Basis Of Spontaneous Activity Research Articles

Spontaneous neuronal activity distinguishes human dorsal and ventral attention systems.

On the basis of task-related imaging studies in normal human subjects, it has been suggested that two attention systems exist in the human brain: a bilateral dorsal attention system involved in top-down orienting of attention and a right-lateralized ventral attention system involved in reorienting attention in response to salient sensory stimuli. An important question is whether this functional organization emerges only in response to external attentional demands or is represented more fundamentally in the internal dynamics of brain activity. To address this question, we examine correlations in spontaneous fluctuations of the functional MRI blood oxygen level-dependent signal in the absence of task, stimuli, or explicit attentional demands. We identify a bilateral dorsal attention system and a right-lateralized ventral attention system solely on the basis of spontaneous activity. Further, we observe regions in the prefrontal cortex correlated with both systems, a potential mechanism for mediating the functional interaction between systems. These findings demonstrate that the neuroanatomical substrates of human attention persist in the absence of external events, reflected in the correlation structure of spontaneous activity.

Electrical stimulation of thalamic Nucleus Submedius inhibits responses of spinal dorsal horn neurons to colorectal distension in the rat

In 78 halothane-anesthetized rats, we characterized the responses of single neurons in the dorsal horn of L 6–S 1 spinal segments to a noxious visceral stimulus (colorectal balloon distension, CRD), and studied the effects of focal electrical stimulation of Nucleus Submedius (Sm) on these responses using standard extracellular microelectrode recording techniques. A total of 102 neurons were isolated on the basis of spontaneous activity. Eighty (78%) responded to CRD, of which 70% had excitatory and 30% had inhibitory responses. Neurons showed graded responses to graded CRD pressures (20–100 mmHg), with maximum excitation or inhibition occurring at 100 mmHg. Responses to noxious (pinch, heat) and innocuous (brush, tap) cutaneous stimuli were studied in 73 of the spinal dorsal horn neurons isolated. Fifty-seven (78%) of these neurons (46 CRD-responsive and 11 CRD-nonresponsive) had cutaneous receptive fields, of which 35 (61%) were small and ipsilateral, 14 (25%) were large and ipsilateral, 7 (12%) were large or small and bilateral, and 1 (2%) was small and contralateral. Sixty-one percent of these neurons responded to both noxious and innocuous cutaneous stimulation, 35% responded only to noxious stimulation, and 4% responded only to innocuous stimulation. Electrical stimulation (50–300 μA) of the contralateral Sm produced intensity-dependent attenuation of the CRD-evoked activities of most neurons (18/28 of CRD-excited and 7/12 of CRD-inhibited) tested. Sm stimulation produced facilitation of CRD responses of only one neuron (CRD-inhibited). Sm stimulation had no effects on spontaneous activity. These data indicate that Sm may be involved in the descending inhibitory modulation of visceral nociception at the spinal level.

The effect of morphine on responses of nucleus ventroposterolateralis neurons to colorectal distension in the rat

In 71 halothane-anesthetized rats, we characterized the responses of single neurons in the nucleus ventroposterolateralis (VPL) of the thalamus to a noxious visceral stimulus (colorectal balloon distension; CRD) and studied the effects of intravenous morphine on these responses using standard extracellular microelectrode recording techniques. One hundred nine neurons were isolated on the basis of spontaneous activity. Sixty-four (59%) responded to CRD, of which 52 (81%) had excitatory and 12 (19%) had inhibitory responses. Neurons showed graded responses to graded CRD pressures (20–100 mmHg), with maximum excitation or inhibition occurring at 80 mmHg. Responses to noxious (pinch, heat) and innocuous (brush, tap) cutaneous stimuli were studied in 95 of the VPL neurons isolated. Eighty-three of these neurons (48 CRD responsive and 35 CRD nonresponsive) (87%) had cutaneous receptive fields, of which 96% were small and contralateral and 4% were large and contralateral or bilateral. Ninety-four percent of these neurons responded to both noxious and innocuous cutaneous stimulation, and 6% responded to only noxious stimulation. No neurons responded solely to innocuous stimulation. Cumulative doses of morphine (0.125, 0.25, 0.5, 1, and 2 mg/kg, i.v) produced statistically significant dose-dependent attenuation of neuronal responses to CRD. Naloxone (0.4 mg/kg, i.v.) reversed the effects of morphine. Morphine and naloxone had no significant effects on spontaneous activity. These data support the involvement of VPL neurons in visceral nociception and are consistent with a role of VPL in sensory-discriminative aspects of nociception.

