scholarly journals Joint cross-correlation analysis reveals complex, time-dependent functional relationship between cortical neurons and arm electromyograms

2014 ◽  
Vol 112 (11) ◽  
pp. 2865-2887 ◽  
Author(s):  
Katie Z. Zhuang ◽  
Mikhail A. Lebedev ◽  
Miguel A. L. Nicolelis
Keyword(s):  
Cortical Neurons ◽  
Cross Correlation ◽  
Cortical Activity ◽  
Emg Activity ◽  
Brain Machine Interfaces ◽  
Dynamic Task ◽  
Cortical Areas ◽  
Arm Reaching ◽  
Cross Correlation Analysis ◽  
Neurophysiological Studies

Correlation between cortical activity and electromyographic (EMG) activity of limb muscles has long been a subject of neurophysiological studies, especially in terms of corticospinal connectivity. Interest in this issue has recently increased due to the development of brain-machine interfaces with output signals that mimic muscle force. For this study, three monkeys were implanted with multielectrode arrays in multiple cortical areas. One monkey performed self-timed touch pad presses, whereas the other two executed arm reaching movements. We analyzed the dynamic relationship between cortical neuronal activity and arm EMGs using a joint cross-correlation (JCC) analysis that evaluated trial-by-trial correlation as a function of time intervals within a trial. JCCs revealed transient correlations between the EMGs of multiple muscles and neural activity in motor, premotor and somatosensory cortical areas. Matching results were obtained using spike-triggered averages corrected by subtracting trial-shuffled data. Compared with spike-triggered averages, JCCs more readily revealed dynamic changes in cortico-EMG correlations. JCCs showed that correlation peaks often sharpened around movement times and broadened during delay intervals. Furthermore, JCC patterns were directionally selective for the arm-reaching task. We propose that such highly dynamic, task-dependent and distributed relationships between cortical activity and EMGs should be taken into consideration for future brain-machine interfaces that generate EMG-like signals.

Single-Neuron Analysis of Human Thalamus in Patients With Intention Tremor and Other Clinical Signs of Cerebellar Disease

2002 ◽  
Vol 87 (4) ◽  
pp. 2084-2094 ◽  
Author(s):  
F. A. Lenz ◽  
C. J. Jaeger ◽  
M. S. Seike ◽  
Y. C. Lin ◽  
S. G. Reich
Keyword(s):  
Neuronal Activity ◽  
Cross Correlation ◽  
Clinical Signs ◽  
Emg Activity ◽  
Phase Lag ◽  
Cerebellar Disease ◽  
Intention Tremor ◽  
Cross Correlation Analysis ◽  
Relay Nucleus ◽  
Cerebellar Tremor

Tremor that occurs as a result of a cerebellar lesion, cerebellar tremor, is characteristically an intention tremor. Thalamic activity may be related to cerebellar tremor because transmission of some cerebellar efferent signals occurs via the thalamus and cortex to the periphery. We have now studied thalamic neuronal activity in a cerebellar relay nucleus (ventral intermediate—Vim) and a pallidal relay nucleus (ventralis oral posterior—Vop) during thalamotomy in patients with intention tremor and other clinical signs of cerebellar disease (tremor patients). The activity of single neurons and the simultaneous electromyographic (EMG) activity of the contralateral upper extremity in tremor patients performing a pointing task were analyzed by spectral cross-correlation analysis. EMG spectra during intention tremor often showed peaks of activity in the tremor-frequency range (1.9–5.8 Hz). There were significant differences in thalamic neuronal activity between tremor patients and controls. Neurons in Vim and Vop had significantly lower firing rates in tremor patients than in patients undergoing thalamic surgery for pain (pain controls). Other studies have shown that inputs to Vim from the cerebellum are transmitted through excitatory connections. Therefore the present results suggest that tremor in these tremor patients is associated with deafferentation of the thalamus from cerebellar efferent pathways. The thalamic X EMG cross-correlation functions were studied for cells located in Vim and Vop. Neuronal and EMG activity were as likely to be significantly correlated for cells in Vim as for those in Vop. Cells in Vim were more likely to have a phase lag relative to EMG than were cells in Vop. In monkeys, cells in the cerebellar relay nucleus of the thalamus, corresponding to Vim, are reported to lead movement during active oscillations at the wrist. In view of these monkey studies, the present results suggest that cells in Vim are deafferented and have a phase lag relative to tremor that is not found in normal active oscillations. The difference in phase of thalamic spike X EMG activity between Vim and Vop may contribute to tremor because lesions of pallidum or Vop are reported to relieve cerebellar tremor.

