Do some neurological conditions induce brain plasticity processes?

Neural correlates of extrinsic and intrinsic outcome processing during learning in individuals with TBI: a pilot investigation

Outcome processing, the ability to learn from feedback, is an important component of adaptive behavior and rehabilitation. Evidence from healthy adults implicates the striatum and dopamine in outcome processing. Animal research shows that damage to dopaminergic pathways in the brain can lead to a disruption of dopamine tone and transmission. Such evidence thus suggests that persons with TBI experience deficits in outcome processing. However, no research has directly investigated outcome processing and associated neural mechanisms in TBI. Here, we examine outcome processing in individuals with TBI during learning. Given that TBI negatively impacts striatal and dopaminergic systems, we hypothesize that individuals with TBI exhibit deficits in learning from outcomes. To test this hypothesis, individuals with moderate-to-severe TBI and healthy adults were presented with a declarative paired-associate word learning task. Outcomes indicating performance accuracy were presented immediately during task performance and in the form of either monetary or performance-based feedback. Two types of feedback provided the opportunity to test whether extrinsic and intrinsic motivational aspects of outcome presentation play a role during learning and outcome processing. Our results show that individuals with TBI exhibited impaired learning from feedback compared to healthy participants. Additionally, individuals with TBI exhibited increased activation in the striatum during outcome processing. The results of this study suggest that outcome processing and learning from immediate outcomes is impaired in individuals with TBI and might be related to inefficient use of neural resources during task performance as reflected by increased activation of the striatum.

FMRI contributions to addressing autobiographical memory impairment in temporal lobe pathology

Episodic autobiographical memory (AM) allows one, through the recollection of sensory-perceptual details, thoughts and feelings, to become aware of an event as belonging to one’s own past as well as being able to project into one’s future. Because AM provides a sense of self-continuity, contributes to the integrity of the self, and helps predicting future experiences, any deficit of AM may have debilitating consequences for everyday life functioning. Understanding AM failure and the underlying neural mechanisms has the potential to shed light on brain reorganization mechanisms and engagement of compensatory processes. Functional magnetic resonance imaging (fMRI) provides the most promising imaging method to tackle these issues. We reviewed evidence from the few studies that used fMRI to investigate the functionality of the residual tissue, the neural reorganization and compensatory mechanisms in patients with neurological conditions due to impaired medial temporal lobe. Overall, these studies highlight the importance of the left hippocampus, which when atrophied and not functional leads to AM deficits but its residual functionality may support relatively normal AM recollection. When damaged hippocampal tissue is not functional, other brain regions (e.g., the medial prefrontal cortex) may be involved to compensate impairment, but they appear generally ineffective to support detailed episodic recollection.

Functional MRI and neuropsychological evidence for language plasticity before and after surgery in one patient with left temporal lobe epilepsy

This study explores the language reorganization before and after surgery in a 55-year-old right-handed female patient presenting with left temporal refractory epilepsy. Two aspects of language were explored, phonological and semantic, by using neuropsychological assessments and fMRI protocols. To assess the possible reorganization of language, fMRI results for B.L. were compared with results obtained in a group of healthy control subjects (results not presented in detail). According to our results and compared with healthy subjects, B.L. shows reorganization of temporal regions only. The reorganization had various patterns according to the task. Before surgery, neuropsychological testing in B.L. revealed impairment in phonological abilities and fMRI suggested right temporal involvement (interhemisphere reorganization) during the phonological task; semantic abilities were unaltered and fMRI showed bilateral activation of temporal regions during the semantic task. After surgery, the phonological deficit disappeared and fMRI showed left perilesional location of temporal activation (intrahemispheric reorganization); semantic abilities remain preserved and temporal activation remained located bilaterally but predominantly to the right during the semantic task. Our results suggest that cerebral reorganization of language depends on the language operation tested. Moreover, the results underline the importance of differential assessment of language operations and show functional reorganization after beneficial surgery in an older patient.

Impaired event memory and recollection in a case of developmental amnesia

A current debate in the literature is whether all declarative memories and associated memory processes rely on the same neural substrate. Here, we show that H.C., a developmental amnesic person with selective bilateral hippocampal volume loss, has a mild deficit in personal episodic memory, and a more pronounced deficit in public event memory; semantic memory for personal and general knowledge was unimpaired. This was accompanied by a subtle difference in impairment between recollection and familiarity on lab-based tests of recognition memory. Strikingly, H.C.'s recognition did not benefit from a levels-of-processing manipulation. Thus, not all types of declarative memory and related processes can exist independently of the hippocampus even if it is damaged early in life.

