Multisensory Integration and the Body Schema: Close to Hand and Within Reach

Multisensory Integration and the Body Schema: Close to Hand and Within Reach
http://www.icn.ucl.ac.uk/WebSpace/users/attentiongrp/pubs/Jon%20Driver/Author/Original%20Research%20Papers/2003/Current%20Biology%2013%20R531%20R539.pdf

For instance, a multisensory neuron with a tactile receptive
field (RF) on one hand will typically respond to visual
stimulation near that hand, thereby increasing its rate
of firing as the visual stimulus approaches the tactile
RF, and declining as it is moved away.

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Incongruent visual
distractors have been shown to delay tactile judgments
and to produce more erroneous responses, leading to a
crossmodal congruency effect, which is defined as the
performance difference between incongruent versus
congruent trials. Importantly, this crossmodal congruency
effect is more pronounced for a visual distractor
near the tactually stimulated hand than for one near the
other hand, or elsewhere


In addition to such effects of discrete visual precueing
events on tactile judgments (or vice versa), some
other recent studies [33–35] have shown that continuous
rather than discrete vision of the hand or arm can
also modulate tactile performance for the corresponding
body part, even when no additional information
about the position of the tactile stimulus or its identity
is provided by vision

the activation of a subset of such multisensory neurons
by a spatial stimulus in one sensory modality might
lead to an enhanced response from the same neurons
to a second stimulus, which is presented at the same
(or similar) external location, but in a different sensory
modality and to which the activated neurons also
respond

 crossmodal congruency effect

 (B) The
magnitude of this effect (shown numerically)
is reduced when the stuffed rubber
gloves are placed in an anatomically
implausible posture.

 When the hand was occluded below a
screen, neurons responded more to the
vision of a taxidermied monkey arm (dark
brown) aligned over the real arm, if the
dummy arm matched the real arm (C), but
less if a taxidermied contralateral arm was
placed at the same location (D).

However, the rubber
hands produced no such modulatory effect when
placed in an anatomically implausible posture (Figure
2B) that was totally inconsistent with the real hands’
actual posture

Thus, while purely visual information
(i.e. sight of the rubber hands) can dominate slightly discrepant
proprioception (Figure 2A), proprioception may
reduce the impact of vision when the visual information
about hand position is inconsistent with proprioception
(Figure 2B). In agreement with this notion, in the total
absence of vision of any hands (real or dummy), proprioceptive
information about current hand posture (e.g.
crossed or uncrossed hands, or hands placed near
versus far from one another) has been shown to modulate
crossmodal interference effects [29]

These results indicate that visual information about
body position seems to strongly influence ‘body-partcentred’
multisensory spatial representations [54].
These representations, at least in area 5, may even be
detailed enough to incorporate visual discrimination
between a left or right hand [55]. But if the arm of a
trained monkey is actively or passively moved underneath
an occluding screen, so that no arm — neither
real nor dummy — is visible, some remapping can still
be shown to occur in the anterior bank of the intraparietal
sulcus (IPS) [56] and/or premotor cortex [54], with
the visual RF tending to shift along with the unseen
arm as its position changes. Thus, if sensory modalities
are in conflict (e.g. when viewing dummy hands),
plausible visual information about arm or hand location
can dominate proprioception, perhaps due to the
greater spatial acuity of vision. It is, however, also clear
that proprioceptive/kinaesthetic information can play
some role, as shown in the absence of visual information
about limb position. The same point applies to the
crossmodal congruency effects reported in human
performance, which can show visual dominance when
a dummy hand is seen in a possible location for the
real hand, but can still be modulated by proprioceptive
information about actual hand location under conditions
of occlusion or darkness

Figure 3. Apparent expansion of the
representation of peripersonal space
around the hand following tool-use, or
when viewing the hand only indirectly via a
distant mirror-reflection.

Thalamic deactivation at sleep onset precedes that of the cerebral cortex in humans

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2840430/

Why Daydreamers Are More Creative

 http://www.psychologytoday.com/blog/beautiful-minds/201102/why-daydreamers-are-more-creative

When most of us fall asleep, the brain network that involves attention to the outside world (the working memory network consisting primarily of the lateral frontal and parietal cortices) deactivates and our default brain network (medial prefrontal and posterior cingulate cortices) takes over. The discovery of the default brain network is important, as it involves various aspects of our self, such as our self-representations, dreams, imagination, current concerns, autobiographical memory and perspective-taking ability. Those with higher default network activity during rest have a tendency to daydream more frequently, which makes sense if one thinks of the default network as involving our inner stream of consciousness.
. In most people, the working memory network and the default network "anticorrelate" with each other,

Creative folks and those with schizophrenia tend to have an overactive default network. Prior research has suggested that the thing that seems to differentiate creative but functional individuals from those in a mental institution is that the functional folks appear to have the ability to engage both brain networks, and they can use their working memory network to control their attention. Those who lose grip on reality and become paranoid and delusional have let the floodgates down, so to speak, letting too much of their default network control their attention 

  The creativity test they used has been linked in prior studies to Openness to Experience and frequency of visual hypnagogic experiences (e.g. lucid dreaming, hallucinations), which in turn have been associated with vividness of mental imagery.


The researchers found that the more creative the participant, the more activity in their default-mode network was altered. Particularly, creative individuals had difficulty suppressing the precuneus area of their default network while engaging in the more effortful working memory task. The precuneus is the area of the default network that typically displays the highest levels of activation during rest (when a person is not focusing on an external task). The precuneus has been linked to self-related mental representations and episodic memory retrieval. 