The effect of morphine on responses of ventrolateral orbital cortex (VLO) neurons to colorectal distension in the rat

In 49 halothane-anesthetized rats, we characterized the responses of single neurons in the ventrolateral orbital cortex (VLO) to a noxious visceral stimulus (colorectal balloon distension, CRD), and studied the effects of intravenous morphine on these responses using standard extracellular microelectrode recording techniques. One hundred and four neurons were isolated on the basis of spontaneous activity. Fifty-seven (55%) responded to CRD, of which 32% had excitatory and 68% had inhibitory responses. Neurons showed tendencies toward graded responses to graded CRD pressures (20–100 mmHg), with maximum excitation or inhibition occurring at 80 or 100 mmHg, respectively. Responses to noxious (pinch, heat) and innocuous (brush, tap) cutaneous stimuli were studied in 80 of the VLO neurons isolated. Thirty-three (41%) of these neurons (21 CRD-responsive and 12 CRD-nonresponsive) had cutaneous receptive fields, of which 79% were large and bilateral, 18% were small and bilateral, 3% were small and ipsilateral. Ninety-four percent of these neurons responded only to noxious cutaneous stimulation, 6% responded to both noxious and innocuous stimulation. No neurons responded solely to innocuous stimulation. Cumulative doses of morphine (0.0625, 0.125 and 0.25 mg/kg i.v.) produced statistically significant dose-dependent attenuation of neuronal responses to CRD. Naloxone (0.4 mg/kg i.v.) reversed the effects of morphine. Morphine and naloxone had no significant effects on spontaneous activity. These data support the involvement of VLO neurons in visceral nociception.

The effect of morphine on responses of mediodorsal thalamic nuclei and nucleus submedius neurons to colorectal distension in the rat

In halothane-anesthetized rats, we characterized the responses of single neurons in the nuclei of medial thalamus (MT), specifically the mediodorsal thalamic nucleus (MD) and the nucleus submedius (Sm), to a noxious visceral stimulus (colorectal balloon distension, CRD), and studied the effects of intravenous morphine (Mor) on these responses using standard extracellular microelectrode recording techniques. 62 MD and 46 Sm neurons were isolated on the basis of spontaneous activity. 47 of the MD neurons (76%) responded to CRD, of which 70% had excitatory and 30% had inhibitory responses. 38 of the Sm neurons (83%) responded to CRD, of which 89% had excitatory and 11% had inhibitory responses. Responses of MD and Sm neurons excited by CRD were related significantly to distension pressure (20–100 mmHg), with maximum excitation occurring at 60 and 100 mmHg, respectively. MD neurons inhibited by CRD also had graded responses to graded CRD, with maximum inhibition occurring at 80 mmHg. The responses to noxious (pinch, heat) and nonnoxious (tap, brush) cutaneous stimuli were studied in 59 of the MD and 44 of the Sm neurons isolated. 22 of the MD neurons (37%) studied had cutaneous receptive fields, of which 59% were large and bilateral, 41% were small and usually contralateral receptive fields. 55% of these neurons were nociceptive-specific, 45% responded to both noxious and nonnoxious cutaneous stimulation. 29 of the Sm neurons (66%) studied had cutaneous receptive fields, of which 72% were large and usually bilateral, 14% were small and bilateral, 14% were small and contralateral receptive fields. 90% of these neurons were nociceptive-specific, 10% responded to both noxious and nonnoxious stimulation. No MD or Sm neurons responded exclusively to nonnoxious cutaneous stimulation. Mor (0.125, 0.25, 0.5 and 1 mg/kg IV) attenuated MD and Sm neuronal excitatory responses to CRD in a dose-dependent fashion, abolishing evoked activity with a dose of 0.5 mg/kg ( p<0.05) and 1 mg/kg ( p<0.05), respectively. Naloxone (0.4 mg/kg IV) reversed the effects of Mor. Mor and naloxone had no effects on spontaneous activity. These data support the involvement of MD and Sm neurons in visceral nociception, and are consistent with a role of Sm in affective-motivational, and MD in both sensory-discriminative and affective-motivational aspects of nociception.

Spontaneous activity and frequency selectivity of acoustically responsive vestibular afferents in the cat.