Development of local horizontal interactions in cat visual cortex studied by cross-correlation analysis

1993 ◽  
Vol 69 (1) ◽  
pp. 40-56 ◽  
Author(s):  
Y. Hata ◽  
T. Tsumoto ◽  
H. Sato ◽  
K. Hagihara ◽  
H. Tamura
Keyword(s):  
Visual Cortex ◽  
Correlation Analysis ◽  
Cortical Neurons ◽  
Cross Correlation ◽  
Visual Response ◽  
Horizontal Distance ◽  
Orientation Preference ◽  
Functional Development ◽  
Cross Correlation Analysis ◽  
Restricted Region

1. To explore the functional development of local horizontal interactions in the primary visual cortex, we carried out cross-correlation analysis of spike trains recorded simultaneously from a pair of neurons separated horizontally by < 1 mm, in kittens ranging in age postnatally from the second to ninth week. 2. Significantly correlated firings were found in 87 pairs of cells among 423 pairs analyzed, and 77 pairs of them were classified into three types on the basis of their functional implications: 1) excitatory interactions, 2) inhibitory interactions, and 3) common inputs to both neurons of the pair from other sources. 3. Common inputs and excitatory linkage were observed even in animals at the second postnatal week, whereas inhibitory linkage was not seen before the fourth week of age. The probability of observing common inputs and inhibitory linkage increased during development, whereas that of excitatory linkage tended to decrease after the sixth week of age. 4. Significant correlation was rarely seen in pairs with horizontal separation > 600 microns in the seventh to ninth week. In the fourth to sixth week of age, however, approximately 30% of the pairs with horizontal separation between 600 and 800 microns were significantly correlated. 5. Cells that were not sensitive for orientation or that lacked a visual response were observed mainly before the sixth week of age. These cells tended to receive excitatory effects from and share common inputs with other orientation-sensitive cells that were located within the horizontal distance of 400 microns. 6. All three types of correlations were observed mostly in cell pairs with preferred orientations that differed < 45 degrees at all ages studied. In the fourth to sixth week, however, the similarity of orientation preference was not strict, and correlated firings were observed even in a pair with orthogonal orientation preferences; whereas in the seventh to ninth week the tuning became sharper. 7. These results suggest that functional interactions between cortical neurons exist but are much less specific with respect to horizontal separation and orientation preference before the sixth week of age, and these interactions become more specific so as to operate between neurons with similar orientation preferences in more restricted region after the seventh to ninth week of age and thus in adulthood.

Cross-Correlation Analysis of Thalamic Neurons and EMG Activity in Parkinsonian Tremor

1985 ◽  
Vol 48 (1-6) ◽  
pp. 305-308 ◽  
Author(s):  
F.A. Lenz ◽  
R.R. Tasker ◽  
H.C. Kwan ◽  
S. Schnider ◽  
R. Kwong ◽  
...  
Keyword(s):  
Correlation Analysis ◽  
Cross Correlation ◽  
Emg Activity ◽  
Thalamic Neurons ◽  
Parkinsonian Tremor ◽  
Cross Correlation Analysis

scholarly journals EEG–EMG coupling as a hybrid method for steering detection in car driving settings

2022 ◽  
Author(s):  
Giovanni Vecchiato ◽  
Maria Del Vecchio ◽  
Jonas Ambeck-Madsen ◽  
Luca Ascari ◽  
Pietro Avanzini
Keyword(s):  
Hybrid Method ◽  
Cross Correlation ◽  
Muscular Activity ◽  
Motor Preparation ◽  
Emg Activity ◽  
Mu Rhythm ◽  
Emg Signal ◽  
Cross Correlation Analysis ◽  
Left And Right ◽  
Car Driving

AbstractUnderstanding mental processes in complex human behavior is a key issue in driving, representing a milestone for developing user-centered assistive driving devices. Here, we propose a hybrid method based on electroencephalographic (EEG) and electromyographic (EMG) signatures to distinguish left and right steering in driving scenarios. Twenty-four participants took part in the experiment consisting of recordings of 128-channel EEG and EMG activity from deltoids and forearm extensors in non-ecological and ecological steering tasks. Specifically, we identified the EEG mu rhythm modulation correlates with motor preparation of self-paced steering actions in the non-ecological task, while the concurrent EMG activity of the left (right) deltoids correlates with right (left) steering. Consequently, we exploited the mu rhythm de-synchronization resulting from the non-ecological task to detect the steering side using cross-correlation analysis with the ecological EMG signals. Results returned significant cross-correlation values showing the coupling between the non-ecological EEG feature and the muscular activity collected in ecological driving conditions. Moreover, such cross-correlation patterns discriminate the steering side earlier relative to the single EMG signal. This hybrid system overcomes the limitation of the EEG signals collected in ecological settings such as low reliability, accuracy, and adaptability, thus adding to the EMG the characteristic predictive power of the cerebral data. These results prove how it is possible to complement different physiological signals to control the level of assistance needed by the driver.

