Biology subjects

Kwok, S. C.

Publications and source records attributed to Kwok, S. C..

5 recordsLinked to original sources

bioRxiv2018

Individual susceptibility to TMS affirms the precuneual role in meta-memory upon recollection

BackgroundA recent virtual-lesion study using inhibitory repetitive transcranial magnetic stimulation (rTMS) confirmed the causal behavioral relevance of the precuneus in the evaluation of ones own memory performance (aka mnemonic metacognition).\n\nObjectiveThis studys goal is to elucidate how these TMS-induced neuromodulatory effects might relate to the neural correlates and be modulated by individual anatomical profiles in relation to meta-memory.\n\nMethodsIn a within-subjects design, we assessed the impact of 20-min rTMS over the precuneus, compared to the vertex, across three magnetic resonance imaging (MRI) neuro-profiles on 18 healthy subjects during a memory versus a perceptual task.\n\nResultsTask-based functional MRI revealed that BOLD signal magnitude in the precuneus is associated with variation in individual meta-memory efficiency, and such correlation diminished significantly following TMS targeted at the precuneus. Moreover, individuals with higher resting-state functional connectivity (rs-fcMRI) between the precuneus and the hippocampus, or smaller grey matter volume in the stimulated precuneal region exhibit considerably higher vulnerability to the TMS effect. These effects were not observed in the perceptual domain.\n\nConclusionWe provide compelling evidence in outlining a possible circuit encompassing the precuneus and its mnemonic midbrain neighbor the hippocampus at the service of realizing our meta-awareness during memory recollection of episodic details.\n\nHighlightsO_LITMS on precuneus reduces meta-memory ability during memory retrieval.\nC_LIO_LITMS disrupts the correlation between BOLD activity and meta-memory ability.\nC_LIO_LITMS effect is modulated by rs-fcMRI between precuneus and hippocampus.\nC_LIO_LIIndividuals with greater precuneal grey matter volume more immune to TMS effect.\nC_LI

neuroscience↗

bioRxiv2018

Mnemonic introspection in macaques is dependent on dorsolateral prefrontal but not orbitofrontal cortex

The human prefrontal cortex (PFC) has been associated more with meta-perceptual as opposed to meta-memory decisions from correlational neuroimaging investigations. Recently, metacognitive abilities have also been shown to be causally dependent upon anterior and dorsal PFC in non-human primate lesion studies. Two studies, utilizing post-decision wagering paradigms and reversible inactivation, challenged this meta-perceptual versus meta-memory notion and showed that dorsal and anterior prefrontal areas are associated with metamemory for experienced objects and awareness of ignorance respectively. Causal investigations are important but scarce; nothing is known, for example, about the causal contributions of prefrontal sub-regions to spatial metamemory. Here, we investigated the effects of dorsal versus ventral PFC lesions on two-alternative forced choice spatial discrimination tasks in male macaque monkeys. Importantly, we were rigorous in approach and applied three independent but complementary indices used to quantify individual animals metacognitive ability ("type II sensitivity") namely meta-d', d' measures, and Phi coefficient ({Phi}). Our results were consistent across indices: while neither lesions to superior dorsolateral PFC (sdlPFC) nor orbitofrontal cortex (OFC) impaired spatial recognition performance, only monkeys with sdlPFC lesions were impaired in meta-accuracy. Together with the observation that the same OFC lesioned monkeys were impaired in updating rule-value in a Wisconsin Card Sorting Test analog, we therefore document a functional double-dissociation between these two PFC regions. Out study presents important causal evidence that other dimensions, namely domain-specific processing (e.g., spatial versus non-spatial metamemory), also need considerations in understanding the functional specialization in the neural underpinnings of introspection. Significance StatementThis study demonstrates macaque monkeys meta-cognitive capability of introspecting its own memory success is causally dependent on intact superior dorsolateral prefrontal cortices (PFC) but not the orbitofrontal cortices. Combining neurosurgical techniques on monkeys and state-of-the-art measures of metacognition, we affirm a critical role of the PFC in supporting spatial meta-recognition memory and delineate functional specificity within PFC for distinct elements of metacognition.