 

The role of the right temporoparietal junction in intersensory conflict: detection or resolution?

The right temporoparietal junction (rTPJ) is a polysensory cortical area that plays a key role in perception and awareness. Neuroimaging evidence shows activation of rTPJ in intersensory and sensorimotor conflict situations, but it remains unclear whether this activity reflects detection or resolution of such conflicts. To address this question, we manipulated the relationship between touch and vision using the so-called mirror-box illusion. Participants’ hands lay on either side of a mirror, which occluded their left hand and reflected their right hand, but created the illusion that they were looking directly at their left hand. The experimenter simultaneously touched either the middle (D3) or the ring finger (D4) of each hand. Participants judged, which finger was touched on their occluded left hand. The visual stimulus corresponding to the touch on the right hand was therefore either congruent (same finger as touch) or incongruent (different finger from touch) with the task-relevant touch on the left hand. Single-pulse transcranial magnetic stimulation (TMS) was delivered to the rTPJ immediately after touch. Accuracy in localizing the left touch was worse for D4 than for D3, particularly when visual stimulation was incongruent. However, following TMS, accuracy improved selectively for D4 in incongruent trials, suggesting that the effects of the conflicting visual information were reduced. These findings suggest a role of rTPJ in detecting, rather than resolving, intersensory conflict.

Remote Excitation of Neuronal Circuits Using Low-Intensity, Low-Frequency Ultrasound

Article

Notes:

low-intensity, low-frequency ultrasound (LILFU) 

 By transmitting US waveforms through hippocampal slice cultures and ex vivo mouse brains, we determined LILFU is capable of remotely and noninvasively exciting neurons and network activity. Our results illustrate that LILFU can stimulate electrical activity in neurons by activating voltage-gated sodium channels, as well as voltage-gated calcium channels. The LILFU-induced changes in neuronal activity were sufficient to trigger SNARE-mediated exocytosis and synaptic transmission in hippocampal circuits. Because LILFU can stimulate electrical activity and calcium signaling in neurons as well as central synaptic transmission we conclude US provides a powerful tool for remotely modulating brain circuit activity.

*Transcranial ultrasonography of the basilar artery has been shown to trigger auditory sensations in human subjects Other studies have reported similar observations in animals during delivery of transcranial US and at least one underlying mechanism is thought to involve the direct stimulation of auditory nerve fibers by US

 *The frequency of US we chose for the construction of LILFU waveforms (0.44–0.67 MHz) represents a range where optimal gains have been previously reported between transcranial US transmission and brain absorption. Based on modeling data of transmission and attenuation coefficients, as well as experimental data examining the transmission of US through ex vivo human skulls, the optimal gain for the transcranial US transmission and brain absorption is between 0.60 and 0.70 MHz [25], [26]. Based on our observations and the findings of others, it is likely that LILFU fields can be transmitted through skulls into the intact brain for gross neurostimulation purposes similar to methods using rTMS. In order to achieve targeted neurostimulation however, it will be necessary to focus LILFU fields.

*It is possible to focus US fields using a variety of approaches. Pulsed US (<1 MHz) can be focused through human skulls to points within 1 mm of intended loci using phased US transducer arrays [6], [8], [59]. Based on observations reported in studies designed to investigate US field focusing through human skulls [6], [8], [59], US may be able to confer a spatial resolution similar to those achieved by currently implemented neuromodulation strategies such as vagal nerve stimulation and DBS, which have been shown to possess high therapeutic value [1], [60]. 

Ethics of neural enhancement using noninvasive brain stimulation

Article

Notes:

Another area where the potential of cognitive enhancement
holds great promise is language learning.
Anodal tDCS over Broca’s area has been shown to
improve the ability of subjects to learn new object
names and may also enhance the ability to learn
novel grammar.14,15.In other investigations, TMS
and tDCS of language-related regions of the left
hemisphere has been shown to induce faster object
naming,16,17 and anodal tDCS applied to the left prefrontal
cortex has been shown to transiently improve
verbal fluency.18

•  14. Flo¨el A, Ro¨sser N, Michka O, Knecht S, Breitenstein C.

Noninvasive brain stimulation improves language learning.
J Cogn Neurosci 2008;20:1415–1422.

• 15. de Vries MH, Barth AC, Maiworm S, Knecht S, Zwisterlood

P, Flo¨el A. Electrical stimulation of Broca’s area enhances
implicit learning of an artificial grammar. J Cogn
Neurosci Epub 2009 Nov 19.

• 17. Sparing R, Dafotakis M, Meister IG, Thirugnanasambandam

N, Fink GR. Enhancing language performance with
non-invasive brain stimulation: a transcranial direct current

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 After inhibitory noninvasive brain
stimulation of the right DLPFC, subjects were more
likely to accept low offers, even though they still perceived
them as being unfair. It seems as though subjects
were more motivated to act in their self-interest
than to abstain from a reward for the sake of fairness.
TMS and tDCS of the DLPFC have also been shown
to manipulate behavior on a variety of other rewardseeking
tasks.38

• 37. Knoch D, Pascual-Leone A, Meyer K, Treyer V, Fehr E.

Diminishing reciprocal fairness by disrupting the right
prefrontal cortex. Science 2006;314:829–832.

• 38. Fecteau S, Knoch D, Fregni F, Sultani N, Boggio P, Pascual-

Leone A. Diminishing risk-taking behavior by modulating
activity in the prefrontal cortex: a direct current stimulation
study. J Neurosci 2007;27:12500–12505.