechanoreceptive afferents during natural orofacial behaviors such as speech gestures, chewing, licking and swallowing. Multi-unit activity and impulses in single nerve fibers were recorded from the infraorbital nerve. It appeared that these mechanoreceptors respond to contact between the lips, air pressures generated for speech sounds, and to the deformation/strain changes of the facial skin and mucosa associated with various phases of voluntary lip and jaw movements. The relatively vigorous discharge of cutaneous and mucosal afferents during natural movements of the face are consistent with the claim that mechanoreceptors found within the facial skin provide proprioceptive information on facial movements.

Action Potentials↗