scholarly journals Excess interictal activity marks seizure prone cortical areas and mice in a genetic epilepsy model

2021 ◽  
Author(s):  
William F Tobin ◽  
Matthew Weston
Keyword(s):  
Cortical Neurons ◽  
Cortical Activity ◽  
Epileptic Encephalopathy ◽  
K Channel ◽  
Future Research ◽  
Dorsal Cortex ◽  
Cortical Areas ◽  
Epileptiform Discharges ◽  
Spontaneous Seizures

Genetic epilepsies are often caused by variants in widely expressed genes, potentially impacting numerous brain regions and functions. For instance, gain-of-function (GOF) variants in the widely expressed Na+-activated K+ channel gene KCNT1 alter basic neurophysiological and synaptic properties of cortical neurons, leading to developmental epileptic encephalopathy. Yet, aside from causing seizures, little is known about how such variants reshape interictal brain activity, and how this relates to epileptic activity and other disease symptoms. To address this knowledge gap, we monitored neural activity across the dorsal cortex in a mouse model of human KCNT1-related epilepsy using in vivo, awake widefield Ca2+ imaging. We observed 52 spontaneous seizures and 1700 interictal epileptiform discharges (IEDs) in homozygous mutant (Kcnt1m/m) mice, allowing us to map their appearance and spread at high spatial resolution. Outside of seizures and IEDs, we detected ~46,000 events, representing interictal cortical activity, in both Kcnt1m/m and wild-type (WT) mice, and we classified them according to their spatial profiles. Spontaneous seizures and IEDs emerged within a consistent set of susceptible cortical areas, and seizures propagated both contiguously and non-contiguously within these areas in a manner influenced, but not fully determined, by underlying synaptic connectivity. Seizure emergence was predicted by a progressive concentration of total cortical activity within the impending seizure emergence zone. Outside of seizures and IEDs, similar events were detected in WT and Kcnt1m/m mice, suggesting that the spatial structure of interictal activity was largely preserved. Several features of these events, however, were altered in Kcnt1m/m mice. Most event types were briefer, and their intensity more variable, across Kcnt1m/m mice; mice showing more intense activity spent more time in seizure. Furthermore, the rate of events whose spatial profile overlapped with where seizures and IEDs emerged was increased in Kcnt1m/m mice. Taken together, these results demonstrate that an epilepsy-causing K+ channel variant broadly alters physiology. Yet, outside of seizures and IEDs, it acts not to produce novel types of cortical activity, but rather to modulate its amount. The areas where seizures and IEDs emerge show excessively frequent and intense interictal activity and the mean intensity of an individual's cortical activity predicts its seizure burden. These findings provide critical guidance for targeting future research and therapy development.

Correlations Between Corticomotoneuronal (CM) Cell Postspike Effects and Cell-Target Muscle Covariation

2000 ◽  
Vol 83 (1) ◽  
pp. 99-115 ◽  
Author(s):  
Brian J. McKiernan ◽  
Joanne K. Marcario ◽  
Jennifer Hill Karrer ◽  
Paul D. Cheney
Keyword(s):  
Cortical Neurons ◽  
Cross Correlation ◽  
Emg Activity ◽  
Small Contribution ◽  
Spinal Cord Neurons ◽  
Cell Target ◽  
Cross Correlations ◽  
Forelimb Muscles ◽  
The Cross ◽  
Suppression Effects