neuroscience↗

bioRxiv2018

Time-dependent mnemonic vulnerability induced by new-learning

Reactivation renders consolidated memory labile again, and the ensuing temporary reconsolidation process is highly susceptible to mnemonic modification. Here, we show that memories in such an unstable state could be reprogrammed by sheer behavioral means, bypassing the need for pharmacological intervention. In two experiments using a \"face-location associationc\" paradigm in which participants experienced a \"Learning - New-learning - Final-test\" programme, we demonstrate that reactivated memory traces were robustly hampered when the new learning was strategically administered within a critical 20-minute time window. Using fMRI, we further advance our theoretical understanding that this lability can be mechanistically explained by the differential activation in the hippocampal-amygdala memory system implicated by the new-learning whereas the mnemonic intrusion caused by newly learned memories is efficaciously reconciled by the left inferior frontal gyrus. Our findings provide important implications for educational and clinical practices in devising effective strategies for memory integration.

neuroscience↗

bioRxiv2018

Causal evidence for mnemonic metacognition in human precuneus

Metacognition is the capacity to introspectively monitor and control ones own cognitive processes. Previous anatomical and functional neuroimaging findings implicated the important role of precuneus in metacognition processing, especially during mnemonic tasks. However, the issue of whether this medial parietal cortex is a domain-specific region that supports mnemonic metacognition remains controversial. Here, we focally disrupted this parietal area with repetitive transcranial magnetic stimulation in healthy participants of both sexes, seeking to ascertain its functional necessity for metacognition for memory versus perceptual decisions. Perturbing the precuneal activity impaired the metacognitive efficiency selectively in the memory judgment of temporal-order, but not in perceptual discrimination. Moreover, the correlation in individuals metacognitive efficiency between the domains disappeared when the precuneus was perturbed. Together with the previous finding that lesion to the anterior prefrontal cortex impairs perceptual but not mnemonic metacognition, we double dissociated the macro-anatomical underpinnings for the two kinds of metacognitive capacity in an interconnected network of brain regions.\n\nSIGNIFICANCE STATEMENTTheories on the neural basis of metacognition have thus far largely centered on the role of prefrontal cortex. Here we refined the theoretical framework through characterizing a unique precuneal involvement in mnemonic metacognition with a noninvasive but inferentially powerful method: transcranial magnetic stimulation. By quantifying meta-cognitive efficiency across two distinct domains (memory vs. perception) that are matched for stimulus characteristics, we reveal an instrumental - and highly selective - role of the precuneus in mnemonic metacognition. These causal evidence corroborate ample clinical reports that parietal lobe lesions often produce inaccurate self-reports of confidence in memory recollection and establish that the precuneus as a nexus for the introspective ability to evaluate the success of memory judgment in humans.

neuroscience↗

bioRxiv2018

Locally distributed abstraction of temporal distance in human parietal cortex

An enduring puzzle in the neuroscience of memory is how the brain parsimoniously situates past events by their order in relation to time. By combining functional MRI, and representational similarity analysis, we reveal a multivoxel representation of time intervals separating pairs of episodic event-moments in the posterior medial memory system, especially when the events were experienced within a similar temporal context. We further show such multivoxel representations to be vulnerable to disruption through targeted repetitive transcranial magnetic stimulation and that perturbation to the mnemonic abstraction alters the neural--behavior relationship across the wider parietal memory network. Our findings establish a mnemonic \"pattern-based\" code of temporal distances in the human brain, a fundamental neural mechanism for supporting the temporal structure of past events, assigning the precuneus as a locus of flexibly effecting the manipulation of physical time during episodic memory retrieval.

neuroscience↗