SEARCH · PubMed Health

Results for “STIMULATION AND STIMULI”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10Linked to original sources

PubMed1989

Prejunctional modulatory action of neuropeptide Y on peripheral terminals of capsaicin-sensitive sensory nerves.

1. We have determined the effect of neuropeptide Y (NPY) on motor responses produced by activation of capsaicin-sensitive primary afferents in the guinea-pig isolated left atria (reserpine-pretreatment, atropine in the bath) and bronchi (atropine and indomethacin in the bath) using capsaicin itself and electrical field stimulation as stimuli. 2. In both preparations, NPY inhibited or suppressed the response produced by electrical field stimulation while leaving the response to a submaximal concentration of capsaicin unaffected. 3. NPY had no effect on motor responses produced by a submaximal concentration of calcitonin gene-related peptide (atria) or neurokinin A (bronchi), the putative endogenous mediators of the responses produced by activation of the 'efferent' function of sensory fibres in these preparations. 4. We conclude that NPY exerts a prejunctional inhibitory action on transmitter release from peripheral endings of capsaicin-sensitive nerves. Failure of NPY to modulate responses activated by capsaicin provides further evidence for the existence of two independent modes of activation of the 'efferent' function of capsaicin-sensitive sensory nerves.

Animals↗

PubMed1991

Prejunctional modulatory action of neuropeptide Y on responses due to antidromic activation of peripheral terminals of capsaicin-sensitive sensory nerves in the isolated guinea-pig ileum.

1. The effect of neuropeptide Y (NPY) on motor responses produced by activation of capsaicin-sensitive primary afferents in the guinea-pig isolated ileum was determined by use of capsaicin itself and electrical mesenteric nerve stimulation as stimuli. 2. NPY inhibited or suppressed the cholinergic contractile response produced by electrical mesenteric nerve stimulation while leaving the contractile response to a threshold concentration of capsaicin. 3. NPY had no effect on motor responses produced by a submaximal concentration of substance P, the putative endogenous mediator of the 'efferent' function of sensory fibres in this preparation. 4. It is concluded that NPY exerted a prejunctional inhibitory action on transmitter release from peripheral endings of capsaicin-sensitive nerves at interneuronal synapses.

Animals↗

PubMed1970

The proprioceptive reflex control of the intercostal muscles during their voluntary activation.

1. A quantitative study has been made of the reflex effects of sudden changes in mechanical load on contracting human intercostal muscles during willed breathing movements involving the chest wall. Averaging techniques were applied to recordings of electromyogram (EMG) and lung volume, and to other parameters of breathing.2. Load changes were effected for brief periods (10-150 msec) at any predetermined lung volume by sudden connexion of the airway to a pressure source variable between +/- 80 cm H(2)O so that respiratory movement could be either assisted or opposed. In some experiments airway resistance was suddenly reduced by porting from a high to a low resistance external airway.3. Contracting inspiratory and expiratory intercostal muscles showed a ;silent period' with unloading which is attributed to the sudden withdrawal from intercostal motoneurones of monosynaptic excitation of muscle spindle origin.4. For both inspiratory and expiratory intercostal muscles the typical immediate effect of an increase in load was an inhibitory response (IR) with a latency of about 22 msec followed by an excitatory response (ER) with a latency of 50-60 msec.5. It was established using brief duration stimuli (< 40 msec) that the IR depended on mechanical events associated with the onset of stimulation, whereas stimuli greater than 40 msec in duration were required to evoke the ER.6. For constant expiratory flow rate and a constant load, the ER of expiratory intercostal muscles increased as lung volume decreased within the limits set by maximal activation of the motoneurone pool as residual volume was approached.7. The ER to a constant load increased directly with the expiratory flow rate at which the load applied, also within limits set by maximal activation of the motoneurone pool.8. For a given load, the ER during phonation was greater than that occurring at a similar expiratory flow rate without phonation when the resistance of the phonating larynx was mimicked by an external airway resistance.9. It is argued that the IR is due to autogenetic inhibition arising from tendon organs and that the ER is due to autogenetic excitation arising from intercostal muscle spindles.10. The initial dominance of inhibition in this dual proprioceptive reflex control was not predicted by the servo theory. It is proposed that the reflex pathways subserving autogenetic inhibition are under a centrifugal control which determines in relation to previous experience (learning) the conditions under which autogenetic facilitation is allowed.