The presence of postspike facilitation (PSpF) in spike-triggered averages of electromyographic (EMG) activity provides a useful means of identifying cortical neurons with excitatory synaptic linkages to motoneurons. Similarly the presence of postspike suppression (PSpS) suggests the presence of underlying inhibitory synaptic linkages. The question we have addressed in this study concerns the extent to which the presence and strength of PSpF and PSpS from corticomotoneuronal (CM) cells correlates with the magnitude of covariation in activity of the CM cell and its target muscles. For this purpose, we have isolated cells during a reach and prehension task during which the activity of 24 individual proximal and distal forelimb muscles was recorded. These muscles show broad coactivation but with a highly fractionated and muscle specific fine structure of peaks and valleys. Covariation was assessed by computing long-term (2 s) cross-correlations between CM cells and forelimb muscles. The magnitude of cross-correlations was greater for muscles with facilitation effects than muscles lacking effects in spike-triggered averages. The results also demonstrate a significant relationship between the sign of the postspike effect (facilitation or suppression) and the presence of a peak or trough in the cross-correlation. Of all the target muscles with facilitation effects in spike-triggered averages (PSpF, PSpF with synchrony, or synchrony facilitation alone), 89.5% were associated with significant cross-correlation peaks, indicating positively covarying muscle and CM cell activity. Seven percent of facilitation effects were not associated with a significant effect in the cross-correlation, whereas only 3.4% of effects were associated with correlation troughs. In contrast, of all the muscles with suppression effects in spike-triggered averages, 38.9% were associated with significant troughs in the cross-correlation, indicating an inverse relation between CM cell and muscle activity consistent with the presence of suppression. Fifty-five percent of suppression effects was associated with correlation peaks, whereas 5.6% was not associated with a significant effect in the cross-correlation. Limiting the analysis to moderate and strong facilitation effects, the magnitude of PSpF was correlated weakly with the magnitude of the cell-muscle cross-correlation peak. Nevertheless, the results show that although many CM cell-target muscle pairs covary during the reach and prehension task in a way consistent with the sign and strength of the CM cell's synaptic effects on target motoneurons, many exceptions exist. The results are compatible with a model in which control of particular motoneuron pools reflects not only the summation of signals from many CM cells but also signals from additional descending, sensory afferent, and intrinsic spinal cord neurons. Any one neuron will make only a small contribution to the overall activity of the motoneuron pool. In view of this, it is not surprising that relationships between postspike effects and CM cell-target muscle covariation are relatively weak with many apparent incongruities.

Motor Patterns for Human Gait: Backward Versus Forward Locomotion

1998 ◽  
Vol 80 (4) ◽  
pp. 1868-1885 ◽  
Author(s):  
R. Grasso ◽  
L. Bianchi ◽  
F. Lacquaniti
Keyword(s):  
Time Course ◽  
Cross Correlation ◽  
Gait Cycle ◽  
Human Gait ◽  
Emg Activity ◽  
Ground Reaction Forces ◽  
Motor Patterns ◽  
Cross Correlation Analysis ◽  
Reaction Forces ◽  
Forward Locomotion

Grasso, R., L. Bianchi, and F. Lacquaniti. Motor patterns for human gait: backward versus forward locomotion. J. Neurophysiol. 80: 1868–1885, 1998. Seven healthy subjects walked forward (FW) and backward (BW) at different freely chosen speeds, while their motion, ground reaction forces, and electromyographic (EMG) activity from lower limb muscles were recorded. We considered the time course of the elevation angles of the thigh, shank, and foot segments in the sagittal plane, the anatomic angles of the hip, knee, and ankle joints, the vertical and longitudinal ground reaction forces, and the rectified EMGs. The elevation angles were the most reproducible variables across trials in each walking direction. After normalizing the time course of each variable over the gait cycle duration, the waveforms of all elevation angles in BW gait were essentially time reversed relative to the corresponding waveforms in FW gait. Moreover, the changes of the thigh, shank, and foot elevation covaried along a plane during the whole gait cycle in both FW and BW directions. Cross-correlation analysis revealed that the phase coupling among these elevation angles is maintained with a simple reversal of the delay on the reversal of walking direction. The extent of FW–BW correspondence also was good for the hip angle, but it was smaller for the knee and ankle angles and for the ground reaction forces. The EMG patterns were drastically different in the two movement directions as was the organization of the muscular synergies measured by cross-correlation analysis. Moreover, at any given speed, the mean EMG activity over the gait cycle was generally higher in BW than in FW gait, suggesting a greater level of energy expenditure in the former task. We argue that conservation of kinematic templates across gait reversal at the expense of a complete reorganization of muscle synergies does not arise from biomechanical constraints but may reflect a behavioral goal achieved by the central networks involved in the control of locomotion.

scholarly journals EMG Muscle Activation Pattern of Four Lower Extremity Muscles during Stair Climbing, Motor Imagery, and Robot-Assisted Stepping: A Cross-Sectional Study in Healthy Individuals

