Characteristics of the cortical input of the hippocampus. Functional differences in the lateral and medial entorhinal cortex

Extracellular investigation in unanaesthetized rabbits revealed low reactivity of the lateral entorhinal cortex neurones (lEC, field 28b) to visual and auditory stimuli. Only 25% of cells responded to them by diffuse long-latency reactions, while in medial EC (mEC, field 28a) 70% of neurones responded to these stimuli with short-latency patterned reactions. The neurones of lEC were selectively responsive to different somatosensory stimuli. Among reactions short-latency on-effects were observed. In some cells application of these stimuli switched on rhythmic bursts of spikes (frequency about 3-4 Hz) or regular activity of pacemaker type. The lEC neurones responded by short-latency driving to electrical stimulation of prefrontal cortex, while mEC neurones were responsive to stimulation of posterior non-primary neocortical areas. The data are discussed in the light of recent morphological findings on cortico-cortical connections of EC.     

Behavioral and neural characteristics of short-latency and long-latency conditioned responses in cats.

Studied head movements to a tone to the left ear (conditioned stimulus [CS]) in 6 cats. An attempt was made to differentiate an orienting, short-latency (alpha) response from the long-latency conditioned (delayed) response. The unconditioned stimulus (UCS) was a brain stimulation to the lateral hypothalamus eliciting a specific, stereotypical head movement. These behavioral characteristics of the unconditioned head movement were used for differentiating it from the conditioned short-latency head movement. Paired conditioning and randomly unpaired control sessions (5 daily sessions each) were given in balanced order to each S. Evoked neural responses in the hippocampus and cingulate cortex were recorded simultaneously to compare the time–amplitude characteristics of evoked responses to earlier findings in multiple-unit recordings. The results supported the differentiation of the behavioral responses. The time–amplitude course of the evoked neural responses showed complex changes, appearing as an increase in the negativity during the alpha-response period and as an increase in the positivity during the long-latency period on omitted-UCS (CS-alone test) trials. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Compatibility of motion facilitates visuomotor synchronization.

Prior research indicates that synchronized tapping performance is very poor with flashing visual stimuli compared with auditory stimuli. Three finger-tapping experiments compared flashing visual metronomes with visual metronomes containing a spatial component, either compatible, incompatible, or orthogonal to the tapping action. In Experiment 1, synchronization success rates increased dramatically for spatiotemporal sequences of both geometric and biological forms over flashing sequences. In Experiment 2, synchronization performance was best when target sequences and movements were directionally compatible (i.e., simultaneously down), followed by orthogonal stimuli, and was poorest for incompatible moving stimuli and flashing stimuli. In Experiment 3, synchronization performance was best with auditory sequences, followed by compatible moving stimuli, and was worst for flashing and fading stimuli. Results indicate that visuomotor synchronization improves dramatically with compatible spatial information. However, an auditory advantage in sensorimotor synchronization persists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral studies of sound localization in the cat

Using the magnetic search coil technique to measure eye and ear movements, we trained cats by operant conditioning to look in the direction of light and sound sources with their heads fixed. Cats were able to localize noise bursts, single clicks, or click trains presented from sources located on the horizontal and vertical meridians within their oculomotor range. Saccades to auditory targets were less accurate and more variable than saccades to visual targets at the same spatial positions. Localization accuracy of single clicks was diminished compared with the long-duration stimuli presented from the same sources. Control experiments with novel auditory targets, never associated with visual targets, demonstrated that the cats localized the sound sources using acoustic cues and not from memory. The role of spectral features imposed by the pinna for vertical sound localization was shown by the breakdown in localization of narrow-band (one-sixth of an octave) noise bursts presented from sources along the midsagittal plane. In addition, we show that cats experience summing localization, an illusion associated with the precedence effect. Pairs of clicks presented from speakers at (+/-18 degrees,0 degrees ) with interclick delays of +/-300 microsec were perceived by the cat as originating from phantom sources extending from the midline to approximately +/-10 degrees.     

Discriminative conditioning with different CS–US intervals produces temporally differentiated conditioned responses in the two eyes of the rabbit (Oryctolagus cuniculus).