Airway Resistance↗

PubMed1984

Effects of morphine and indomethacin on evoked neuronal responses of ventrobasal thalamic neurones: site of action of analgesic drugs in adjuvant arthritic rats.

A single neuronal activity was recorded extracellularly in the ventrobasal (VB) nucleus of the thalamus in adjuvant arthritic rats under urethane anesthesia (1200 mg/kg, i.p.). The effects of morphine and indomethacin on the evoked responses elicited by noxious stimuli (transcutaneous electrical stimulation and tibial nerve electrical stimulation) and/or non-noxious stimuli were investigated. Intravenous administration of morphine and indomethacin depressed the evoked responses elicited by either transcutaneous electrical stimulation or tibial nerve electrical stimulation without affecting any background activities. By contrast, the responses of all neurones investigated responding to non-noxious stimuli were never depressed by the intravenous administration of morphine and indomethacin. Morphine showed the same depressant effects on the evoked responses activated by both noxious stimuli, but the depressant effects due to indomethacin on the evoked discharges were more sensitively produced by transcutaneous electrical stimulation than tibial nerve electrical stimulation. Depressant effects of morphine were restored by intravenous naloxone administration, but not observed in case of indomethacin. These results suggest that an analgesic mechanism of morphine and indomethacin may reside in the neo-spinothalamic projection system of adjuvant arthritic rats and that the site of action of indomethacin may also reside in a peripheral site. However, the mode of the central action of indomethacin was different from that of morphine.

Analgesics↗

PubMed1989

The effect of thalamic stimulation in processing of verbal stimuli in dichotic listening tasks: a case study.

In dichotic listening tasks, the (dominant) right ear's superiority in processing verbal stimuli has been attributed to its direct anatomic connection with the left dominant hemisphere. The role played by extralinguistic factors, such as attention and functional tuning of the associated cortical structures, has not been carefully examined. This investigation was undertaken to evaluate the effects of the left thalamic electric stimulation on the processing (recognition and recall) of dichotically presented CVC verbal stimuli in a patient being treated for chronic pain. We report the positive effects of electric stimulation (confirmed by increased subcortical metabolic activity using SPECT, a brain imaging technique) on the processing of dichotically presented verbal stimuli.

Attention↗

PubMed1982

Dual effects of catecholamines on pre- and post-junctional membranes in the dog trachea.