2019 ◽  
Vol 2019 ◽  
pp. 1-8 ◽  
Author(s):  
Damaris E. Geiger ◽  
Frank Behrendt ◽  
Corina Schuster-Amft
Keyword(s):  
Motor Imagery ◽  
Cross Correlation ◽  
Stair Climbing ◽  
Emg Activity ◽  
Healthy Individuals ◽  
Robot Assisted ◽  
Tilt Table ◽  
Imagery Condition ◽  
Gastrocnemius Medialis ◽  
Cross Correlation Analysis

Background. Stair climbing can be a challenging part of daily life and a limiting factor for social participation, in particular for patients after stroke. In order to promote motor relearning of stair climbing, different therapeutical measures can be applied such as motor imagery and robot-assisted stepping therapy. Both are common therapy measures and a positive influence on the rehabilitation process has been reported. However, there are contradictory results regarding the neuromuscular effect of motor imagery, and the effect of robot-assisted tilt table stepping on the EMG activation compared to stair climbing itself is not known. Thus, we investigated the EMG activity during (1) a stepping task on the robot-assisted tilt table Erigo, (2) motor imagery of stair climbing, and (3) real stair climbing in healthy individuals for a subsequent study on patients with lower limb motor impairment. The aim was to assess potential amplitude independent changes of the EMG activation as a function of the different conditions.Methods. EMG data of four muscles of the dominant leg were recorded in m. rectus femoris, m. biceps femoris, m. tibialis anterior, and m. gastrocnemius medialis. The cross-correlation analysis was performed to measure similarity/dissimilarity of the EMG curves.Results. The data of the study participants revealed high cross-correlation coefficients comparing the EMG activation modulation of stair climbing and robot-assisted tilt table stepping in three muscles except for the m. gastrocnemius medialis. As the EMG activation amplitude did not differ between motor imagery and the resting phase the according EMG data of the motor imagery condition were not subjected to a further analysis.Conclusion. Robot-assisted tilt table stepping, but rather not motor imagery, evokes a similar activation in certain leg muscles compared to real stair climbing.

Cross-correlation analysis reveals laminar differences in thalamocortical interactions in the somatosensory system

1996 ◽  
Vol 75 (4) ◽  
pp. 1444-1457 ◽  
Author(s):  
M. J. Johnson ◽  
K. D. Alloway
Keyword(s):  
Correlation Analysis ◽  
Cortical Neurons ◽  
Cross Correlation ◽  
Deep Layer ◽  
Sensory Stimulation ◽  
Superficial Layer ◽  
Cortical Layers ◽  
Thalamic Neurons ◽  
Air Jet ◽  
Cross Correlation Analysis

1. Spontaneous and stimulus-induced activity were recorded from corresponding somatotopic representations in the ventroposterolateral nucleus (VPL) of the thalamus and primary somatosensory (SI) cortex of intact, halothane-anesthetized cats. Thalamic and cortical neurons with overlapping receptive fields on the hairy skin of the forelimb were excited by a series of interleaved air jets aimed at multiple skin sites. 2. The laminar locations of 68% (240 of 355) of the neurons recorded in SI cortex were histologically reconstructed and responses of these 240 SI neurons were analyzed with respect to responses recorded from 118 thalamic neurons. Maximum responsiveness during the initial onset (1st 100 ms) of air jet stimulation was similar for neurons distributed throughout all layers of SI cortex (2-4 spikes per stimulus) and did not differ significantly from VPL responses. During the subsequent plateau phase of the stimulus, VPL neurons discharged at a mean rate of 19.0 spikes/ s and neurons in cortical layers II, IIIa, IIIb, and IV discharged at similar rates. Mean responsiveness during the plateau phase of the stimulus was significantly reduced among neurons in cortical layers V and VI and only averaged 7.1 and 3.9 spikes/s, respectively. 3. Responses recorded simultaneously from pairs of thalamic and cortical neurons were analyzed with cross-correlation analysis to determine differences in the incidence and strength of neuronal interactions as a function of cortical layer. Among 421 thalamocortical neuron pairs displaying stimulus-induced responses, 68 neuron pairs exhibited significant interactions during air jet stimulation. A laminar analysis revealed that 28% (45 of 163) of the neurons in the middle cortical layers displayed significant interactions with thalamic neurons, whereas only 14% (13 of 92) of superficial layer neurons and 6% (10 of 166) of deep layer neurons were synchronized with thalamic activity during air jet stimulation. When thalamocortical efficacy for different layers of cortex was plotted as a cumulative frequency distribution, the strongest interactions in the middle cortical layers were twice as strong as interactions involving the superficial or deep cortical layers. 4. More than 70% of stimulus-induced interactions involved thalamic discharges followed by subsequent cortical discharges and the majority of these interactions involved interspike intervals of < or = 3 ms. Nearly 75% (27 of 37) of interactions in the thalamocortical direction that involved cortical neurons in layers IIIb and IV transpired within a 3-ms interspike interval. For interactions with superficial or deep cortical layers, the proportion of thalamocortical interactions transpiring within 3 ms was only 58% (7 of 12) and 33% (2 of 6), respectively. 5. Cross-correlation analysis of spontaneous activity indicated that 124 pairs of thalamic and cortical neurons displayed synchronous activity in the absence of sensory stimulation. A laminar analysis indicated that similar proportions of cortical neurons in each layer were synchronized with thalamic activity in the absence of cutaneous stimulation. Thus 27% (44 of 163) of middle layer neurons, 30% (28 of 92) of superficial layer neurons, and 31% (51 of 166) of deep layer neurons displayed spontaneous interactions with thalamic neurons. The temporal pattern of spontaneous activity was examined with autocorrelation analysis to determine whether neuronal oscillations were essential for coordinating thalamic and cortical activity in the absence of peripheral stimulation. Only 18.5% (23 of 124) of spontaneous interactions between thalamic and cortical neurons were associated with periodic activity, which suggests that thalamocortical synchronization occurs before the constituent neurons begin to oscillate. 6. The influence of sensory stimulation on spontaneous interactions was examined in 31 pairs of thalamic and cortical neurons that exhibited interactions during prestimulus and stimulus in