The conditioned eyeblink response (CR) in rabbits is lateralized to the eye targeted by the unconditioned stimulus (US). However, a contralateral component has been reported during concurrent discriminative conditioning of the two eyes. The authors investigated CRs produced by both eyes during conditioning with 2 different interstimulus intervals (ISIs) in which a short conditioned stimulus (CS) was paired with a US to the left eye and a long CS was paired with a US to the right eye. Whether the 2 CSs were more or less similar (or identical), the short CS produced short-latency CRs in the left eye, whereas the long CS produced long-latency CRs in the right eye. The contralateral responses to a CS trained at one ISI were separable into temporal corollaries of the ipsilateral response (suggesting a bilaterality of the CR) versus those to a CS trained at another ISI (indicating generalization between the CSs). The results indicate that the neuronal substrates subserving CRs of the two eyes involve not only a dominant lateralization but also some avenue of bilaterality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visuospatial properties of ventral premotor cortex

In macaque ventral premotor cortex, we recorded the activity of neurons that responded to both visual and tactile stimuli. For these bimodal cells, the visual receptive field extended from the tactile receptive field into the adjacent space. Their tactile receptive fields were organized topographically, with the arms represented medially, the face represented in the middle, and the inside of the mouth represented laterally. For many neurons, both the visual and tactile responses were directionally selective, although many neurons also responded to stationary stimuli. In the awake monkeys, for 70% of bimodal neurons with a tactile response on the arm, the visual receptive field moved when the arm was moved. In contrast, for 0% the visual receptive field moved when the eye or head moved. Thus the visual receptive fields of most "arm + visual" cells were anchored to the arm, not to the eye or head. In the anesthetized monkey, the effect of arm position was similar. For 95% of bimodal neurons with a tactile response on the face, the visual receptive field moved as the head was rotated. In contrast, for 15% the visual receptive field moved with the eye and for 0% it moved with the arm. Thus the visual receptive fields of most "face + visual" cells were anchored to the head, not to the eye or arm. To construct a visual receptive field anchored to the arm, it is necessary to integrate the position of the arm, head, and eye. For arm + visual cells, the spontaneous activity, the magnitude of the visual response, and sometimes both were modulated by the position of the arm (37%), the head (75%), and the eye (58%). In contrast, to construct a visual receptive field that is anchored to the head, it is necessary to use the position of the eye, but not of the head or the arm. For face + visual cells, the spontaneous activity and/or response magnitude was modulated by the position of the eyes (88%), but not of the head or the arm (0%). Visual receptive fields anchored to the arm can encode stimulus location in "arm-centered" coordinates, and would be useful for guiding arm movements. Visual receptive fields anchored to the head can likewise encode stimuli in "head-centered" coordinates, useful for guiding head movements. Sixty-three percent of face + visual neurons responded during voluntary movements of the head. We suggest that "body-part-centered" coordinates provide a general solution to a problem of sensory-motor integration: sensory stimuli are located in a coordinate system anchored to a particular body part.     

Eye movement as an indicator of sensory components in thought.

This study investigated a claim of the Neuro-Linguistic Programming (NLP) eye movement model, which states that specific eye movements are indicative of specific sensory components in thought. Forty-eight graduates and undergraduates were asked to concentrate on a single thought while their eye movements were videotaped. They were subsequently asked to report if their thoughts contained visual, auditory, or kinesthetic components. Two NLP-trained observers independently viewed silent videotapes of participants concentrating and recorded the presence or absence of eye movements posited by NLP theorists to indicate visual, auditory, or kinesthetic components in thought. Coefficients of agreement (Cohen's K) between participants' self-reports and trained observers' records indicate support for the visual (K?=?.81, p?p?p?     