The glutaminergic, GABAergic, dopaminergic but not cholinergic neurons are susceptible to anaesthesia-induced cell death in the rat developing brain

Neuronal cell death induced by anaesthetics in the developing brain was evident in previous pre-clinical studies. However, the neuronal cell types involved in anaesthesia-induced neuronal cell death remains elusive. The aim of this study was to investigate glutamatergic, GABAergic, cholinergic and dopaminergic neuronal cell apoptosis induced by anaesthetic exposure in specific brain regions in rats. Separate cohorts of 7-day-old Sprague Dawley (SD) rat pups were randomly assigned to two groups: Naive and anaesthetics alone (70% nitrous oxide and 0.75% isoflurane exposure for 6 h). The brains were sectioned and the slices that contained the basal forebrain, substantia nigra, cornu ammonis area 1 (CA1) subarea of hippocampus or cingulate cortex were selected and subsequently subjected to double-labelled fluorescent immunohistochemistry for choline acetyltransferase, dopamine, vesicular glutamate transporter 1 (vGLUT1) or glutamic acid decarboxylase 67 (GAD67) together with caspase 3, respectively. Compared to the naive control, anaesthetic exposure significantly increased the number of caspase-3 positive cells in the CA1 subarea of hippocampus, cingulate cortex, and substantia nigra, but not in the basal forebrain. 54% and 14% of apoptotic cells in the CA1 subarea of hippocampus were GABAergic and glutamatergic neurons respectively. In the cingulate cortex, 30% and 37% of apoptotic cells were GABAergic and glutamatergic neurons respectively. In the substantia nigra, 22% of apoptotic cells were dopaminergic neurons. Our data suggests, anaesthetic exposure significantly increases neuroapoptosis of glutamatergic, GABAergic and dopaminergic neurons in the developing brain but not that of the cholinergic neurons in the basal forebrain.

Deficits in past remembering extend to future imagining in a case of developmental amnesia

Patient and neuroimaging studies report that the ability to remember past personal experiences and the ability to envision future personal experiences are interconnected. Loss of episodic memory is typically accompanied by loss of future imagining, and engaging in either activity recruits common brain areas. The relationship between episodic memory and future imagining is also suggested by their co-emergence in ontogenetic development. However, it is unknown whether a failure of one ability to emerge in early development precludes the development of the other ability. To investigate this possibility, we tested H.C., a young woman with amnesia of developmental origin associated with bilateral hippocampal loss, and demographically matched controls on an adapted version of the Autobiographical Interview using Galton-Crovitz cueing. In response to cue words, participants described both past personal events and imagined future personal events that occurred, or could occur, in near and distant time periods. Results indicated a parallel pattern of impairment for both past and future event generation in H.C., such that her narratives of both types of events were similarly deficient. These results indicate that mental time travel can be compromised in hippocampal amnesia, whether acquired in early or later life, possibly as a result of a deficit in reassembling and binding together details of stored information from earlier episodes.

Implications of brain plasticity to brain-machine interfaces operation a potential paradox?

The adult brain has the remarkable ability to plastically reorganize itself in order to record memories (experiences), to add abilities, and to learn skills, significantly expanding the carnet of resources useful for facing and solving the unpredictability of any daily life activity, that is, artistic and cultural activities. Brain plasticity also plays a crucial role in reorganizing central nervous system's networks after any lesion, being it sudden and localized, or progressive and diffuse, in order to partly or totally restore lost and/or compromised functions. In severely affected neurological patients unable to move and to communicate with the external environment, technologies implementing brain-machine interfaces (BMIs) can be of valuable help and support. Subjects operating within a BMI frame must learn how to produce a meaningful signal for an external reader; how to increase the signal-to-noise ratio at a level which makes it suitable for rapid communication with the machine; and how to improve the speed and specificity (bit rate) of signal production as a new language for governing and controlling a machine. Since it is of absolute importance for the patient to be able to maintain such a skill for a prolonged lapse of time (i.e., until his/her lost abilities are restored by a therapy and/or a different technology), neurophysiological phenomena at the base of plastic changes are obviously of remarkable importance within any BMI and are the content of the present chapter.

Brain-machine interface via real-time fMRI: preliminary study on thought-controlled robotic arm

Real-time functional MRI (rtfMRI) has been used as a basis for brain-computer interface (BCI) due to its ability to characterize region-specific brain activity in real-time. As an extension of BCI, we present an rtfMRI-based brain-machine interface (BMI) whereby 2-dimensional movement of a robotic arm was controlled by the regulation (and concurrent detection) of regional cortical activations in the primary motor areas. To do so, the subjects were engaged in the right- and/or left-hand motor imagery tasks. The blood oxygenation level dependent (BOLD) signal originating from the corresponding hand motor areas was then translated into horizontal or vertical robotic arm movement. The movement was broadcasted visually back to the subject as a feedback. We demonstrated that real-time control of the robotic arm only through the subjects' thought processes was possible using the rtfMRI-based BMI trials.