Biomedical subjects

Gagan S Wig

Publications and source records attributed to Gagan S Wig.

7 recordsLinked to original sources

PubMed2005

Reductions in neural activity underlie behavioral components of repetition priming.

Repetition priming is a nonconscious form of memory that is accompanied by reductions in neural activity when an experience is repeated. To date, however, there is no direct evidence that these neural reductions underlie the behavioral advantage afforded to repeated material. Here we demonstrate a causal linkage between neural and behavioral priming in humans. fMRI (functional magnetic resonance imaging) was used in combination with transcranial magnetic stimulation (TMS) to target and disrupt activity in the left frontal cortex during repeated classification of objects. Left-frontal TMS disrupted both the neural and behavioral markers of priming. Neural priming in early sensory regions was unaffected by left-frontal TMS--a finding that provides evidence for separable conceptual and perceptual components of priming.

Adult↗

PubMed2005

Conditioned effects of kindling three different sites in the hippocampal complex of the rat.

Rats received kindling stimulations to the perirhinal cortex (PRh), ventral hippocampus (VH), or dorsal hippocampus (DH) in 1 environment and an equivalent number of sham stimulations in a 2nd environment. The PRh-kindled rats displayed rapid kindling and a swift emergence of conditioned interictal defensiveness. In contrast, the VH- and DH-kindled rats displayed much slower kindling and slow or no conditioning, respectively. No effects of conditioning on the convulsions, comparable with those associated with amygdala kindling, were observed. These results establish the generality of some of the previously reported kindling-related conditioned effects, confirm the site specificity of some of these effects, and suggest that the convulsions, rather than the stimulations, function as the unconditioned stimuli for the conditioning of interictal behavior.

Animals↗

PubMed2004

Neural correlates of humor detection and appreciation.

Humor is a uniquely human quality whose neural substrates remain enigmatic. The present report combined dynamic, real-life content and event-related functional magnetic resonance imaging (fMRI) to dissociate humor detection ("getting the joke") from humor appreciation (the affective experience of mirth). During scanning, subjects viewed full-length episodes of the television sitcoms Seinfeld or The Simpsons. Brain activity time-locked to humor detection moments revealed increases in left inferior frontal and posterior temporal cortices, whereas brain activity time-locked to moments of humor appreciation revealed increases in bilateral regions of insular cortex and the amygdala. These findings provide evidence that humor depends critically upon extant neural systems important for resolving incongruities (humor detection) and for the expression of affect (humor appreciation).

Adult↗

PubMed2004

Searching for patterns in random sequences.

In a probability-guessing paradigm, participants predict which of two events will occur on each trial. Participants generally frequency match even though frequency matching is nonoptimal with random sequences. The optimal strategy is to guess the most frequent event, maximizing. We hypothesize that frequency matching results from a search for patterns, even in random sequences. Using both callisotomy patients and patients with frontal brain damage, Wolford, Miller, and Gazzaniaga (2000) found frequency matching in the left hemisphere but maximizing in the right hemisphere. In this paper, we show that a secondary task that competes for left hemisphere resources moves the participants toward maximizing but that a right-hemisphere task preserves frequency matching. We also show that a misunderstanding of randomness contributes to frequency matching.

Analysis of Variance↗

PubMed2003

Stimulation site determines the conditioned effects of kindling in rats: anterior neocortex versus amygdala.

Rats received 53 stimulations to either the left basolateral amygdala (BA) or left anterior neocortex (AN) in one environment (CS+) and 53 sham stimulations (the stimulation lead was attached but no current was delivered) in another environment (CS-), quasirandomly over 54 days. Confirming a previous report [Barnes, S.J., Pinel, J.P., Francis, L.H. & Wig, G.S. (2001) Behav. Neurosci., 115, 1065-1072], as BA kindling progressed, the CS+ began to elicit more defensive behaviours (i.e. less activity, more freezing and avoidance of the CS+) than the CS-, and at the end of the experiment, convulsions elicited in the CS+ were more severe than those elicited in the CS-. Like BA kindling, AN kindling led to less activity in the CS+; but unlike BA kindling, AN kindling led to more wet-dog-shakes and less, rather than more, severe convulsions in the CS+. During AN kindling, the mean number of wet-dog-shakes in the CS+ was negatively correlated with the mean convulsion class, suggesting that wet-dog-shakes contribute to the inherent variability of AN kindling. These findings confirm that inherent conditioned effects influence kindled convulsions and interictal behaviour and establish for the first time that the pattern of these conditioned effects is a function of the kindling site.

Amygdala↗

PubMed2002

Conditioning of a flavor aversion in rats by amygdala kindling.

Rats received 30 stimulations and 30 sham stimulations (the lead was attached to the subjects but no current was delivered) to the left basolateral amygdala in a quasirandom sequence. Stimulations were preceded by the presentation of 1 flavored solution conditional stimulus (CS+); sham stimulations were preceded by the presentation of another flavored solution, CS-. As kindled motor seizures developed, the rats began to consume significantly less of the CS+ than the CS-. Moreover, at the end of the experiment, the rats consumed significantly less of the CS+ than the CS- during a 20-min conditioned flavor preference test in which both solutions were available simultaneously. These findings confirm and extend the recent report that interictal changes in defensive behavior can be conditioned by amygdalar kindling.

Amygdala↗

PubMedDate not supplied

Separable routes to human memory formation: dissociating task and material contributions in the prefrontal cortex.

The present study used fMRI to investigate functional dissociations across frontal regions during incidental memory formation. Subjects were imaged while encoding materials with differential access to phonological codes (nonfamous faces and nameable famous faces) under task conditions that encouraged elaborate (deep) or superficial (shallow) encoding strategies. Results revealed a functional dissociation between dorsal posterior regions of the prefrontal cortex (BA 6/44) that were sensitive to material type (famous vs. nonfamous), irrespective of the encoding task, and ventral anterior regions of the prefrontal cortex (BA 45/47) that were uniquely sensitive to task demands (deep vs. shallow), regardless of material type. Further, subjects realized a memorial advantage to the extent that they recruited these dissociable frontal regions. These results demonstrate a posterior/anterior dichotomy in the frontal cortex that underlies separable code-based routes to human memory formation.

Adolescent↗