Perceptual significance of somatosensory cortical reorganization following peripheral denervation

The functional significance of reorganization in somatosensory cortex following peripheral denervation has not been thoroughly addressed. In this paper, two distinct hypotheses dealing with this issue are discussed. The first is the hypothesis of functional respecification. This influential view suggests that sets of partially deafferented cortical neurons, which respond to new peripheral inputs and acquire new receptive fields, undergo corresponding changes in perceptual meaning. Excitation of these neurons by stimulation of their novel receptive fields is thought to result in a change in referral of sensation from the original (now denervated) skin fields to the newly acquired skin fields. The second hypothesis is that of functional conservation. This equally plausible alternative is that sets of partially deprived neurons, although they respond to novel peripheral inputs, retain their original perceptual meaning. Excitation of these neurons by stimulation of their new receptive fields is thought to evoke sensation formerly mediated by those neurons, and hence is still projected to the original, now denervated skin regions or phantom. Behavioral evidence strongly suggests that cortical reorganization after peripheral denervation does not result in major functional respecification, but that the original perceptual function mediated by those neurons is preserved.     

Immediate and simultaneous sensory reorganization at cortical and subcortical levels of the somatosensory system

The occurrence of cortical plasticity during adulthood has been demonstrated using many experimental paradigms. Whether this phenomenon is generated exclusively by changes in intrinsic cortical circuitry, or whether it involves concomitant cortical and subcortical reorganization, remains controversial. Here, we addressed this issue by simultaneously recording the extracellular activity of up to 135 neurons in the primary somatosensory cortex, ventral posterior medial nucleus of the thalamus, and trigeminal brainstem complex of adult rats, before and after a reversible sensory deactivation was produced by subcutaneous injections of lidocaine. Following the onset of the deactivation, immediate and simultaneous sensory reorganization was observed at all levels of the somatosensory system. No statistical difference was observed when the overall spatial extent of the cortical (9.1 +/- 1.2 whiskers, mean +/- SE) and the thalamic (6.1 +/- 1.6 whiskers) reorganization was compared. Likewise, no significant difference was found in the percentage of cortical (71.1 +/- 5.2%) and thalamic (66. 4 +/- 10.7%) neurons exhibiting unmasked sensory responses. Although unmasked cortical responses occurred at significantly higher latencies (19.6 +/- 0.3 ms, mean +/- SE) than thalamic responses (13. 1 +/- 0.6 ms), variations in neuronal latency induced by the sensory deafferentation occurred as often in the thalamus as in the cortex. These data clearly demonstrate that peripheral sensory deafferentation triggers a system-wide reorganization, and strongly suggest that the spatiotemporal attributes of cortical plasticity are paralleled by subcortical reorganization.     

The cortical somatotopic map and phantom phenomena in subjects with congenital limb atrophy and traumatic amputees with phantom limb pain

The extent of the cortical somatotopic map and its relationship to phantom phenomena was tested in five subjects with congenital absence of an upper limb, four traumatic amputees with phantom limb pain and five healthy controls. Cortical maps of the first and fifth digit of the intact hand, the lower lip and the first toe (bilaterally) were obtained using neuroelectric source imaging. The subjects with congenital upper limb atrophy showed symmetric positions of the left and right side of the lower lip and the first toe, whereas the traumatic amputees with pain showed a significant shift (about 2.4 cm) of the cortical representation of the lower lip towards the hand region contralateral to the amputation side but no shift for the toe representation. In healthy controls, no significant hemispheric differences between the cortical representation of the digits, lower lip or first toe were found. Phantom phenomena were absent in the congenital but extensive in the traumatic amputees. These data confirm the assumption that congenital absence of a limb does not lead to cortical reorganization or phantom limbs whereas traumatic amputations that are accompanied by phantom limb pain show shifts of the cortical areas adjacent to the amputation zone towards the representation of the deafferented body part.     

Phantom experiences in mental defective amputees.

The assumption that mental defectives do not experience the phenomenon of "phantom limb" was tested. The results rejected the assumption. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The prevalence of phantom limb experience in amputees.

