Biomedical subjects

Hossein Esteky

Publications and source records attributed to Hossein Esteky.

10 recordsLinked to original sources

PubMed2006

Microstimulation of inferotemporal cortex influences face categorization.

The inferior temporal cortex (IT) of primates is thought to be the final visual area in the ventral stream of cortical areas responsible for object recognition. Consistent with this hypothesis, single IT neurons respond selectively to highly complex visual stimuli such as faces. However, a direct causal link between the activity of face-selective neurons and face perception has not been demonstrated. In the present study of macaque monkeys, we artificially activated small clusters of IT neurons by means of electrical microstimulation while the monkeys performed a categorization task, judging whether noisy visual images belonged to 'face' or 'non-face' categories. Here we show that microstimulation of face-selective sites, but not other sites, strongly biased the monkeys' decisions towards the face category. The magnitude of the effect depended upon the degree of face selectivity of the stimulation site, the size of the stimulated cluster of face-selective neurons, and the exact timing of microstimulation. Our results establish a causal relationship between the activity of face-selective neurons and face perception.

Aging↗

PubMed2006

Visual spatial integrity in the absence of splenium.

Several lines of evidence have confirmed that visual integrity among the two hemifields is severely impaired following transection of posterior part of the corpus callosum (splenium). But the extent of this impairment differs for various visual functions. Here, in a posterior callosectomized patient (MD), interhemispheric visual spatial integrity is investigated in three experiments. In the first experiment, MD was asked to make decision about horizontal alignment of two balls presented simultaneously in one of three conditions: both in right or left hemifield, or each in one hemifield. We have previously shown that she is not able to perform a shape-matching task for stimuli presented to different hemifields. But in this task, MD was able to compare location of the two bilaterally presented stimuli significantly above chance level. Then we investigated whether attentive visual object tracking across vertical meridian of the visual field is possible in the absence of splenium. MD had to attentively track one bouncing ball among three identical balls, while it crossed the vertical midline in half of trials. Her performance in crossed conditions was significantly above chance level, but it was lower than uncrossed conditions. Finally, we investigated the contribution of simple interhemispheric temporal signals in performing the attentive tracking task. Results suggest that the patient was not using such temporal signals. Our results suggest that interhemispheric connections other than splenium can contribute in making an integral visual map across hemifields. Such an integrated map can be used for bilateral visual spatial comparisons and visual spatial attention.

Adult↗

PubMed2005

Effects of neonatal C-fiber depletion on neocortical long-term potentiation and depression.

Capsaicin (Cap)-induced depletion of C-fiber afferents results in plasticity of somatosensory system which is manifested as a functional alteration at different levels of the somatosensory pathway. In the present study we examined the effect of Cap-induced neonatal depletion of C-fibers on the induction of long-term potentiation (LTP) and long-term depression (LTD) in the neocortex of freely moving rats. A stimulating electrode was implanted into corpus callosum and a recording electrode was implanted in the somatosensory cortex of control (Con: normal, without electrical stimulation), trained (normal, with electrical stimulation) and Cap-treated (C-fiber depleted, with electrical stimulation) adult rats. Two weeks after the surgery, evoked field potential responses were recorded before, during (12 days) and after (1 month) the induction period of LTP and LTD. The LTP and LTD response characteristics during the time course of recording were compared between different groups. In the train group, LTP and LTD appeared after 3 days of stimulation. LTP magnitude peaked after about 6 days while LTD magnitude peaked in about 12 days. C-fiber depletion postponed the development of LTP and LTD making the highest differential levels of LTP about 6 days after the initiation of LTP induction. The impact of C-fiber depletion on slowing the time course of LTD induction was more prolonged and lasted until day 12 of the initiation of LTD induction. These results suggest that intact C-fibers are necessary for normal plasticity and long-term synaptic modification of the somatosensory system.

Animals↗

PubMed2005

Effects of GABAA receptor inhibition on response properties of barrel cortical neurons in C-fiber-depleted rats.

C-fiber depletion results in expansion of low threshold somatosensory mechanoreceptive fields. In this study, we investigated the role of intact C-fibers in GABAA-mediated inhibition in barrel cortical neurons. We used electronically controlled mechanical stimulation of whiskers to quantitatively examine the responses of barrel cells to whisker displacements. After systemic injection of picrotoxin neuronal responses were recorded at 5 min intervals for 20 min and then at 10 min intervals for 100 min. Picrotoxin injection caused a 3-fold increase in response magnitude of adjacent whisker stimulation and 1.4-fold increase in response magnitude of principal whisker stimulation with a maximum enhancement 50 min after the injection. There was no significant change in spontaneous activity following picrotoxin injection. The response enhancement and receptive field expansion observed in normal rats were completely absent in the C-fiber-depleted rats. These results suggest that the GABAA-mediated inhibition that modulates the receptive field functional organization of the barrel cortex depends on intact C-fibers.

Animals↗

PubMed2005

Configural and analytical processing of familiar and unfamiliar objects.