1 Effects of noradrenaline or isoprenaline on the membrane and contractile properties of the smooth muscle cell, or on the excitatory neuro-effector transmission in the dog trachea, in vitro, were observed by use of microelectrodes and double sucrose gap methods.2 Noradrenaline (<5 x 10(-6) M) or isoprenaline (<5 x 10(-7) M) modified neither the membrane potential nor the membrane resistance. Increased concentrations of noradrenaline (>5 x 10(-5) M) depolarized and isoprenaline (>5 x 10(-7) M) hyperpolarized the membrane, and these actions were suppressed by phentolamine and propranolol respectively. Both catecholamines reduced the membrane resistance.3 Noradrenaline (5 x 10(-6) M) or isoprenaline (5 x 10(-7) M) reduced the resting tension, raised the mechanical threshold required to produce the contraction and suppressed the amplitude of phasic contractions evoked by electrical depolarization of the membrane.4 The action potential evoked by an outward current pulse in the presence of tetraethylammonium (TEA) was not affected by 5 x 10(-6) M isoprenaline, while the mechanical response was markedly suppressed.5 The excitatory junction potential (e.j.p.) evoked by electrical field stimulation was blocked by atropine. Noradrenaline (5 x 10(-7) M) or isoprenaline (5 x 10(-8) M) suppressed the amplitude of e.j.p. with no change in the membrane potential or input membrane resistance. Depression in the amplitude of e.j.ps produced by noradrenaline or isoprenaline reduced the amplitude of phasic contractions evoked by e.j.ps.6 These inhibitory actions of the catecholamines on mechanical responses and on e.j.ps were suppressed by pretreatment with propranolol (4 x 10(-6) M).7 Dog tracheal smooth muscles are innervated by cholinergic excitatory and adrenergic inhibitory systems. Electrical field stimulation produced excitation of both cholinergic and adrenergic nerve fibres, and propranolol (4 x 10(-6) M) enhanced the amplitude of e.j.p. generated by excitation of cholinergic nerves when repetitive stimulation (10 stimuli at 20 Hz) was used, but not the amplitude of the e.j.p. evoked by a single stimulus.8 5-Hydroxytryptamine (6 x 10(-6) M) produced a tonic contracture of the dog trachea. After pretreatment with atropine (4 x 10(-6) M), field stimulation (50 mus in duration and repetitive stimuli at 20 Hz) induced reversal of the contracture induced by 5-hydroxytryptamine and this was abolished by propranolol (5 x 10(-6) M).9 These results indicate that endogenous or exogenous catecholamines, in relatively low concentrations, predominantly activate beta-adrenoceptors in the pre- and post-junctional membrane in the dog trachea, and induce muscle relaxation.

Animals↗

PubMed1985

Attempts to suppress tinnitus with transcutaneous electrical stimulation.

Various electrical stimuli were tested for their ability to suppress or relieve severe tinnitus. Stimulation was applied transdermally by electrodes placed on the preauricular and postauricular regions and on the two mastoids. Of the 50 patients tested, only 14 (28%) obtained relief that met the criterion of a reduction in the tinnitus by 40% or more. When relief was obtained, it usually extended for several hours into the poststimulation period. There was only one positive response (2%) in the placebo trial, which was administered to all patients. It was concluded that transdermal electrical stimulation such as that used in this research is not a practical therapeutic procedure for the relief of tinnitus.

Clinical Trials as Topic↗

PubMed2000

Influence of pulse configuration and direction of coil current on excitatory effects of magnetic motor cortex and nerve stimulation.

UNLABELLED: This paper describes the influence of pulse configuration and current direction on the excitation of the hand-associated motor cortex and the median nerve by magnetic stimulation. Monophasic and biphasic current pulses with the same peak rise time of 80 micros and a maximum rate of current change (dI/dt) were discharged through an eight-shaped coil of the stimulator used (Dantec MagPro). Two current directions with opposite orientation in the coil axis were studied. FINDINGS: (1) for both, cortex and nerve stimulation, biphasic stimuli were more effective and elicited compound muscle action potentials (CMAPs) with lower thresholds and larger amplitudes. (2) Using biphasic pulses the direction of the currents in the first phase of the pulse did not influence the CMAP amplitude. (3) Using monophasic pulses induced currents oriented postero-anteriorly in the motor cortex or orthodromically along the nerve axis elicited larger CMAPs than currents in the opposite orientation. (4) Pulse configuration did not influence the CMAP-latencies and by this the stimulation site (cortex, nerve). CONCLUSION: Monophasic stimuli are useful to investigate excitation effects which are dependent on the current direction. The application of biphasic stimuli with their stronger excitation effects might be advantageous when patients with high cortical thresholds or deep lying nerves shall be investigated.

Action Potentials↗

PubMed1975

The functional status and columnar organization of single cells responding to cutaneous stimulation in neonatal rat somatosensory cortex S1.