Stretch reflex and servo action in a variety of human muscles

1. In the long flexor of the thumb the latency of the stretch reflex and of other manifestations of servo action is some 45 msec, roughly double the latency of a finger jerk. 2. Tendon jerks are feeble or absent in the long flexor of the thumb even in subjects with brisk long-latency stretch reflexes in this muscle. This, and other facts, suggests that the nervous mechanism of the tendon jerk is different from that of the stretch reflex. 3. A muscle that has feeble tendon jerks may show a late component in the response to a tendon tap, with a latency similar to that of the long-latency stretch reflex. 4. On the hypothesis that the excess latency of the stretch reflex over that of a tendon jerk is because the stretch reflex employs a cortical rather than a spinal arc, the excess would be expected to be larger in magnitude for the long flexor of the big toe and smaller for the jaw closing muscles. This is confirmed, 5. An alternative hypothesis that the long latency of stretch reflexes in thumb and toe is because they are excited by slow-conducting afferents is made improbable by the finding that stretch reflexes with an equal or greater excess latency are also found in proximal arm muscles. 6. The long-latency stretch reflex in proximal muscles was seen most distinctly in a healthy subject who happened to have feeble or absent tendon jerks. In ordinary subjects there is often a large, short-latency, presumably spinal component of the stretch reflex in proximal muscles; and short-latency responses to halt and release are also seen, The significance of this spinal latency servo action in proximal muscles remains to be explored. 7. The Discussion argues that the available data on conduction time to and from the cerebral cortex are compatible with the hypothesis that the long-latency component of the stretch reflex uses a transcortical reflex arc, and that none of the experiments described in the present paper are inimical to this view.     

Patterns of eye movements during parallel and serial visual search tasks.

In 2 experiments with a total of 24 undergraduates, eye movements were monitored while Ss performed parallel and serial search tasks. In Exp 1a, Ss searched for an "O" among "X"s (parallel condition) and for a "T" among "L"s (serial condition). In the parallel condition of Exp 1b, "Q" was the target and "O"s were distractors; in the serial condition, these stimuli switched roles. Displays contained 1, 12, or 24 stimuli, with both target-present and target-absent trials. RT and eye-movement measures (number of fixations, saccadic error, and latency to move) indicated that search efficiency was greatest in the parallel conditions, followed by the serial condition of Exp 1a and, finally, by the serial condition of Exp 1b. This suggests that eye movements are correlated with the attentional processes underlying visual search. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The gap effect during visual and auditory stimulation using manual responses

Six experiments were conducted in naive human participants to examine any facilitation produced in manual reaction time (RT) by the interposition of a temporal gap between a warning signal and an imperative signal. Peripheral visual stimuli and monoaural auditory stimuli were used as targets. Participants showed a facilitation of RTs to the targets for both auditory and visual stimuli in the five experiments in which RTs were the dependent variable. In addition, the gap effect increased over successive blocks of trials, suggesting learning. RTs were facilitated only when the gap had predictive value and was salient. Using a variable temporal gap or visual warning stimulus did not change the facilitation in RTs. A further experiment demonstrated that the gap can be perceived by the participants. The dissociation between a learned and a non-learned component in the gap effect suggests that the temporal gap induces two independent processes: warning and disengagement of attention.     

Inhibition of return: Effects of attentional cuing on eye movement latencies.

Inhibition of return refers to a bias against attending to and/or detecting visual stimuli at recently attended locations. A total of 57 Ss participated in 5 experiments, in which Ss were slower to initiate eye movements to previously attended locations. Furthermore, there was more inhibition when a peripheral (exogenous) flash signaled the target, compared with when a central (endogenous) arrow cue was used as an imperative stimulus. That pattern suggests that some of the inhibition is due to processes involved in detecting visual stimuli, and some of the inhibition is related to the movement of the eye. Subsequent experiments showed that the eye-movement component of the inhibition is not object-centered and does not move if the previously attended object moves, although the stimulus-detection component is object-centered. Results have implications for visual attention in general and for the link between overt and covert orienting. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sensory dominance in infants: II. Ten-month-old infants' response to auditory-visual compounds.