Thalamocortical interactions in the somatosensory system: interpretations of latency and cross-correlation analyses

1993 ◽  
Vol 70 (3) ◽  
pp. 892-908 ◽  
Author(s):  
K. D. Alloway ◽  
M. J. Johnson ◽  
M. B. Wallace
Keyword(s):  
Cortical Neurons ◽  
Cross Correlation ◽  
Cortical Cell ◽  
Somatosensory System ◽  
Glabrous Skin ◽  
Connection Strength ◽  
Cortical Layers ◽  
Mean Values ◽  
Cross Correlation Analysis ◽  
Granular Layers

1. Isolated extracellular neuronal responses to cutaneous stimulation were simultaneously recorded from corresponding peripheral representations in the ventrobasal nucleus and primary somatosensory cortex of intact, halothane-anesthetized rats. Thalamic and cortical neurons representing hairy skin on the forelimb were activated by hair movements produced by a series of 50 or 100 discrete air jets. A corresponding set of neurons representing the glabrous pads of the hind paw were activated by a similar number of punctate mechanical displacements. 2. Cortical electrode penetrations were histologically reconstructed, and 118 neurons in the glabrous skin representation exhibited cutaneous responses that were categorized into supragranular, granular, or infragranular groups according to their laminar position. Minimum latencies of cortical neurons responding to glabrous skin displacement were analyzed, and significant differences were found in the distribution of minimum latencies for the different cortical layers. Mean values for minimum latencies in the infragranular and granular layers were 15.8 and 16.3 ms, respectively, whereas supragranular neurons were characterized by minimum latencies having a mean of 20 ms. The differences between these groups suggests that stimulus-induced afferent activity reaches infragranular and granular layers before contacting supragranular neurons. Average latencies were also calculated on responses occurring during the 1st 20 trials, but the cortical distributions of these values overlapped considerably, and differences between the laminar groups were not statistically significant. 3. In several recording sites, two cortical neurons were recorded simultaneously, and the response latencies of these matched pairs were often substantially different despite the similarity in laminar position. This result indicates that laminar location is not the only determinant of response latency and that serially organized circuits are distributed within, as well as between, cortical layers. 4. From a sample of 302 neurons exhibiting cutaneous responses within histologically identified regions of thalamus or cortex, a set of 143 pairs of neurons recorded simultaneously from both regions was available for cross-correlation analysis. Significant thalamocortical interactions were found in 38 neurons pairs. Analysis of these significant interactions revealed that thalamocortical connection strength, as measured by neuronal efficacy, was two to four times larger for neuron pairs having the cortical cell in granular layer IV than for neuron pairs having an extragranular layer cortical neuron. There was no difference in thalamocortical connection strength between neuron pairs containing supra- or infragranular cortical neurons. 5. Summed peristimulus time histograms revealed stimulus-locked inhibition of spontaneous activity in 4% (8/195) or cortical and 18% (20/107) of thalamic neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

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