1. An investigation was carried out on single cells in 7 day old rat primary somatosensory cortex, which responded to cutaneous stimulation using mechanical pulses. 3 percent of cells encountered showed stable spontaneous activity, whereas 88 percent were silent in the absence of intentional stimulation. The remainder showed unstable spontaneous activity. In contrast, the great majority of adult cells were spontaneously active in the absence of stimulation, under similar conditions of urethane anaesthesia. 2. The distribution within cortical layers of cutaneously driven cells was similar in adult and 7 day old rats, and similar to that found in adult mammalian cortex by other workers. 3. 7 day old cells showed diminished excitability to cutaneous stimulation with stimuli at intervals below 10-15 sec, whereas adult cells could be successfully repetitively driven with stimuli at intervals of 500 msec. The low ability of the immature cells to follow repetitive cutaneous stimulation is not due to an overall depression of these cells excitability per se. Latencies of unitary responses in these immature cells were about sixfold those found in equivalent cells at maturity. 4. Columnar organization at seven days of age was similar in outline to that of the adult, but much less discrete. Receptive fields were considerably larger at 7 days and evidence is given that this may be due to inadequate surround inhibition. Immature vibrissae-driven units were directionally selective. 5. At 7 days of age, long inter-spike intervals were rare in spontaneously active cells with the result that inter-spike interval histogram distributions (i.h.s.) were approximately normal. Corresponding i.h.s. of adult cells invariably showed skew distributions. 6. Tactile stimulation of centre receptive fields produced an increase in short and long intervals from spontaneously active cells at each age. In contrast to adult cells, the immature cells commonly responded cyclically, with alternating phases of increased and decreased firing rate for periods of up to 3 sec following punctate stimulation. 7. Decrease in spontaneous firing rate, following the first phase of excitation, was profound in 7 day old cells, and implied that inhibitory mechanisms operate at an early age in the rat somatosensory system. These mechanisms also appear to contribute to cyclical activity of 7 day old cells when driven by punctate cutaneous stimulation.

Action Potentials↗

PubMed1986

Activity of ibopamine on some isolated organs.

The pharmacological activity of ibopamine (SB-7505), the 3,4-diisobutyryl ester of N-methyldopamine, was compared with that of epinine (N-methyldopamine) and dopamine on some isolated organs. The results of this study show that ibopamine and epinine exerts a positive inotropic effect on cat papillary muscle by stimulating the cardiac beta 1- and alpha-adrenoceptors; a positive chronotropic effect on cat right atrium by stimulating the cardiac beta 1-adrenoceptors; a relaxing effect on guinea-pig trachea by stimulating beta 2-adrenoceptors; a relaxing effect on rabbit splenic artery pretreated with phenoxybenzamine and contracted with PGF2 alpha by stimulating the DA1 receptors; an inhibitory effect on the vasoconstriction of rabbit ear artery induced by electrical stimuli by stimulating the DA2 receptors. Esterase activation, either by organ or plasma enzymes, appeared to be a prerequisite of ibopamine activity. Suppression of this activity by esterase inhibitors confirmed that the pharmacological responses are related to the formation of epinine. The magnitude and rate of response of some isolated organs to ibopamine appeared to be related to the esterase content of the tissue.

Animals↗

PubMed1984

[Responses and organization of the receptive fields of neurons of the basal optic nucleus of the frog tegmentum during visual stimulation].

Stationary visual stimuli and diffuse light induced mainly excitatory responses of the neurons. Among the neurons responding to visual stimulations many units were the polysensory cells responding also to tactile and sound stimuli. The questions of organization of the tegmental neurons' visual receptive fields, are discussed. Prevalence of large receptive fields has been noted, mainly excitatory those or having an excitatory center and inhibitory periphery.

Animals↗

PubMed1997

Development of electrical rhythmicity in the murine gastrointestinal tract is specifically encoded in the tunica muscularis.