Reviewed the records of 716 amputees who utilized Canadian prosthetic facilities to determine the prevalence of phantom limb pain or sensation and the possible influence of demographic variables on their presence. The prevalence of phantom pain (62.4%) and phantom sensation (84.1%) tended to confirm recent surveys in other nationalities. Years since amputation was the only variable found to influence the report of either pain or sensation. Ss who lost their limbs prior to 1960 reported significantly more pain (73.3%) than Ss who lost their limbs after 1976 (51.1%). There was also a slight tendency for older Ss to report phantom limb pain more often than younger Ss. Findings suggest that the incidence of phantom limb pain is declining. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Late outcome of amputees with premature atherosclerosis

Plasma free T4 (FT4) concentrations could be increased during hemodialysis in patients with chronic renal failure (CRF) because an increase in non-esterified fatty acids (NEFA) could interfere with the binding of T4 to thyroxine-binding globulin. To evaluate the effect of hemodialysis on the FT4 concentration in patients with CRF, we measured the FT4 in 39 patients with CRF by four assay methods including equilibrium dialysis, the 125I-T4 analog method and enzyme immunoassay. The addition of the fatty acid sodium oleate to normal pooled sera led to a marked increase in FT4 as measured by equilibrium dialysis (Model FT4). A moderate increase in the serum FT4 concentration also was observed with an IMX enzyme immunoassay kit, whereas the Coat-A-Count analog method demonstrated no interference by sodium oleate. The mean serum FT4 prior to hemodialysis measured by equilibrium dialysis did not differ significantly from that in the normal control, although those measured by analog methods (Coat-A-Count and Amerlex) and IMX were subnormal. The FT4 by IMX were albumin-dependent, and the values decreased as the samples were serially diluted, but Model FT4 was not affected by the albumin level or the serial dilution. FT4 by Model FT4 showed a marked increase beginning 10 min after the start of dialysis, and it correlated well with the plasma concentration of NEFA and the NEFA/albumin molar ratio. The other three assay methods, including one which is not affected by NEFA, did not show a change in FT4 at 10 min, but a significant increase of 11 to 17% was observed by the end of dialysis. The TSH concentration decreased significantly during hemodialysis. These data suggest that (1) the low serum FT4 in hemodialysis patients measured by some immunoassay methods may be an underestimation due to the low albumin level; (2) FT4 actually increases during hemodialysis due to the actual increase in NEFA, although the marked increase in FT4 during hemodialysis as measured by equilibrium dialysis is an overestimation due to the in vitro generation of NEFA; and (3) one should beware of aberrations in thyroid hormone parameters during hemodialysis and potential complications.     

Extended and telescoped phantom limbs in unilateral amputees.

The incidence of extended (same length) and telescoped phantom limbs was studied by interview in 239 adult unilateral amputees, above and below elbow and knee (AE, BE, AK, BK). Differences were analyzed by nonparametric statistics. Conclusions were as follows: (a) AEs reported the greatest, and BKs the smallest proportions of shortened phantoms; (b) BE and AK groups were approximately similar; (c) telescoped phantoms of proximal amputations were mainly partly telescoped—of distal amputations, fully telescoped; (d) phantom presence, persistence, strength, shortness, and tactile pressure sensitivity were positively related, paralleling the cephalocaudad principle; (e) limb image (established by cortical and learning factors); and (f) intensity of stump cues (dependent on the cephalocaudad gradient, etiology, and sensitization by amputation), affect perception of phantom length and related sensations. (18 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Walking pattern of midfoot and ankle disarticulation amputees

Measurements of the vertical component of ground reaction force (ORF) and dynamic center of pressure (COP) were recorded for five subjects with midfoot level amputations and six with Syme's ankle disarticulation amputations. All of the subjects underwent amputation surgery as a consequence of peripheral vascular disease and diabetes. GRF measurement was accomplished with the F-Scan system (Tekscan, Boston, MA). Each group exhibited a consistent, reproducible pattern of gait. Subjects with Syme's ankle disarticulation initiated initial loading response, i.e., heel strike, with a concentration of GRF in the center of the anatomic heel. COP progressed along the midline to the center of the anatomic forefoot, where GRF was concentrated at push-off. Midfoot amputees initiated loading at the lateral-posterior heel. COP progressed medially to the midline, where it progressed distally to the level of the distal residual limb (proximal metatarsal metaphyses). It then shifted medially under the base of the first metatarsal, where a small concentration of GRF occurred at push-off, similar to the normal foot. These findings explain the decreased magnitude of propulsion seen in midfoot level amputees and may explain the seemingly paradoxical increased metabolic cost of walking observed in midfoot amputees as compared with Syme's ankle disarticulation amputees.     

Prognostic factors in rehabilitation of above knee amputees for vascular diseases

PURPOSE: This study was undertaken to predict rehabilitation potential and prognostic factors of patients undergoing above knee amputation for vascular diseases. METHOD: In a prospective study on 144 patients consecutively admitted to our rehabilitation unit for above knee amputation, multiple regression analyses were used to assess the relationship between nine independent variables and a battery of outcome measures: the Rivermead Mobility Index (RMI) and Barthel Index (BI) effectiveness on discharge, length of hospital stay. Two multiple logistic regressions were performed, using as dependent variable the occurrence of good or partial autonomy in mobility, quantified as RMI scores. RESULTS: Advanced age was the most powerful prognostic factor influencing effectiveness expressed as both mobility (RMI) and BI. Patients aged < 65 years had a greater probability (odds ratio 2.92) of good autonomy in mobility than older patients. The absence of vascular impairment of the residual limb and timely admission to the rehabilitation hospital correlated positively with effectiveness of mobility. CONCLUSIONS: These findings indicate that relevant prognostic factors can be identified at the beginning of rehabilitation treatment.     

