Transcranial magnetic stimulation over MT/MST fails to impair judgments of implied motion.

The medial temporal and medial superior temporal cortex (MT/MST) is involved in the processing of visual motion, and fMRI experiments indicate that there is greater activation when subjects view static images that imply motion than when they view images that do not imply motion at all. We applied transcranial magnetic stimulation (TMS) to MT/MST in order to assess the functional necessity of this region for the processing of implied motion represented in static images. Area MT/MST was localized by the use of a TMS-induced misperception of visual motion, and its location was verified through the monitored completion of a motion discrimination task. We controlled for possible impairments in general visual processing by having subjects perform an object categorization task with and without TMS. Although MT/MST stimulation impaired performance in a motion discrimination task (and vertex stimulation did not), there was no difference in performance between the two forms of stimulation in the implied motion discrimination task. MT/MST stimulation did, however, improve subjects' performance in the object categorization task. These results indicate that, within 150 msec of stimulus presentation, MT/MST is not directly involved in the visual processing of static images in which motion is implied. The results do, however, confirm previous findings that disruption of MT/MST may improve efficiency in more ventral visual processing streams.

Normal attention orienting but abnormal stimulus alerting and conflict effect in combined subtype of ADHD.

Recent pharmacological studies in animals and neuroimaging studies in normal humans suggest that the spatial and nonspatial cues in tasks measuring reflexive attention may be modulated by different neurotransmitter systems. The efficiency with which attention is oriented to explicit spatial cues may be altered by manipulating levels of brain acetylcholine, whereas reactions to nonspatial cues may be influenced by altering brain noradrenaline levels but not acetylcholine levels. In humans, however, previous attention studies have implicated dopamine when either explicit or implicit cueing is used. Some of the differences between animal and human work may be due to inadequate testing of nonspatial cues. To remedy this, we tested adult humans with ADHD that were primarily inattentive (ADHD/I) or combined inattentive/hyperactive (ADHD/C) and controls with the Attention Network Task that assesses both reflexive and voluntary attention and explicitly tests nonspatial cueing. Our results showed that spatial orienting in both subtypes was no different than controls. However, ADHD/C but not ADHD/I subjects had significantly slowed response times to nonspatial cues and cues with spatial conflict. Stimulant medication in a subset of ADHD/C subjects reduced these deficits to control levels. Based on these results, we conclude that ADHD/C subjects orient the focus of their attention normally but are impaired in their reactions both to abrupt visual cues and those that contain conflicting spatial cues.

Salivary cotinine levels in human tobacco smokers predict the attentional validity effect size during smoking abstinence.

RATIONALE: The link between attention and brain cholinergic neurotransmission is widely accepted. Human chronic tobacco smokers maintain high levels of nicotine in plasma and body tissues and show enhanced attentional orienting and other attentional tasks. OBJECTIVE: We wished to test whether abstinence from smoking caused levels of the nicotine metabolite cotinine to decline and attentional enhancement to be reduced in a correlated manner. METHODS: The levels of salivary cotinine and behavioral performance on a cued target detection task were measured in chronic, adult tobacco smokers over a 5-day abstinence period. Control groups assessed over the same time period include non-smokers, smokers that did not abstain from tobacco, and smokers that abstained for 4 days and smoked on the last day. RESULTS: In all groups with tobacco exposure, the levels of cotinine declined steadily with time after abstinence, reaching near zero levels at day 5. During this period, reaction times declined as well for all groups, due in part to task practice effects. In contrast, the validity effect, which indexes attentional allocation, increased with abstinence and was inversely related to cotinine levels in groups exposed to tobacco. CONCLUSIONS: We conclude that 1) nicotine abstinence increases the attentional validity effect, and 2) this increase is indexed by salivary cotinine, and 3) that control levels of attentional performance are achieved after 3-4 days of tobacco abstinence.