1. Interstitial cells of Cajal (ICCs) have been identified as pacemaker cells in the gastrointestinal (GI) tracts of vertebrates. We have studied the development of ICCs in pacemaker regions and the onset of electrical rhythmicity in the gastric antrum, small bowel and proximal colon of the mouse. 2. ICCs, as detected by c-Kit immunofluorescence, were found during embryogenesis in regions of the GI tract that eventually become pacemaker areas. Prior to birth, these cells were organized into well-structured networks, and by the end of the embryonic period the morphology of ICC networks in pacemaker regions appeared very similar to that observed in adult animals. 3. Electrical rhythmicity was recorded prior to birth (by E18) in the proximal GI tract (stomach and jejunum), and this activity developed to adult-like behaviour within a week after birth. In the ileum and proximal colon rhythmicity developed after birth, and adult-like characteristics were apparent within the first week. 4. Post-junctional responses of smooth muscles to neural inputs could be recorded at birth, and stimulation of intrinsic nerves often led to oscillatory activity resembling slow waves for up to several minutes following brief stimuli. Nerve stimulation augmented spontaneous activity in the proximal portions of the GI tract and elicited rhythmic activity temporarily in quiescent tissues of the distal GI tract. 5. ICCs and rhythmicity developed in an apparently normal manner in tissues isolated at birth and placed in organ culture. These data suggest that the tunica muscularis provides a suitable microenvironment for the development of ICCs and rhythmicity without the need for extrinsic stimuli. 6. Treatment of small intestinal tissues taken from embryos at E15 with neutralizing c-Kit antibodies abolished ICC development and the organization of ICCs into networks that typically occurs during the late embryonic period. Treatment of muscles taken from newborn animals with c-Kit antibodies blocked postnatal development of ICCs, disrupted already established and functional ICC networks, and rendered muscles electrically quiescent. 7. In summary, ICC networks develop in the pacemaker regions of the murine GI tract before birth. Development and organization of ICCs of the myenteric plexus region into networks precedes the development of electrical rhythmicity. Post-natal development of electrical rhythmicity is mainly characterized by enhancement of the amplitude and frequency of slow waves. The development of ICCs and electrical rhythmicity persists in vitro. ICCs appear to be necessary for the initiation of electrical rhythmicity. These findings provide further evidence for the pacemaker role of ICCs.

Animals↗

PubMed1990

[Treatment of postinfarction ventricular tachycardia based on the results of programmed stimulation].

Serial testing of antiarrhythmic agents (group I and III or their combination) by means of programmed pacing using a simple protocol (1-3 premature stimuli during stimulation from the apex of the right ventricle at a rate of 100 [120] and 140/min) and milder criteria of the effectiveness of treatment (does not produce significant ventricular tachycardias of a frequency above 150/min and with a duration longer than 30 s) was performed in 21 patients with significant post-infarction ventricular tachycardia (same definition of significance). Effective treatment was found in serial testing in 17 patients, i.e. in 80%. According to the results of serial test and long-term adherence to treatment the patients were divided into two groups. Group I comprised 14 patients taking effective treatment up to the completion of the investigation and group II, seven patients, where effective treatment was not revealed during testing (4 patients) or was discontinued because of side-effects (3 patients). During long-term follow up (15.2 +/- 13.5 months) no significant ventricular tachycardias or sudden deaths were recorded in group I but in five patients of group II P less than 0.0003). A correct prediction of ventricular tachycardia or sudden death during long-term treatment was made in 19 patients, i.e. 90%. Serial testing of drugs by programmed stimulation is thus, when the above stimulation protocol is used in patients with significant ventricular tachycardia and with a myocardial infarction in the case-history, an effective method leading to a relatively low incidence of serious ventricular arrhythmic attacks.

Aged↗

PubMed1989

Central and peripheral modulation of spontaneous neuronal activity in the caudate nucleus.