Static versus dynamic prosthetic weight bearing in elderly trans-tibial amputees

During the last few years, the working group 'Psychophysiology' of the Association for Methodology and Documentation in Psychiatry (AMDP) discussed the possibility of the establishment of defined EEG modules in psychiatry. It was the aim to create a common data pool in order to be able to have access to larger data sets. The installation of such a common data pool was regarded as an important prerequisite for a future diagnostic application of EEG and EP data in clinical practice. The most relevant arguments are: From a statistical point of view, multivariate investigations can be improved when relatively large data sets are available. Subgrouping of patients is facilitated. Different centers have access to different populations of patients. Furthermore, compliance with the recommendations contributes to a reduction in misunderstanding and false interpretation of other investigators' results. The working group 'Psychophysiology' of the AMDP now recommends EEG modules to be registered in psychiatry. The recommendations are based on investigations using these modules in clinical research and practice as well as several years of discussion within the working group. Four AMDP modules (I-IV) are presented: MI: resting EEG (closed eyes), MII: resting EEG (eyes open), MIII: EEG during videotracking, and MIV: EEG during choice reaction time. Recommendations for additional modules are planned in the near future: MV: EEG during geometry test, MVI: EEG during labyrinth test, and MVII: amplitude stimulus intensity function. MIII-MVI is paralleled by an EEG recording so that psychomotor performance can be measured and EEG data under different activation conditions are available. Compliance with the recommendations guarantees the possibility of access to the common data pool. Computer software is available in Berlin.     

Increased cardiovascular disease mortality rates in traumatic lower limb amputees

We evaluated the 24-year mortality rates of male traumatic lower limb amputees (n = 201) of the Israeli army, wounded between 1948 and 1974 compared with a cohort sample representing the general population (n = 1,832). Mortality rates were significantly higher (21.9% vs 12.1%, p <0.001) in amputees than in controls. Cardiovascular disease (CVD) mortality was the main cause for this difference. The prevalence of selected risk factors for CVD was determined in 101 surviving amputees (aged 50 to 65 years) and a sample of the controls (n = 96) matched by age and ethnic origin. Amputees had higher plasma insulin levels (during fasting and in response to oral glucose loading) and increased blood coagulation activity. No differences were found in rates of current symptoms of ischemic heart disease or of cerebrovascular disease, obesity, hypertension, altered plasma lipoprotein profile, impaired physical activity, smoking, or nutritional habits. Traumatic lower limb amputees had increased mortality rates due to CVD. Surviving amputees had hyperinsulinemia, increased coagulability, and increased sympathetic and parasympathetic responses (described previously). These established CVD risk factors may explain the excess mortality due to CVD in traumatic amputees.     

Mechanisms of motor dysfunction after transient MCA occlusion: persistent transmission failure in cortical synapses is a major determinant

BACKGROUND AND PURPOSE: Failure of prompt motor recovery after spontaneous recirculation or thrombolytic therapy may be due to an unsatisfactory restoration of synaptic activity within cortex and/or blockade of electrical impulses at the severely ischemic subcortical region. METHODS: Afferent, efferent, and synaptic activities were focally examined within the rat sensorimotor cortex by recording the somatosensory-evoked potential (SEP) and motor area response evoked by stimulation of premotor afferents (PmEP) intracortically and the motor-evoked potential (MEP) generated by stimulation of the forelimb area from the brain stem. The effect of ischemia on electrical activity in the cortex and on axonal conduction in the subcortical region was studied differentially by proximal or distal occlusion of the MCA. RESULTS: MEP consisted of direct and indirect waves generated by direct activation of pyramidal axons and indirect excitation of pyramidal neurons via cortical synapses, respectively. MEP, PmEP, and SEP disappeared on proximal occlusion. Following reperfusion after 1 to 3 hours of ischemia, the direct wave of MEP readily recovered but the indirect wave showed no improvement, suggesting a restored axonal conduction but impaired cortical synaptic transmission. The synaptic defect, which also caused a poor recovery in PmEP and SEP and on electrocorticogram, was persistent and detected 24 hours after 1 hour of proximal occlusion. CONCLUSIONS: Our data suggest that motor dysfunction is caused by loss of cortical excitability and blockade of motor action potentials at the subcortical level during ischemia. After brief transient ischemia, axonal conduction readily recovers; however, a persistent transmission failure at cortical synapses leads to motor dysfunction.     