1. Recordings were made from single afferent fibers in the inferior vestibular nerve. Firing rates of a substantial portion of the afferents with irregular background activity increased in response to moderately intense tone bursts. 2. Spontaneous activity from acoustically responsive vestibular afferents was statistically analyzed and compared with data from a more widespread sampling of primary afferents in the cat's vestibulocochlear nerve. Acoustically responsive vestibular afferents had interspike interval histograms with modes > 10 ms, coefficients of variation > 0.15, and skews > 0.88. On the basis of spontaneous activity, these afferents were easily distinguishable from cochlear afferents and regular vestibular afferents, but no obvious features differentiated them from other irregular vestibular afferents. 3. The distributions of spike intervals in the spontaneous activity of acoustically responsive vestibular afferents were fitted by Erlang probability density functions describing the second-order interarrival times of a Poisson process initiated after a finite delay (refractory period). 4. Acoustically responsive vestibular afferents had broad, V-shaped tuning curves with best frequencies between 500 and 1,000 Hz, thresholds of > or = 90 dB SPL, and shapes comparable with the tuning-curve "tails" of cochlear afferents. In contrast to cochlear-nerve afferents, acoustically responsive vestibular afferents did not show a strong relationship between spontaneous rate and threshold. 5. We compare the acoustic frequency selectivity of vestibular and cochlear afferents in terms of their functional and evolutionary relationships. Our data and those of others indicate that acoustically responsive vestibular afferents are likely to provide an input to the acoustic activation of the sternocleidomastoid muscle in humans, and they may provide an input to other acoustic reflexes such as the middle-ear-muscle reflexes.

Responses of neurons in ventrolateral orbital cortex to noxious visceral stimulation in the rat

In pentobarbital-anesthetized rats, responses of single neurons in ventrolateral orbital cortex (VLO) to noxious visceral (colorectal distension, CRD) and cutaneous stimulation were recorded. Of 71 neurons identified on the basis of spontaneous activity, 44 responded to CRD. CRD caused inhibition of neuronal activity in 38, facilitation of activity in four and ‘mixed’ responses in two of these cells. Cutaneous receptive fields were identified in 31 CRD-responsive and 10 CRD-non-responsive neurons. Cutaneous receptive fields were large and bilateral. 25 CRD-responsive cells responded only to noxious cutaneous stimulation, six had wide dynamic range responses. Six CRD-non-responsive cells responded only to noxious stimuli, four had wide dynamic range responses. No VLO neuron responded only to innocuous stimuli. These data are consistent with involvement of VLO in visceral nociception, possibly in non-discriminative aspects of nociception.

Characterization of responses of primary somatosensory cerebral cortex neurons to noxious visceral stimulation in the rat

In pentobarbital-anesthetized rats, responses of single neurons in primary somatosensory cortex (SI) to graded noxious visceral (colorectal distention, CRD) and cutaneous stimulation were recorded. One-hundred fifteen SI neurons were identified on the basis of spontaneous activity, 66 of which responded to CRD. CRD resulted in facilitation of neuronal activity in 33% and inhibition of activity in 52% of these cells. Fifteen percent had mixed facilitated/inhibited responses to varying CRD pressures. Cutaneous receptive fields were identified in 71% of CRD-responsive neurons, with low-threshold or wide dynamic range responses in most cases. Nearly all cutaneous receptive fields were small contralateral sites. Responses to CRD were independent of neuronal depth within the cortex. These data support a role of primary somatosensory cerebral cortical neurons in visceral nociception.

キンギョの延髄聴ニューロンの音刺激に対する応答

Responses of single units to sound stimuli were recorded through tungsten microelectrodes from the acoustic region of the medulla oblongata in the goldfish. Characterization of the medulla units was attempted on the basis of spontaneous activity, frequency-threshold curve, and adaptation. 1. Based on the general appearance of spontaneous activity, the single units were classified into four groups characterized respectively by irregular, burst, regular, and non-spon-taneous activities. 2. The units were classified into two types according to their frequency-threshold curves; one had the best frequency at about 600-700 HZ and the other at about 200-300 HZ. Besides those mentioned, some units sensitive to vibration were also detected. 3. Three adaptation patterns, slow, fast, and intermediate, were found in the medulla units. In some units, an alteration of the adaptation pattern was observed depending on sound frequencies. Such a change of the adaptation pattern was not observed in almost all units at various intensities of the sound. 4. Time-required for recovery of units adapted to a continuous stimulus of 60 sec was measured. The units showing the fast adaptation pattern needed a longer recovery time than other units.

A note on the genetic basis of spontaneous activity in the albino rat.

A note on the genetic basis of spontaneous activity in the albino rat.