A series of studies was conducted with 10-month-old infants in which their response to temporally modulated auditory-visual compounds was examined. The general procedure consisted of first habituating the infants to a compound stimulus (consisting of a flashing checkerboard and a pulsing sound) and then testing their response to it by presenting a series of trials where either one or two temporal attributes of the visual, the auditory, or of both components were changed. When the auditory and visual components were temporally identical, during the habituation phase, the infants only encoded the temporal attributes of the auditory component. When the two components were temporally distinct, or when they were identical but when multiple discriminative cues were available, the infants encoded the temporal aspects of both the auditory and the visual components. When the information context was made more complex, the infants' performance deteriorated, but when the salience of the visual component was increased the infants' performance improved. In sum, although the auditory modality can dominate the visual modality at 10 months of age, the visual modality can process temporal information when the temporal relationship of the information in the two modalities is distinct. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal properties of visual motion signals for the initiation of smooth pursuit eye movements in monkeys

1. Our goal was to assess whether visual motion signals related to changes in image velocity contribute to pursuit eye movements. We recorded the smooth eye movements evoked by ramp target motion at constant speed. In two different kinds of stimuli, the onset of target motion provided either an abrupt, step change in target velocity or a smooth target acceleration that lasted 125 ms followed by prolonged target motion at constant velocity. We measured the eye acceleration in the first 100 ms of pursuit. Because of the 100-ms latency from the onset of visual stimuli to the onset of smooth eye movement, the eye acceleration in this 100-ms interval provides an estimate of the open-loop response of the visuomotor pathways that drive pursuit. 2. For steps of target velocity, eye acceleration in the first 100 ms of pursuit depended on the "motion onset delay," defined as the interval between the appearance of the target and the onset of motion. If the motion onset delay was > 100 ms, then the initial eye movement consisted of separable early and late phases of eye acceleration. The early phase dominated eye acceleration in the interval from 0 to 40 ms after pursuit onset and was relatively insensitive to image speed. The late phase dominated eye acceleration in the interval 40-100 ms after the onset of pursuit and had an amplitude that was proportional to image speed. If there was no delay between the appearance of the target and the onset of its motion, then the early component was not seen, and eye acceleration was related to target speed throughout the first 100 ms of pursuit. 3. For step changes of target velocity, the relationship between eye acceleration in the first 40 ms of pursuit and target velocity saturated at target speeds > 10 degrees /s. In contrast, the relationship was nearly linear when eye acceleration was measured in the interval 40-100 ms after the onset of pursuit. We suggest that the first 40 ms of pursuit are driven by a transient visual motion input that is related to the onset of target motion (motion onset transient component) and that the next 60 ms are driven by a sustained visual motion input (image velocity component). 4. When the target accelerated smoothly for 125 ms before moving at constant speed, the initiation of pursuit resembled that evoked by steps of target velocity. However, the latency of pursuit was consistently longer for smooth target accelerations than for steps of target velocity.(ABSTRACT TRUNCATED AT 400 WORDS)     

Changing directions of forthcoming arm movements: neuronal activity in the presupplementary and supplementary motor area of monkey cerebral cortex

1. To understand roles played by two cortical motor areas, the presupplementary motor area (pre-SMA) and supplementary motor area (SMA), in changing planned movements voluntarily, cellular activity was examined in two monkeys (Macaca fuscata) trained to perform an arm-reaching task in which they were asked to press one of two target buttons (right or left) in three different task modes. 2. In the first mode (visual), monkeys were visually instructed to result and press either a right or left key in response to a forth coming trigger signal. In the second mode (stay), monkeys were required to wait for the trigger signal and press the same target key as pressed in preceding trials. In the third mode (shift), a 50 Hz auditory cue instructed the monkey to shift the target of the future reach from the previous target to the previous nontarget. 3. While the monkeys were performing this task, we recorded 399 task-related cellular activities from the SMA and the pre-SMA. Among them, we found a group of neurons that exhibited activity changes related specifically to shift trials (shift-related cells). The following properties characterized these 112 neurons. First, they exhibited activity changes after the onset of the 50-Hz auditory cue and before the movement execution when the monkeys were required to change the direction of forthcoming movement. Second, they were not active when the monkeys pressed the same key without changing the direction of the movements. Third, they were not active when the monkeys received the 50-Hz auditory cue but failed to change the direction of the movements by mistake. These observations indicate that the activity of shift-related cells is related to the redirection of the forthcoming movements, but not to the auditory instruction itself or to the location of the target key or the direction of the forthcoming movements. 4. Although infrequently, monkeys made errors in the stay trials and changed directions of the reach voluntarily. In that case, a considerably high proportion of shift-related neurons (12 of 19) exhibited significant activity changes long before initiation of the reach movement. These long-lasting activities were not observed during the preparatory period in correct stay trials, but resembled the shift-related activity observed when the target shift was made toward the same direction. Thus these activity changes were considered to be also related to the process of changing the intended movements voluntarily. 5. We found another population of neurons that showed activity modulation when the target shift was induced by the visual instruction in visual trials (visually guided shift-related neurons). These neurons were active when the light-emitting diode (LED) guided the forthcoming reach to the previous nontarget but not to the previous target. Therefore their activity was not a simple visual response to the LED per se. A majority of them also showed shift-related activity in shift trials (19 of 22 in monkey 2). 6. Neurons exhibiting the shift-related activity were distributed differentially among the two areas. In the pre-SMA, 31% of the neurons recorded showed the shift-related activity, whereas in the SMA, only 7% showed such an activity. These results suggest that pre-SMA and SMA play differential roles in updating the motor plans in accordance with current requirements.     