The modulatory action of the caudate on the neural activity of the contralateral nucleus was studied in locally anesthetized, paralysed and artificially ventilated cats. This type of preparation was necessary because of a complete suppression of spontaneous spike activity after subanesthetic doses of general anesthesia. Two types of caudate action potential were characterized according to their waveform: biphasic and triphasic spikes, with a predominance of the former. These waveforms appeared to be independent of recording distance; however, their responses were similar to both central and peripheral stimuli. Caudate stimulation modified the spontaneous activity of the majority of the single units recorded within the opposite nucleus. This effect was mainly inhibitory and keeps up certain somatotopic distribution in the rostrocaudal extent of the nucleus. Kainic lesion of the site of stimulation suppressed the responses in the contralateral caudate nucleus, whereas the responses to substantia nigra and precruciate cortex remained unaltered. On the other hand, stimulation of the precruciate cortex opposite to the recording sites always excited the caudate neurons. The responses evoked by stimulation of ipsilateral substantia nigra and of contralateral sciatic nerve followed a similar pattern to those elicited by caudate stimuli. These results suggest a mostly inhibitory effect of the caudate on neuronal activity within the opposite nucleus, which is reinforced by the action of central and peripheral somatosensory inputs.

Action Potentials↗

PubMed1993

Depolarization of group II muscle afferents by stimuli applied in the locus coeruleus and raphe nuclei of the cat.

1. Electrical stimuli applied in the locus coeruleus/subcoeruleus (LC/SC) and raphe nuclei produce a profound depression of transmission in reflex pathways from group II muscle afferents. The present experiments were performed to determine whether presynaptic inhibitory mechanisms contribute to these effects. 2. Changes in the excitability of afferent terminals to electrical stimuli have been used as an indication of primary afferent depolarization (PAD) produced by conditioning stimuli applied within the LC/SC and raphe nuclei and, for comparison, in the nucleus ruber. Group II afferents originating from ankle flexor muscles and terminating in the midlumbar segments were used for testing. 3. Clear changes in excitability were observed in fourteen of nineteen group II fibres in which the effects of conditioning stimuli applied in the LC/SC were tested and in twelve of seventeen fibres in which the effects of stimuli applied within the raphe nuclei were tested. By comparison, only one of the twelve fibres tested with conditioning stimuli applied to the nucleus ruber was found to be influenced. These effects matched those of the same conditioning stimuli on field potentials evoked by group II afferents at the location at which the terminals of group II fibres were stimulated. 4. Stimuli applied in the LC/SC and in the raphe nuclei both produced a mean decrease in threshold stimulus current of 19%. These effects are comparable to those produced by the most effective volleys in peripheral afferent which, in the same fibres, produced a mean decrease in threshold stimulus current of 24%. 5. In all cases (twelve) in which the effects of stimuli applied in the LC/SC and raphe nuclei were tested on the same group II fibre, either both or neither were found to be effective. This strengthens previous indications that some populations of neurones might be activated by stimuli applied in each of these regions of the brain. 6. In contrast to group II afferents, group Ia afferents investigated in the same experiments were only exceptionally affected. Of seven fibres tested with stimuli applied in the LC/SC, six with stimuli applied in the raphe nuclei and seven with stimuli applied in the nucleus ruber, only one fibre showed any clear change in threshold and this was a single fibre which was similarly affected by stimuli in all three sites. 7. It is concluded that presynaptic inhibitory mechanisms contribute to the depression of transmission in spinal reflex pathways from group II muscle afferents produced by stimulation in the LC/SC and raphe nuclei.

Animals↗

PubMed2003

Periaqueductal gray-evoked dorsal root reflex is frequency dependent.

The dorsal root reflex (DRR) is an antidromic action potential originating in the spinal cord that propagates toward the periphery. Given that both GABA(A) and 5-HT(3) receptors are involved in the generation of DRRs and stimulation of the periaqueductal gray (PAG) can induce the release of GABA and serotonin within the spinal cord, we investigated the modulation of DRRs by the PAG descending system. The central end of the cut left L5 dorsal root in adult Sprague-Dawley rats was tested with single fiber recording. Stimulating electrodes were placed in the PAG, sciatic nerve, or transcutaneously across hindpaws. Fifty-seven DRRs were recorded for the effect of PAG stimulation in 19 rats, and 51 DRRs from 26 rats and nine DRRs from seven rats were recorded for an effect of ipsilateral and contralateral peripheral stimulation, respectively. The results were expressed as a percentage of the number of DRRs over the number of stimuli. PAG stimulation at 0.2, 0.5, 5, 20, and 50 Hz produced ratio's of 113.16+/-9.84, 114.54+/-12.22, 24.6+/-3.23, 17.77+/-4.76, and 12.62+/-3.44 (%), respectively. Stimulation at ipsilateral peripheral nerve evoked DRRs of 103.26+/-8.93, 95.27+/-10.57, 37.66+/-7.55, 11.32+/-4.96, and 5.32+/-3.82 (%), respectively. Stimulation of the contralateral peripheral nerve evoked DRRs of 90.88+/-15.59, 44.30+/-10.77, 6.29+/-1.63, 0.45+/-0.19, and 0.29+/-0.15 (%), respectively. Transection at the thoracic spinal level completely eliminated PAG-induced DRRs. In conclusion, both PAG and peripheral stimulation produced DRRs in a frequency dependent manner. Stimulus intensity has no significant effect on DRRs.