Patellar tendon bearing orthosis--application as adjunctive treatment in healing of lower-limb tissue loss

In order to clarify the possible physiological role of endogenous opioid peptides (EOP), we studied the effect of low doses of naloxone (specific opiate antagonist) on plasma prolactin levels in male rabbits. Five groups of five male rabbits each was injected daily between 8-9 a.m., with naloxone 12.5, 25, 50, 100 and 200 microg/kg/day. An additional group of ten animals was injected with saline solution and considered the control group. Blood samples were taken at baseline before naloxone administration and later at 90 min and 1, 2, 4, 7, 10 days after its administration. Samples were also taken 4 days after stopping naloxone administration (day 14). Plasma prolactin levels were measured by RIA. A significant constant decrease in PRL levels was seen with the 12.5 microg at 90 minutes, while with the remaining doses a progressive decrease was recorded throughout the study.     

Synaptic reorganization in explanted cultures of rat hippocampus

Due to loss of afferent innervation, synaptic reorganization occurs in organotypic hippocampal slice cultures. With extra- and intracellular recordings, we confirm that the excitatory loop from the dentate gyrus (DG) to CA3 and further to CA1 is preserved. However, hilar stimulation evoked antidromic population spikes in the DG which were followed by a population postsynaptic potential (PPSP); intracellularly, an antidromic spike with a broad shoulder or EPSP/IPSP sequences were induced. Synaptic responses were blocked by glutamate receptor antagonists. Stimulation of CA1 induced a PPSP in DG. Dextranamine stained pyramidal cells of CA1 were shown to project to DG. After removal of area CA3, DG's and mossy fibers' (MF) stimulation still elicited PPSPs and EPSP/IPSP sequences in area CA1 which disappeared when a cut was made through the hippocampal fissure. During bicuculline perfusion, hilar stimulation caused EPSPs in granule cells and spontaneous and evoked repetitive firing appeared even after its isolation from areas CA3 and CA1. Collateral excitatory synaptic coupling between granule cells was confirmed by paired recordings. Besides the preservation of the trisynaptic pathway in this preparation, new functional synaptic contacts appear, presumably due to MF collateral sprouting and formation of pathways between areas CA1 and DG.     

Recreational activities of lower extremity amputees: a survey

This study summarizes a detailed questionnaire evaluation of recreational activities participated in by 100 persons with lower extremity amputations. Additional information was obtained from prosthetists and physical therapists. Approximately 60% of the respondents are active in sports. Younger persons of either sex, who have had amputations for congenital deformities or trauma, are most active. Level of amputation does not appear to be a determining factor as to whether amputees participated or not. The most common recreational activities are fishing and swimming. Sports causing the amputee most discomfort are hunting and jogging. The ability to run and jump is the most difficult to achieve. Reasons for non-participation are pain, embarrassment, insufficient training and lack of organized sports programs for the disabled. Fear of further injury or an overprotective family are not inhibiting factors, nor is cost of the prosthesis. Only a few people wear specifically designed recreational prostheses, and only one-third of the amputees believe that their prosthetist is knowledgeable about recreational prostheses, while 40% feel the prosthetist discouraged their own ideas about prosthetic innovations. Therapists also proved inadequate in their knowledge and efforts at preparing the amputee for recreation. The amputees indicate a need for improved prosthetic design, and believe that insufficient information, both verbal and written, was given to them.     

Perceptual concomitants of conceptual reorganization.

Scheerer held that perceptual reorganization occurs as a concomitant of an induced shift in performance on a conceptual sorting test. This study provided an empirical test of Scheerer's claim for a group of mentally retarded Ss. A perceptual test which utilizes the phi phenomenon was administered to 12 retarded Ss who successfully made the shift on the sorting test (the Pass Group) and 12 who did not (the Fail Group). The Pass Group showed evidence of a highly significant perceptual reorganization, whereas no such evidence was found for the Fail Group. These results strongly supported Scheerer's claim, but for a group which he believed incapable of conceptualization and perceptual reorganization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Accelerographic, temporal, and distance gait factors in below-knee amputees

Gait characteristics of 19 patients with a unilateral below-knee amputation were studied. The accelerographic and foot placement method used in this study allowed for simultaneous acquisition of data commonly obtained in the experimental laboratory (acceleration) and data easily gathered in the physical therapy clinic (temporal and distance factors). The following results may be of interest to the clinician: 1) measures of cadence, stride length, and velocity were highly related and the magnitude of these measures was below commonly accepted values for normal; 2) the below-knee amputees spent more time in stance phase on their uninvolved lower extremity than on their involved (prosthetic) extemity; 3) the step length from heel strike of the uninvolved lower extremity to heel strike of the involved (prosthetic) lower extremity was greater and accomplished in less time than the opposite step; and 4) smoothness of the gait pattern and any single temporal and distance factor exhibited low statistical relationships.