Temporal and binaural properties in dorsal cochlear nucleus and its output tract

The dorsal cochlear nucleus (DCN) is one of three nuclei at the terminal zone of the auditory nerve. Axons of its projection neurons course via the dorsal acoustic stria (DAS) to the inferior colliculus (IC), where their signals are integrated with inputs from various other sources. The DCN presumably conveys sensitivity to spectral features, and it has been hypothesized that it plays a role in sound localization based on pinna cues. To account for its remarkable spectral properties, a DCN circuit scheme was developed in which three inputs converge onto projection neurons: auditory nerve fibers, inhibitory interneurons, and wide-band inhibitors, which possibly consist of Onset-chopper (Oc) cells. We studied temporal and binaural properties in DCN and DAS and examined whether the temporal properties are consistent with the model circuit. Interneurons (type II) and projection (types III and IV) neurons differed from Oc cells by their longer latencies and temporally nonlinear responses to amplitude-modulated tones. They also showed evidence of early inhibition to clicks. All projection neurons examined were inhibited by stimulation of the contralateral ear, particularly by broadband noise, and this inhibition also had short latency. Because Oc cells had short-latency responses and were well driven by broadband stimuli, we propose that they provide short-latency inhibition to DCN for both ipsilateral and contralateral stimuli. These results indicate more complex temporal behavior in DCN than has previously been emphasized, but they are consistent with the recently described nonlinear behavior to spectral manipulations and with the connectivity scheme deduced from such manipulations.     

Associative modulation of the orienting response: Distinct effects revealed by hippocampal lesions.

The ability of auditory stimuli to modulate rats' tendency to orient to visual targets was assessed. In Experiment 1, trials where an auditory stimulus (A) signaled one visual array (X) were intermixed with unsignaled presentations of a second array (Y). Comparison of the orienting responses (ORs) to X and Y revealed that A produced a transient (unconditioned) and an emerging (conditioned) disruptive influence on the OR to X. In Experiments 2 and 3, trials where A signaled X were intermixed with others where another auditory stimulus (B) signaled Y. Stimulus A's ability to modulate the OR to X was then assessed by presenting A prior to test arrays containing both X and Y Control rats were more likely to orient to Y than X (Experiments 2 and 3) and rats with excitotoxic lesions of the hippocampus were more likely to orient to X than Y (Experiment 3). These results show that auditory stimuli exert distinct modulatory influences on the OR to visual stimuli with which they are associated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Induction of visual imagery during NREM sleep

In an attempt to induce eye movements (EMs) in non-rapid eye movement sleep, light and sound stimuli were presented to human subjects (at below-waking threshold) during stage 2 sleep. EMs were used as an indicator of ponto-geniculo-occipital (PGO) wave activity. When at least one concurrent EM in response to the stimuli was observed, the subjects were awakened and mentation reports collected. Compared to equivalent control periods with no stimulation, awakenings from the stage 2 stimulation condition showed a higher frequency of visual imagery reports, electroencephalogram alpha activity, and k-complexes. Additional control and stimulation conditions elicited from rapid eye movement sleep awakenings showed no significant differences in the frequency of visual imagery reports. When the amount of alpha activity before stage 2 awakenings from which imagery was reported was compared to that from which imagery was not reported, imagery awakenings showed significantly more alpha. Results can be interpreted as evidence for a link between PGO activity and dreaming in humans or in terms of an arousal-window hypothesis of visual hallucinations.     