Animals↗

PubMed2003

Frequency-dependent, bi-directional plasticity in motor cortex of human adults.

OBJECTIVE: To determine whether the plastic changes induced in human motor cortex by afferent stimulation depend on stimulus frequency. METHODS: Transcranial magnetic stimulation was used to examine changes in corticospinal excitability in 20 subjects before and after combined peripheral (motor point) and central stimulation. Peripheral stimuli were given as either low frequency (3 Hz) or high frequency (30 Hz) trains. RESULTS: Low frequency stimulation induced prolonged depression of corticospinal excitability, while high frequency stimulation induced prolonged facilitation. These effects persisted for approximately 40-50 min after stimulation ceased. CONCLUSIONS: Corticospinal plasticity induced by dual peripheral and central stimulation is bi-directionally-modifiable in the adult human, with the direction of change being frequency-dependent. SIGNIFICANCE: Therapies using peripheral stimulation to alter human motor cortex excitability could be tailored to exploit the differential effects of stimulus frequency on the direction of the excitability change.

Adolescent↗

PubMed2003

Prefrontal cortex transcranial magnetic stimulation does not change local diffusion: a magnetic resonance imaging study in patients with depression.

OBJECTIVE: To determine whether transcranial magnetic stimulation over the left dorsolateral prefrontal cortex produces pathologic changes or leakage of the blood-brain barrier in patients with depression by using apparent diffusion coefficient magnetic resonance imaging. BACKGROUND: Transcranial magnetic stimulation is a new technology for noninvasively stimulating the brain. It appears to be a relatively safe technique, with some important exceptions. Its neurobiologic mechanisms of action are poorly understood. One theory to explain its apparent antidepressant effects involves a potential change in local blood-brain barrier settings, allowing passage of peripheral substances directly into brain parenchyma. Knowing whether transcranial magnetic stimulation changes local brain diffusion is important as well from a safety perspective. To test whether transcranial magnetic stimulation changes local brain diffusion, we used apparent diffusion coefficient magnetic resonance imaging in depressed patients undergoing interleaved transcranial magnetic stimulation/functional magnetic resonance imaging over the left prefrontal cortex. METHODS: Within a 1.5 Tesla magnetic resonance imaging scanner, 14 depressed patients were stimulated with a figure-eight transcranial magnetic stimulation coil over the left prefrontal cortex. Apparent diffusion coefficient magnetic resonance imaging was acquired before, and immediately after, 1 Hertz transcranial magnetic stimulation (147 stimuli) intermittently delivered at a motor threshold of more than 7.35 minutes. Phase maps of the transcranial magnetic stimulation magnetic fields were used to guide region-of-interest placement. RESULTS: No significant qualitative apparent diffusion coefficient differences were observed before and after 1 Hertz transcranial magnetic stimulation underneath the coil. CONCLUSIONS: One Hertz transcranial magnetic stimulation over the left dorsolateral prefrontal cortex as applied in this study did not result in pathologic changes or leakage of the blood-brain barrier in patients with depression. If prefrontal transcranial magnetic stimulation at these usage parameters changes local diffusion, it is not an obvious or large effect.

Adolescent↗