Configural processing could develop for non-face visual objects as one becomes familiar with those objects through repeated exposure. To explore the role of familiarity in object recognition, we studied the effect of adaptation to a visual object (adapting stimulus) on the identification performance of other objects (test stimulus) while adapting and test stimuli were exactly the same, shared parts or were completely different. We used a subset of English alphabets (p, q, d and b) as familiar objects and an unfamiliar set of symbols constructed from same parts but with different configurations. Adaptation to a member of each set led to a lower identification performance for that object in a crowding paradigm. Adaptation to each member of the unfamiliar set resulted in decreased identification performance for the same object and those members of the set that shared parts with the adapting stimulus. But no such transfer of adaptation was observed for the familiar set. Our results support the notion that processing of object parts plays an important role in the recognition of unfamiliar objects while recognition of familiar objects is mainly based on configural processing mechanisms.

Adaptation, Psychological↗

PubMed2005

Differences in onset latency of macaque inferotemporal neural responses to primate and non-primate faces.

Neurons in the visual system respond to different visual stimuli with different onset latencies. However, it has remained unknown which stimulus features, aside from stimulus contrast, determine the onset latencies of responses. To examine the possibility that response onset latencies carry information about complex object images, we recorded single-cell responses in the inferior temporal cortex of alert monkeys, while they viewed >1,000 object stimuli. Many cells responded to human and non-primate animal faces with comparable magnitudes but responded significantly more quickly to human faces than to non-primate animal faces. Differences in onset latency may be used to increase the coding capacity or enhance or suppress information about particular object groups by time-dependent modulation.

Animals↗

PubMed2004

Effects of neonatal C-fiber depletion on discrimination of principal and adjacent whisker stimulation within rat individual cortical barrels.

Controlled mechanical displacement was used to stimulate single whiskers in normal and C-fiber depleted rats to quantitatively examine the role of C-fibers in the response properties of barrel cortical cells. C-fiber depletion using neonatal capsaicin treatment increased the barrel single-unit response magnitude to deflection of both principal and adjacent whiskers while there was not any significant difference in the barrel cells' spontaneous activity. Capsaicin treatment increased the neural response duration of adjacent whisker stimulation but did not change that to the principal whisker deflection. There was no difference in response latencies of principal or adjacent whisker displacement between the normal and C-fiber-depleted groups. The efficiency of neural code for differentiation of principal and adjacent whiskers was measured by ROC analysis, which reflects the performance of an ideal observer in this discrimination using cells' firing rate. No significant difference was found in the performance of neurons in capsaicin-treated and control groups in distinguishing principal and adjacent whisker deflections from each other. These results suggest that neonatal C-fiber depletion causes an expansion of barrel cells receptive field but it does not affect the discrimination of individual whisker stimulation by the barrel cells.

Analysis of Variance↗

PubMed2004

Adaptation to apparent motion in crowding condition.

Visual adaptation has been successfully used for studying the neural activity of different cortical areas in response to visual stimuli when observers do not have explicit conscious access to those stimuli. We compared the orientation selective adaptation to apparent motion and its effect on the perception of stimuli with bistable apparent motion in crowded and non-crowded conditions. In the crowding paradigm conscious access to a visual stimulus is severely impaired when it is flanked by other similar stimuli in the peripheral visual field. As expected, adaptation to the target stimulus occurred in the non-crowded condition in all of the individual subjects (n=4; P<0.001). Although in the crowded condition subjects were not able to discriminate the target stimulus, adaptation to that stimulus was still preserved (P<0.001). There was no significant difference between the adaptations in the two conditions of the apparent motion (P>0.05). Imaging studies have shown that V5 cortex is the earliest visual area that specifically responds to apparent motion. Our results suggest that in certain conditions V5 may be activated while there is no explicit conscious access to the apparent motion.

Adaptation, Psychological↗

PubMed2004

Orientation-selective adaptation during motion-induced blindness.

When a global moving pattern is superimposed on high-contrast stationary or slowly moving stimuli, the latter occasionally disappear for periods of several seconds (motion-induced blindness, MIB). Here, an adaptation paradigm was used to determine if orientation-selective adaptation still occurs for the stimulus that is no longer visible. Two slowly drifting high-contrast Gabor patches were presented to observers. As soon as both patches disappeared, one was eliminated from the screen. After 2 s, two low-contrast Gabor patches were presented as tests at the same locations and observers were asked to report their orientations. The observers' performance was significantly higher when the orientation of the low-contrast test patch was orthogonal to the orientation of the high-contrast adapting patch (p < 0.0001) for the location where the patch was present during MIB, even though it was perceptually invisible. The observers' performance was not significantly different at the adjacent control location where the stimulus was absent during the MIB. Although no stimulus was visible at either location, orientation-selective adaptation was preserved only for the location at which the patch remained present. Since orientation information is processed in low-level visual areas such as the primary visual cortex (V1), we conclude that MIB originates in an area higher than V1.

Adaptation, Psychological↗

PubMed2004

Motion-induced overestimation of the number of items in a display.

Subjects were asked to report the number of items in a display as the items moved along a circular path around the fixation point. As the rotation speed increased, the apparent number of items also increased. This motion-induced overestimation (MIO) effect was investigated in three experiments. In the first experiment, the effect of rotation speed and set size was explored with an enumeration task. The overestimation error increased with an increase in speed or number of items in the display. In the second experiment, we used an adjustment paradigm to measure the speed threshold of MIO effect onset. Temporal rate of the display, which was defined as product of rotation speed and the number of rotating items, was the determining factor of MIO onset. In the third experiment, moving items were marked with different colours. Surprisingly, the number of perceived items was still overestimated even though the number of perceived colours was not.

Color Perception↗