Saccade latency toward auditory targets depends on the relative position of the sound source with respect to the eyes

The latency of saccadic eye movements evoked by the presentation of auditory and visual targets was studied while starting eye position was either 0 or 20 deg right, or 20 deg left. The results show that for any starting position the latency of visually elicited saccades increases with target eccentricity with respect to the eyes. For auditory elicited saccades and for any starting position the latency decreases with target eccentricity with respect to the eyes. Therefore auditory latency depends on a retinotopic motor error, as in the case of visual target presentation.     

Responses of visual, somatosensory, and auditory neurones in the golden hamster's superior colliculus

1. The response characteristics of visual, somatosensory, and auditory neurones in the golden hamster's superior colliculus were investigated.2. As has been noted for other mammalian species, a distinct difference between the functional organizations of the superficial and deeper layers of the superior colliculus was observed.3. Neurones in the superficial layers were exclusively visual, with small receptive-fields, and generally did not show response decrements with repeated stimulation. The sizes of the receptive-fields did not vary appreciably as a function of retinal eccentricity.4. In the deeper layers, visual receptive-fields were large, or could not be accurately delimited, and response habituation was often evident. In addition, many cells in the deeper layers of the colliculus responded only to somatosensory stimuli. Far fewer cells, which appeared to be confined to the caudal portions of the colliculus, responded to auditory stimuli. Polymodal cells were also encountered.5. Selectivity to opposing directions of movement was tested for ninety-four visual cells. Using a ;null' criterion, 27.7% of these cells were judged to be directionally selective. A distribution of the preferred directions of these cells showed a significant preference for movement with an upper-nasal component. With a statistical criterion, 60.6% of these cells were considered to show a significant asymmetry in responding to movement in opposing directions.6. Directional selectivity was also tested for ninety-two cells following acute, unilateral, lesions of the visual cortex. For the eighty cells recorded, homolateral to the ablated cortex, 27.5% were judged as directionally selective using the statistical criterion, while 12.5% were selective with the ;null' criterion. Of the twelve cells isolated in the colliculus, contralateral to the lesions, seven were judged as directionally selective with the statistical, and three with the ;null' criterion.7. The effects of visual cortical lesions upon directional selectivity appeared to be confined to cells in the superficial layers of the colliculus. It was suggested that directional selectivity of many cells in the superficial layers of the tectum of the hamster is organized cortically.8. A clear spatial correspondence was observed for the receptive-fields of visual, somatosensory, and auditory neurones.9. As has been suggested for other species, the hamster's superior colliculus appears to play an important role in orienting the animal toward visual, somatosensory, and auditory stimuli.     

P300 potentials evoked by visual stimulation

INTRODUCTION: The P300 potential is a long-latency endogenous component of the event-related potentials to low-probability target stimuli. The same stimulus delivered without cognitive process does not provoke endogenous components; moreover event-related potentials are not dependent of the sensory pathways used for stimulating the subjects. P300 potential is a biological parameter used in scientific investigations in Clinical Neurophysiology, Neurology, Psychophysiology and Psychiatry. The most frequent methodology for obtaining P300 event-related potential is based on the 'odd-ball' paradigm using auditory stimulation. In this revision we analyzed the difficulties of this methodology and we propose to use the visual stimulation in order to obtain well defined P300 potential, based on a better signal to noise ratio and minor overlapping of exogenous and endogenous components of the evoked potentials. The improvement in the quality of the results obtained when comparing with auditory stimulation, it is supposed to facilitate that the use of P300 potential overflows the field of the investigation and permits their extensive use in the clinical practice.